Download Kinetic chain weight training

Kinetic chain weight training,
strength assessment,
and functional performance testing
With reference to
sports and rehabilitation
Jesper Augustsson
Department of Orthopaedics
Institute of Surgical Sciences and
Rehabilitation Medicine
Institute of Clinical Neuroscience
The Sahlgrenska Academy at Göteborg University
Göteborg, Sweden
2003
ISBN 91-628-5852-1
“No Pain, No Gain”
BODY BUILDING EXPRESSION
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Contents
Abstract 6
List of papers 7
Abbreviations and definitions 8
Introduction 10
Weight training 10
Strength assessment 16
Closed and open kinetic chain 21
Functional performance testing 26
Rehabilitation after ACL reconstruction 28
Summary of problem areas presented in the introduction
32
Aims of the investigation 33
Subjects 34
Ethics 36
Methods 37
Statistical methods 42
Summary of the papers 44
Discussion 52
Kinetic chain weight training and
strength assessment (Studies I, II and III) 52
Functional performance testing (Studies IV and V) 55
Limitations 57
Conclusions 58
Clinical relevance 60
The future 61
Abstract in Swedish 62
Acknowledgements 64
References 66
Papers I-V 75−
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Kinetic chain weight training, strength assessment,
and functional performance testing
With reference to
sports and rehabilitation
Jesper Augustsson
Abstract. The overall purpose of the studies was to obtain knowledge about physical performance
in healthy individuals and patients after anterior cruciate ligament (ACL) reconstruction. Data are
presented that concerns closed and open kinetic chain exercise, adaptive response to weight training,
the methodology of muscle strength assessment, and the development of a functional testing
protocol performed under conditions of fatigue.
Study I: The purpose of this study was to compare the effect of closed versus open kinetic chain
weight training of the thigh muscles. Healthy subjects performed closed (n=12) and open (n=12)
kinetic chain weight training twice a week for six weeks. Both groups increased in a barbell squat
test, although the closed kinetic chain group improved more than the open kinetic chain group. The
closed kinetic chain group improved their jumping ability, however, there was no difference across
groups. Large improvements in isotonic strength in both groups did not transfer to an isokinetic
knee-extension test.
Study II: The purpose of this study was to investigate the ability of closed and open kinetic chain
strength tests to assess functional performance in 16 healthy male subjects. Moderately strong
correlations were found between a barbell squat test, an isokinetic knee-extension test, and a vertical
jump test. It is suggested that the effect of training or rehabilitation interventions should not be
based exclusively on tests of muscular strength. Instead, various forms of dynamometry including
functional performance tests could be recommended.
Study III: The purpose of this study was to investigate the effect of “pre-exhaustion” exercise
(knee-extension) on lower-extremity muscle activation during a leg press exercise. Seventeen
healthy male subjects performed one set of a leg press exercise with and without pre-exhaustion.
The electromyography activation of the vastus lateralis and the rectus femoris muscles was less
when pre-exhausted. Our findings do not support the popular belief that performing pre-exhaustion
exercise more effectively enhances muscle activity compared with regular weight training.
Study IV: A pre-exhaustion exercise protocol was combined with single-leg hop testing to improve
the possibilities to evaluate the effects of training or rehabilitation interventions. High test-retest
reliability was noted for 11 healthy male subjects performing non-fatigued and fatigued hop testing.
Additionally, we investigated how fatigue influences lower-extremity joint kinematics and kinetics
during single-leg hops. Absorbed power during landing was two to three times greater for the knee
than for the hip and five to ten times greater for the knee than for the ankle across test conditions.
Study V: A new hop test, performed under conditions of fatigue, was investigated to determine
functional deficits after ACL reconstruction. Although no patients (n=19) displayed abnormal hop
symmetry when non-fatigued, two thirds showed abnormal hop symmetry for the fatigued hop
condition. It is concluded that a fatigue exercise protocol combined with the single-leg hop test
improved testing sensitivity when evaluating lower-extremity function after ACL reconstruction.
Conclusions: Although strength measurements are important to monitor the effect of training and
rehabilitation interventions, they cannot fully assess functional performance. Functional deficits
after ACL reconstruction may become more apparent during conditions of fatigue. For a more
comprehensive evaluation of lower-extremity function after ACL reconstruction, it is therefore
suggested that functional testing should be performed under both non-fatigued and fatigued test
conditions.
Key words: open kinetic chain, closed kinetic chain, weight training, strength assessment,
functional tests, anterior cruciate ligament, reconstruction, fatigue
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List of papers
The present thesis is based on the following papers, which will be referred to in
the text by their Roman numerals.
I. Weight training of the thigh muscles using closed vs. open kinetic chain
exercises: a comparison of performance enhancement. Augustsson J, Esko
A, Thomeé R, Svantesson U. J Orthop Sports Phys Ther 1998: 27: 3−8.
II. Ability of closed and open kinetic chain tests of muscular strength to assess
functional performance. Augustsson J, Thomeé R. Scand J Med Sci Sports
2000: 10: 164−168.
III. Effect of pre-exhaustion exercise on lower-extremity muscle activation
during a leg press exercise. Augustsson J, Thomeé R, Hörnstedt P,
Lindblom J, Karlsson J, Grimby G. J Strength Cond Res 2003: 17:
411−416.
IV. Development of a single-leg hop test performed under fatigued conditions
using pre-exhaustion exercise: reliability and biomechanical analysis.
Augustsson J, Thomeé R, Lindén C, Folkesson M, Tranberg R, Karlsson J.
Accepted Scand J Med Sci Sports.
V. Ability of a new hop test to determine functional deficits after anterior
cruciate ligament reconstruction. Augustsson J, Thomeé R, Karlsson J.
Knee Surg Sports Traumatol Arthrosc 2004: 12: 350−356.
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Abbreviations and definitions
In the present thesis, the following abbreviations and definitions were used.
ACL. Anterior cruciate ligament.
Closed kinetic chain. Weight-bearing movement or exercise that involves
muscles working across multiple joints (a barbell squat exercise, for example).
Concentric muscle action. When the muscle shortens while producing force.
Dynamic muscle action. Involving either an increase or decrease in joint
angles.
Eccentric muscle action. When a muscle lengthens while producing force.
EMG. Electromyography.
ICC. Intraclass correlation coefficient.
Isokinetic muscle action. Refers to a muscle action performed at a constant
angular joint velocity. Unlike other types of weight training, there is no specified
resistance to meet; rather, the velocity of movement is controlled. The resistance
offered by an isokinetic dynamometer cannot be accelerated; any force applied
against the machine results in an equal reaction force.
Isometric muscle action. When a muscle is activated and develops force but no
movement at a joint occurs, an isometric muscle action takes place.
Isotonic muscle action. Refers to an exercise performed at a variable speed
with fixed resistance. The term isotonic (iso + tonic = same tension) implies
constant tension. The execution of free weight and weight machine exercises is
usually regarded as isotonic; however, dynamic action of a muscle in exercise
and sports hardly ever involves constant force development. As a result, the term
‘isotonic’, implying uniform force throughout a dynamic muscle action, has
therefore been considered inappropriate (Knuttgen and Komi 1992).
Kinematics. The study of movements which describes the motion of a joint.
Kinetics. Static and dynamic analysis of the forces and moments acting on a joint.
MVIA. Maximal voluntary isometric activation.
Nm. Newton meter.
Open kinetic chain. Non-weight-bearing movement or exercise that involves
muscles working across only single joints (a weight machine knee-extension
exercise, for example).
Power. Power is the rate of performing work; the product of force and velocity
(SI unit: Watt). Power during a repetition is defined as the weight lifted
multiplied by the vertical distance the weight is lifted divided by the time it
takes to complete the repetition.
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Power absorption. The ability of the muscle to perform work (negative power)
during the eccentric phase of a movement. Absorbed power of the quadriceps
muscle, for example, occurs when walking down stairs.
Power generation. The ability of the muscle to perform work (positive power)
during the concentric phase of a movement. Generated power of the quadriceps
muscle, for example, occurs when walking up stairs.
Repetition maximum (RM). This is the maximum number of repetitions per set
that can be performed until failure at a given resistance using a proper exercise
technique. So, a set at a certain RM implies that the set is performed to
momentary voluntary fatigue. 1 RM is the heaviest resistance that can be lifted
for one complete repetition of an exercise. 8 RM, for example, is a lighter
resistance that allows completion of eight, but not nine, repetitions using a
proper exercise technique.
Repetition. A repetition is one (complete) movement of an exercise. It normally
consists of two phases: the concentric muscle action, in which the muscle
shortens, and the eccentric muscle action, in which the muscle lengthens.
SD. Standard deviation.
SEM. Standard error of the mean.
Set. This is a group of repetitions normally performed continuously without
stopping. While a set can be made up of any number of repetitions, sets during
weight training typically range from one to 20 repetitions.
Strength. Strength is the maximal amount of force a muscle or muscle group
can generate in a specified movement pattern at a specified velocity (including
an isometric muscle action) of movement.
Stretch-shortening cycle. A common pattern of muscle activation in everyday
activity and athletic competition is to combine eccentric and concentric
activations. Such sequencing of muscle action is termed a stretch-shortening
cycle.
Weight training. The terms resistance, weight, and strength training have all
been used to describe a type of exercise that requires the body’s musculature to
move (or attempt to move) against an opposing force, usually presented by some
type of equipment. The terms resistance and strength training encompasses a wide
range of training modalities, including plyometrics (drop jumps, for example) and
hill running. Weight training, on the other hand, is typically used to refer only to
training using free weights, such as barbells and dumb-bells, or weight machines.
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Introduction
Weight training: brief history
The human ability to generate muscle force has fascinated mankind throughout
most of recorded history. A 140 kg block of red sandstone found in Olympia had
a 6th-century inscription stating that the weight lifter Bybon, using only one
hand, had lifted it over his head. The Greek athlete Milos of Crotona has been
credited with the first use of progressive resistance exercise. It is reported that he
lifted a bull-calf every day until it was fully grown, and that he was eventually
able to carry the bull around the stadium at Olympia (Fry et al. 2002b). Records
indicated that Galen (A.D. 129–199), considered the most outstanding physician
since Hippocrates in ancient times, classified exercises into those that exercised
the muscles without violent movement (e.g. digging, weightlifting), quick
exercises that promote activity (e.g. ball play, rolling on the ground), and violent
exercises (Gardiner 1930). The 19th and early 20th century was the era of the
strongmen in Europe and North America (Fry et al. 2002b). Canadian strongman
Louis Cyr (1863-1912) is possibly the strongest man who ever lived. He might
have performed the greatest strength feat in history when he once lifted a
platform carrying eighteen men, a total of more than 2000 kg, on his back. In
1886, Louis Cyr set a record by lifting up a weight of 251 kg using just the
middle finger of his right hand. The strongest woman in the world (relative to
body mass) is arguably power lifter Carrie Boudreau of the United States, who is
the current world record holder in the 56-kg weight class with a 222.5 kg dead
lift (Vanderburgh and Dooman 2000). In the 1940s, research into the field of
strength training increased, with investigators experimenting with more precise
training prescriptions. Pioneers of strength research include Thomas L. De
Lorme and Peter V. Karpovich, who wrote the first science-based articles and
books on the subject of strength training (De Lorme and Watkins 1948; Murray
and Karpovich 1956). This work is thought to have revolutionised the field of
training athletes and was also adopted as textbooks in many physical education
classes (Todd and Todd 2003). In 1946, De Lorme developed an exercise
strategy based on the notion that muscles should be tested when exerting
“maximum effort”. To make his idea applicable to clinical settings his exercise
programmes were based on a single maximal contraction of muscles through the
full range of motion. He called this maximum effort the “one repetition
maximum” or 1 RM (De Lorme 1946).
Traditionally, weight training was limited to sports like power lifting, body
building, and Olympic weightlifting. More recently, however, the pursuit of
sporting achievement has resulted in the increased use of weight training by
other athletes to enhance sporting performance. In fact, sports that do not utilise
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resistance training have become the exception rather than the rule (Kraemer et
al. 2002).
Benefits of weight training
Weight training impacts several body systems, including the muscular, endocrine,
skeletal, metabolic, immune, neural, and respiratory systems (Deschenes and
Kraemer 2002). Trainable fitness characteristics when performing weight
training include muscular strength, power, hypertrophy, and local muscular
endurance. Other variables such as speed, balance, co-ordination, jumping
ability, flexibility, and other measures of motor performance have also been
positively enhanced (Colliander and Tesch 1990; Delecluse et al. 1995;
Rutherford and Jones 1986; Stone et al. 1981; Thrash and Kelley 1987).
Resistance training has become increasingly popular in the general
population, and it is regarded as the most effective method available for
maintaining and increasing lean body mass and improving muscular strength
and endurance in healthy populations (Hass et al. 2001). The benefits for elderly
individuals of regular participation in resistance-training programmes include
improvements in bone density, muscle mass, arterial compliance and energy
metabolism, which may offset age-, inactivity- and disease/disability-associated
declines in functional capacity (Mazzeo and Tanaka 2001). Moreover, resistance
training has proven effective for the prevention and rehabilitation of orthopaedic
injuries (Feigenbaum and Pollock 1999). Further, participation in exercise
programmes incorporating resistance training has been shown to reduce the risk
of several chronic diseases (coronary heart disease, obesity, diabetes mellitus,
and osteoporosis, for example) (Hass et al. 2001).
Intensity (load)
The intensity of the exercise (i.e. the amount of resistance used) is arguably the
most important variable in weight training (Kraemer et al. 1998). The intensity
of an exercise can be estimated as a percentage of the 1 RM or any RM for the
exercise. The minimal intensity that can be used to perform a set to momentary
voluntary fatigue to result in increased strength is still unclear. Traditionally,
loads of less than 60% of 1 RM have been considered insufficient and resulting
in no strength gains (McDonagh and Davies 1984). At least 80% of 1 RM is
thought to be needed to produce any further strength increases in experienced
lifters (Häkkinen et al. 1985). However, Takarada and Ischii (2002a)
investigated the effects of weight training with low intensity (50% of 1RM) and
a short interset rest period (30 seconds). The results showed considerable effects
of the exercise regimen that, in spite of its low intensity, had a considerable
effect in inducing muscular hypertrophy and a concomitant increase in strength.
Rhea et al. (2003) carried out a meta-analysis of 140 weight training studies to
identify the magnitude of strength gains along the continuum of training
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intensities. It was concluded that training with a mean intensity of 60% of 1 RM
elicits maximal gains in untrained individuals, whereas 80% is most effective in
those who are trained. In power lifting, however, where the principal training
goal is to optimise maximal strength, training is rarely carried out using loads
below 90% of 1 RM (Fleck and Kraemer 1997).
It has recently been reported that low-intensity (30-50% of 1 RM)
resistance training, combined with moderate vascular occlusion, produced gains
in strength that were greater than those produced by low-intensity resistance
training alone and were comparable to those achieved after conventional highintensity resistance training (Shinohara et al. 1998; Takarada et al. 2000a;
Takarada et al. 2002b).
Taken together, the optimal training intensity to achieve maximal gains in
strength and muscle volume, assuming that an optimal intensity actually exists,
remains unclear.
Training volume
Training volume is a summation of the total number of repetitions and sets
performed during a training session multiplied by the resistance used. A change
in training volume can be accomplished by changing the number of exercises
performed per session, the number of repetitions performed per set, or the
number of sets per exercise. The relationship between training volume and
muscular hypertrophy is not clear. However, some authors claim that a
relationship exists, as body builders, who often use large training volumes,
develop large muscles (Fleck and Kraemer 1997). Studies using two or more
sets per exercise have all produced significant increases in muscular strength in
both trained and untrained individuals (Dudley and Djamil 1985; Staron et al.
1994; Hortobagyi et al. 1996; Housh et al. 1992).
One aspect of training volume that has recently received considerable
attention is the comparison of single- and multiple-set resistance training
programmes (i.e. the number of sets completed of each exercise) (Carpinelli and
Otto 1998; Feigenbaum and Pollock 1999; Hass et al. 2000; Kraemer et al.
2002; McBride et al. 2003; Paulsen et al. 2003, Rhea et al. 2003). The
proponents of single-set programmes conclude that they elicit similar gains in
strength and hypertrophy as multiple sets (Carpinelli and Otto 1998;
Feigenbaum and Pollock 1999; Hass et al. 2000). Further, single-set
programmes are regarded as less time consuming and more cost efficient, which
may translate into improved programme compliance, e.g. during rehabilitation
of orthopaedic injuries (Feigenbaum and Pollock 1999). Supporters of multiple
sets, on the other hand, claim that trained subjects are clearly dependent on
multiple sets to ensure strength progress and hypertrophy (Kraemer et al. 2002;
McBride et al. 2003; Paulsen et al. 2003, Rhea et al. 2003). At present, there is
no clear consensus on this topic, and there appears to be a need for studies in
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which this topic is further explored in different ways (e.g. untrained versus
trained subjects, short-term versus long-term adaptations, periodised versus nonperiodised training, and small muscle groups versus large muscle groups).
Rest between sets
This acute training variable can be manipulated to provide great variety in the
metabolic characteristics of the training session. Training intensity is affected by
the rest intervals, so these variables are related. When high power activities or
high load exercises are performed, long rest intervals (e.g. 3-5 minutes) are often
used to allow adequate recovery before subsequent sets are performed (Fry et al.
2002a). When maximal hypertrophy is the main training goal, exercises are often
performed to muscular exhaustion, and rest intervals between sets are very short
(e.g. 30 to 60 seconds). Methods such as pre-exhaustion exercise, in which two
different exercises are performed without any rest between them, are also often
used by weight trainers when hypertrophy is desired (Augustsson et al. 2003).
However, the effects of fatigue on muscle function and the implications of
this in terms of strength and muscle hypertrophy acquisition are not well
documented and existing data relating to whether fatigue may stimulate strength
and muscle volume development are contradictory. Rooney et al. (1994)
reported that fatiguing, continuous repetitions resulted in greater strength gains
compared with when rest was taken between repetitions. Similarly, Schott et al.
(1995) demonstrated greater strength gains and muscle hypertrophy following
strength training using long, fatiguing activations compared with short,
intermittent activations. Conversely, Pincivero et al. (1997b) examined the
influence of rest intervals on strength gains subsequent to high-intensity training
and reported that a longer rest period between sets resulted in a greater
improvement in muscle strength. The results obtained by Pincivero et al.
(1997b) are supported by the observation that the development of fatigue is not
desirable in power lifting, where the principal training goal is to optimise
maximal strength (Fleck and Kraemer 1997).
Taken together, it is not clear whether the duration of the rest intervals
between sets is of importance if the objective is to bring about maximal muscle
hypertrophy and strength gains.
Frequency
The optimal training frequency (the number of workouts per week) may depend
on several factors such as training volume, intensity, exercise selection, training
status, recovery ability, and the number of muscle groups trained per workout
session (Kraemer et al. 2002).
The frequency of training appears to differ by training status. In untrained
individuals, a consistent dose-response was noted, as the number of days each
muscle group was trained increased up to three days a week. For trained
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individuals, two days a week elicited the greatest strength increases (Rhea et al.
2003). Unfortunately, the effect of training each muscle group on only one day a
week in trained individuals was not investigated. However, training each muscle
group only once a week (or even more infrequently) is common practice among
experienced weight trainers (Augustsson 2002), and this approach requires
further scientific study.
Increasing training frequency may enable greater specialisation (e.g.
greater exercise selection and volume per muscle group in accordance with more
specific goals). Performing upper-body exercises during one workout and lowerbody exercises during a separate workout (upper/lower-body split) or training
specific muscle groups (split routines) during a workout are common at
advanced levels of training in addition to total-body workouts. For those
individuals desiring a change in training structure (e.g. upper/lower-body split,
split workout), an overall frequency of three to four days a week has been
recommended, so that each muscle group is only trained one or two days a week
(Fleck and Kraemer 1997). However, the optimal frequency necessary for
progression during advanced split-routine training remains unknown.
Free weights versus machines
The Swedish physician and scientist Gustaf Zander is sometimes credited with
being the first inventor and manufacturer of weight training machines, in the
1860s (Söderberg 1999) (Figure 1). Therapists, coaches and athletes design and
implement resistance-training programmes that involve both free weights and
weight machines. These programmes are often designed in an attempt to
improve strength, power, and ultimately athletic and functional performance.
The pros and cons of training with free weights versus weight machines are
widely discussed, both among athletes and coaches, among physical therapists
and in sports science. Differences of opinions exist as to which method would
result in optimal performance gains.
The proponents of free weights (barbells and dumb-bells) feel that they are
versatile, require balance and co-ordination, much like actual sporting events,
allow for small incremental adjustments in resistance, and allow for multiplanar
movements compared with weight machines. The believed disadvantages of free
weights are that some movements (bench press, squats and so on) require
spotters or special racks; and they may also be psychologically intimidating to
some novice trainees. Moreover, several body movements are difficult to
exercise with free weights. One example would be torso transverse rotation,
which is important for combative sports such as wrestling and judo, for example
(Haff 2000).
The general advantages of resistance exercise machines are thought to be
that they do not usually intimidate novice users; they can be designed to provide
resistance in any direction; do not generally require a spotter for safety; they are
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less likely than free weights to cause injury to a user who is inept or careless;
and they may be organised in a circuit to provide a fast and convenient way to
exercise all major muscle groups. The believed disadvantages of resistance
exercise machines are that they generally provide for the sequential training of
isolated muscle groups rather than training major muscle groups in unison and
that they do not usually lend themselves to ballistic or “explosive” exercises
such as weighted jumps (Haff 2000).
Finally, although there are theoretical advantages and disadvantages to free
weights and weight machines, there is no strong scientific evidence to support
the superiority of one modality over the other. For example, perhaps more
balance and coordination are required to perform free weight exercises
compared with machine exercises, but there is no evidence that this skill has any
significant transfer to other activities, such as running, jumping or throwing. In
accordance, we compared six weeks of free weight with weight machine training
for the lower-extremities and found that there were no differences across groups
in a vertical jump test (Augustsson et al. 1998).
Figure 1. Picture of the Swedish physician and scientist Gustav Zander in 1865, here
seen performing “biceps curls” in his self-invented weight training machine (Photo:
Swedish Museum of Science and Technology, Stockholm, Sweden).
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Strength assessment
Ancient cultures utilised tests of muscular strength for both entertainment and
utilitarian purposes. For example, strength tests were being used for military
purposes as early as during the Chou dynasty in China (1122-255 BC) (Fry et al.
2002b). More recently, various dynamometers (e.g. for assessment of grip
strength) were developed and adopted by neurologists in the late 19th century to
measure muscle strength, in keeping with the general trend at that time of
adopting instrumentation to distinguish and aid observation and diagnosis
(Lanska 2000).
Purposes of assessment
Tests of muscular strength and power are commonly performed to assess
functional performance, in both the sporting and the rehabilitation fields.
Monitoring strength performance may be useful for many groups of individuals,
ranging from the high-velocity power testing of the elite athlete to the ability of
an elderly individual to rise from a chair. According to Abernethy et al. (1995),
strength and power are assessed for four main purposes: 1) to quantify the
relative significance of strength and power to various athletic events and tasks;
2) to identify the specific deficiencies in muscular function to improve
individual deficiencies (i.e. strength diagnosis); 3) to identify individuals who
may be suited to particular athletic pursuits (i.e. talent identification) and 4) to
monitor the effects of training or rehabilitation interventions.
Dynamometry
Currently, methods of strength assessment fall into three main
categories−isometric, isokinetic and isotonic testing (Abernethy et al. 1995).
Isometric strength is the maximal voluntary muscle activation that can be
developed against an immovable object, without a change in joint angle. Often
both the maximum force and the rate of force development are recorded.
Isokinetic assessments involve the measurement of torque and power through a
range of motion in which the limb is moving at a constant angular velocity.
Maximal isotonic strength (i.e. the 1 RM) is often used as a measure of strength
for athletic profiling and is regarded by some as the “gold standard” of dynamic
strength testing (Franklin 2000).
Each method is considered to have drawbacks, the main argument against
isometric assessment being that isometric tests bear little resemblance to the
dynamic nature of most sporting activities (Wilson and Murphy 1996). The
perceived disadvantage of isokinetic assessment is the absence of acceleration
and stretch-shortening cycle, and that single joint, isolated assessments, such as
seated knee-extensions, are often used, even though they bear little resemblance
to functional performance (Fry et al. 1991; Sleivert et al. 1995; Wilson et al.
1993). Those opposed to isotonic assessment tend to emphasise poor reliability
16
and objectivity due to inter-subject, inter-trial and inter-laboratory variations
(Abernethy et al. 1995).
Reliability of different forms of dynamometry
Ideally, all sports medicine procedures should be reliable. A threat to the
reliability of strength tests is the proximity of the assessment to previous training
sessions. The time it takes to recover isotonic, isometric and isokinetic strength
after an intensive bout of weight training or strength testing is far from well
investigated (Abernethy et al. 1995; Michaut et al. 2003). Moreover, the effect
of endurance training prior to strength assessment has not been sufficiently
studied. The recommended time that the physical activity of healthy subjects or
patients should be limited prior to strength assessment is therefore unclear.
Isometric dynamometry
Isometric assessment techniques generally present high test-retest reliability
(Blazevich et al. 2002; Chiu and Sing 2002; Meldrum et al. 2003; Wilson et al.
1993). However, reliability coefficients may vary depending on several factors.
For instance, Agre et al. (1987) reported poorer reliability coefficients for lowerlimb (0.20 to 0.96) than for upper-limb (0.85 to 0.99) isometric strength testing.
Moreover, work by Christ et al. (1994) indicates that reliability varies between
muscle groups. The ICCs for the maximal voluntary isometric activation of
dorsiflexors and forearm extensors were 0.55 and 0.64, respectively, while the
coefficients were 0.94 and 0.91 for the plantar and forearm flexors.
Isometric tests usually involve participants producing a maximal force
against an immovable resistance, which is in series with a strain gauge, cable
tensiometer, force platform or similar device whose transducer measures the
applied force (Wilson and Murphy 1996). However, we have developed a new
method for measuring maximal isometric muscle strength, using a conventional
weight training machine (M. Bruno et al. unpublished work) (Figure 2). This
isometric test showed high test-retest reliability for both women (r=0.94) and
men (r=0.99).
Isokinetic dynamometry
Generally, the test-retest reliability of isokinetic tests is high. Research groups
have reported high reliability coefficients (>0.90) for several isokinetic devices,
including the Kin-Com, the Cybex and the Biodex system (Wilk 1990).
Reliability, however, decreases as the contractile speed increases (Oesternig
1986). Although the reliability coefficients for eccentric muscle actions appear
to be slightly less than those for concentric muscle actions, they remain high
(r>0.90) (Seger et al. 1988).
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Figure 2. The principle for determining maximal isometric strength, using a
conventional weight training machine. As the subject performed a muscle action
that dislodged a particular test weight, a cord attached to a free-weight plate fell out
of the weight stack and the trial was considered successful. The weight lifted was
incremented by 2.5-10 kg until the subject failed to dislodge the test weight within
five seconds (M. Bruno et al. unpublished work).
Isotonic dynamometry
The observed test-retest reliability of 1 RM measurements amongst experienced
male and female weight trainers is high (r=0.91 to 0.98) (Hortobagyi et al. 1989;
Hennessey and Watson 1994; Hoeger et al. 1990; M. Bruno et al. unpublished
work). More dynamic tests, such as the weighted squat jump, appear to be
equally reliable; for example, Stone et al. (2003) reported high test-retest
reliability for a weighted squat-jump test (ICC=0.88).
Correlations between strength measures and functional performance
The number of published studies correlating tests of strength with functional
performance is limited in the literature. This is somewhat surprising, as this kind
of information allows us to determine the relationship a particular test of
strength has with running, jumping or throwing, for example. In cases where
there are meaningful correlations it is, for example, possible to determine
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whether differences in strength discriminate between levels of performance and
whether training and rehabilitation interventions affect strength measures.
It is currently not clear when an individual is regarded as fully rehabilitated
and fit for full sports participation (Murphy et al. 2003; Parkkari et al. 2001). It
is also not known whether strength tests can be used to predict future
performance, and thereby, reduce the risk of re-injury, for example, when an
individual returns to sport following rehabilitation. More detailed studies are
therefore needed about the risk of re-injury, when individuals with reduced leg
strength return to sports participation after anterior cruciate ligament (ACL)
reconstruction, for example. In knee rehabilitation literature, the vast majority of
studies show persisting side-to-side differences in thigh muscle strength after
ACL reconstruction (Anderson et al. 2002; Arangio et al. 1997; Carter and
Edinger 1999; Ernst et al. 2000; Hiemstra et al. 2000; Keays et al. 2003; Lewek
et al. 2002; Mattacola et al. 2002; Pfeifer and Banzer 1999; Risberg et al. 1999;
Urbach et al. 2001; Wojtys and Huston 2000). In ACL rehabilitation, protocols
are often used in which a recommended minimum leg muscle strength must be
achieved corresponding to 85 or 90%, for example, compared with the nonoperated limb, before no restrictions are needed be taken in sport and work
activities (Østerås et al. 1998). However, the relationship between tests of
muscular function and functional performance is still not clear. Recent studies,
however, indicate a relatively low relationship between tests of muscle function
and dynamic performance, both in healthy subjects (Murphy and Wilson 1997;
Wilson et al. 1997) and in subjects with ACL-reconstruction (Pfeifer and Banzer
1999). Pincivero et al. (1997a) studied the relationship between concentric
isokinetic quadriceps and hamstring strength values with the single-leg hop for
distance, a functional activity. It was concluded that only low to moderate
relationships existed between the single-leg hop and the knee strength tests.
Although the degree of difference in strength performance between the two
lower-extremities has not been shown to have a definite relationship with a
propensity towards injury during athletic activities (Williams et al. 2001), a
difference of 10% or more can be considered to reflect a real difference in the
capacity of performance (Sapega 1990). Taken together, our research group
regard a side-to-side difference of more than 10% between the involved and
non-involved leg following ACL reconstruction as unsatisfactory for strength
test scores, and believe that it may predispose an individual to overuse and/or
acute injuries when returning to sports or strenuous work.
Sensitivity of different tests to the effects of training or rehabilitation
One important issue is whether isometric, isotonic and isokinetic tests are
sensitive to the effects of various training and rehabilitation regimens; and
whether these tests are similarly sensitive to the effects of training and
rehabilitation.
19
According to several studies (Augustsson et al. 1998; Sleivert et al. 1995;
Wilson et al. 1993), isokinetic tests are not sensitive to isotonic weight training
strength improvements. The rationale for performing isokinetic tests in clinical
practice is therefore somewhat weak, as weight training during rehabilitation is
typically performed using free weights and weight machines in an isotonic mode
alone. Murphy and Wilson (1997) examined the ability of isokinetic and isotonic
tests of muscular function to track weight training-induced changes in
performance. The results showed that weight training (barbell squats)
significantly enhanced sprint time. However, apart from the squat, no measure
of muscular function significantly changed because of training. Murphy and
Wilson (1997) therefore suggested that tests of muscular function cannot be
used to monitor training-induced changes in performance, and that the
effectiveness of training should be based on changes in performance rather than
changes in test scores of muscle function. However, the restoring of muscle size
and strength is a cornerstone of rehabilitation; and tests of muscular function
must therefore be regarded as important (Augustsson and Thomeé 2000).
20
Closed and open kinetic chain
Definitions
The terms “closed kinetic chain” and “open kinetic chain” have gained
considerable attention in the field of rehabilitation in recent years. A closed
kinetic chain exercise involves muscles working across multiple joints, whereas
an open kinetic chain exercise uses muscles working across only single joints.
Moreover, in an open kinetic chain, the distal segment terminates free in space,
whereas, in a closed kinetic chain, the distal segment is fixed (Brunnstrom
1983). A barbell squat is a free weight, closed kinetic chain exercise, involving
muscles working across multiple joints. Athletes, using resistance training, often
include the barbell squat exercise into their programmes to improve lowerextremity strength. Several studies have used a barbell squat test to determine
the effect of various training and rehabilitation interventions (Hickson et al.
1994; Wilson et al. 1997). Isokinetic or isotonic testing and training such as
weight machine knee-extension/flexion, using muscles working across only
single joints in an open kinetic chain, are also commonly used to evaluate and
improve lower-extremity strength (Fry et al. 1991; Thomeé et al. 1995) (Figure
3).
Figure 3. A barbell squat is a free weight, closed kinetic chain exercise, involving
muscles working across multiple joints (left picture). The weight machine knee extension
exercise involves muscles working across a single joint in an open kinetic chain (right
picture). Photos by Roland Thomeé and Marko Ervasti.
21
Biomechanical studies
In sports medicine literature, there is currently a preference for closed kinetic
chain exercises, based on the assumption that these exercises more closely
approximate functional activities, such as running or jumping (Lutz et al. 1993;
Wilk et al. 1996). Additionally, it is believed that the strain that some open
kinetic chain exercises place on the maturing graft may adversely affect the
long-term stability of the reconstructed knee (Bynum et al. 1995; Yack et al.
1993). Biomechanical, electromyographic, and strain gauge studies have been
used to compare closed and open kinetic chain exercises. In response, some
authors have recommended the exclusive use of closed kinetic chain exercise
and the exclusion of traditional open kinetic chain exercise (Bynum et al. 1995;
Kvist and Gillquist 2001). It has been concluded, however, that both types of
exercises can be performed in ways that do not place excessive strain on the
ACL (Fitzgerald 1997). When comparing knee joint biomechanics during closed
and open kinetic chain weight training at a 12 RM load, Escamilla et al. (1998)
reported that peak ACL tension forces in open kinetic chain exercise were 0.2
times body weight, and non-existent in closed kinetic chain exercise (Figure 4).
Fleming et al. (2001), on the other hand, noted that weight-bearing (closed
kinetic chain) exercise produced higher ACL strain values than non-weightbearing (open kinetic chain) exercise.
Force (N)
5000
Barbell squat
4000
3000
Leg press
2000
Knee extension
1000
0
ACL tension
Patellofemoral
compression
Figure 4. Escamilla et al. (1998) quantified knee forces in closed kinetic chain exercise
(squat and leg press) and open kinetic chain exercise (knee-extension). Ten healthy
male subjects performed three repetitions of each exercise at their 12 RM. Tension in
the anterior cruciate ligament was present only in open kinetic chain exercise, and
occurred near full extension (0.2 times body weight). Patellofemoral compressive force
was greatest in closed kinetic chain exercise near full flexion and in the mid-range of the
knee extending phase in open kinetic chain exercise (four to five times body weight).
22
Factors such as joint compressive forces (e.g. axial loading) and joint
geometry probably play integral roles in knee joint stability during closed
kinetic chain exercise (Isear et al. 1997), whereas the significant co-activation of
the antagonists during maximal knee flexion/extension, indicating an inhibitory
mechanism which may prevent overloading of the joint and contribute to joint
stabilisation (Kellis and Baltzopoulos 1998), would explain the low ACL
tension forces during open kinetic chain exercise.
Taken together, only minor differences in ACL strain values have been
reported when comparing closed and open kinetic chain exercises (Beynnon et
al. 1997a). Further, despite numerous studies (Escamilla et al. 1998; Fleming et
al. 2001; Kvist and Gillquist 2001; Wilk et al. 1996; Yack et al. 1993) of the
biomechanics of the knee during closed and open kinetic chain exercises, the
limits of strain that are safe for an uninjured or healing graft are currently still
unknown (Beynnon et al. 2002).
Testing
Strength assessment for rehabilitation or sports purposes can be performed using
either closed or open kinetic chain movement. However, few studies have
compared the ability of closed and open kinetic chain tests of muscular strength
to assess functional performance. In a study by Blackburn and Morrissey (1998),
open kinetic chain knee extensor strength demonstrated very low correlation
with vertical jump (r=0.01) and standing long-jump (r=0.07) performance,
whereas Petschnig et al. (1998), who studied the relationship between an
isokinetic quadriceps strength test and four different functional performance
tests in healthy subjects and patients with surgery to the ACL, reported
moderately strong correlation coefficients (between r=0.45 and r=55). In a
review (Abernethy et al. 1995) of articles in which correlations between
muscular strength tests and functional performance were investigated,
relationships typically ranged between r=0.50 and r=0.93. It is concluded that,
although tests of strength are often used to monitor training-induced changes in
performance or the effectiveness of rehabilitation, the relationship between tests
of muscular function and functional performance is not clear.
In certain circumstances, both closed and open kinetic chain testing could
be regarded as having low validity. As a diagnostic test, a closed kinetic chain
movement, involving several groups of muscles working across multiple joints,
is unable to determine the extent to which a particular muscle is activated
(Salem et al. 2003). Conversely, the open kinetic chain test, because of its more
“non-functional” nature, is able to isolate a specific muscle and thereby detect
dysfunction. The purpose of assessment should therefore determine which mode
of dynamometry that should used. To identify specific deficiencies or problem
areas, open kinetic chain strength testing would be preferable, whereas a closed
kinetic chain test may be better suited to assess functional performance.
23
Training
Quadriceps muscle hypotrophy and weakness frequently follows ACL injury
and reconstruction (Anderson et al. 2002; Arangio et al. 1997; Carter and
Edinger 1999; Ernst et al. 2000; Hiemstra et al. 2000; Keays et al. 2003; Lewek
et al. 2002; Mattacola et al. 2002; Pfeifer and Banzer 1999; Risberg et al. 1999;
Urbach et al. 2001; Wojtys and Huston 2000). Because this muscle is an
important extensor and stabiliser of the knee joint, the restoration of quadriceps
muscle mass and strength is regarded as paramount for successful ACL
rehabilitation (Bodor 2001). Despite the importance of this muscle, however,
there is currently no consensus regarding the optimal therapeutic prescription for
restoring its function after ACL surgical repair. Therapeutic exercise selection
has changed from the classical model (e.g. limited weight bearing,
immobilisation, open kinetic chain exercises) (Johnson et al. 1992; Fu et al.
1992) to the current “aggressive” model emphasising early weight bearing,
functional progression, and closed kinetic chain exercises (Beynnon 2002;
Bynum et al. 1995).
Although effective ways of exercise training during rehabilitation
following ACL reconstruction are still lacking, surprisingly few studies have
attempted to compare the effect of different training regimes. However,
Mikkelsen et al. (2001) conducted a prospective, randomised study that
compared closed kinetic chain and combined closed and open kinetic chain
rehabilitation initiated six weeks after ACL reconstruction. A six month followup revealed that the addition of open kinetic chain exercises produced a
significant improvement in quadriceps strength, an earlier return to sport at the
preinjury level, and did not affect measurements of anteroposterior knee laxity.
The authors therefore recommended a combination of closed and open kinetic
chain exercises to be used after ACL reconstruction, rather than performing only
closed kinetic chain exercises.
The barbell squat exercise is a traditional closed kinetic chain exercise that
has become an integral part of most lower-extremity strengthening and
postoperative ACL rehabilitation programmes (Augustsson et al. 1998; Salem et
al. 2003). The multiple-joint characteristics of a closed kinetic chain exercise
such as the squat, however, may allow patients to use intra-limb substitution
patterns that shift the effort from a targeted muscle group (e.g. knee extensors)
to another muscle group (e.g. hip extensors) (Isear et al. 1997). Moreover, when
these exercises are performed bilaterally, patients may shift the effort from the
targeted limb (i.e. involved limb) to the contralateral limb. These substitution
patterns may ultimately limit the effectiveness of the intervention exercise—
preventing the correction of weakness in the involved limb (Salem et al. 2003).
Additionally, strength training studies using closed kinetic chain exercises, but
testing isolated quadriceps function alone, have found no statistically significant
increases in quadriceps strength during open kinetic chain strength measures,
24
even though increases in strength were identified by using closed kinetic chain
strength measures (Augustsson et al. 1998).
Taken together, these findings suggest that the exclusive use of closed
kinetic chain exercises, for the purpose of reversing isolated quadriceps
hypotrophy and dysfunction after ACL reconstruction, could be less effective
compared with using both closed and open kinetic chain exercises.
25
Functional performance testing
During the rehabilitation of injuries to the lower-extremities, the assessment of
the patient’s capacity is usually based on different scores, e.g. the Tegner
activity score (Tegner and Lysholm 1985), on static measures (passive anterior
tibiofemoral joint laxity, presence of pivot shift) (Sernert 2002), on the results of
isokinetic strength measurements and often mainly on the subjective impression
of the patient and the therapist (Pfeifer and Banzer 1999; Rudolph et al. 2000).
Functional dynamic tests, however, are being used increasingly in the clinical
setting and are recommended in sports medicine literature (Greenberger and
Paterno 1995). These tests quantitatively measure (e.g. time, height, distance)
the abilities of injured extremities and also provide information about the
loading capacity in sport-specific situations, for example (Pfeifer and Banzer
1999).
Types of functional tests
Several types of functional tests (e.g. drop jump, figure-of-eight hop) have been
investigated in order to try to identify the functional limitations of patients after
ACL injury or reconstruction (Barber et al. 1990; Gauffin et al.1990; Itoh et al.
1998; Noyes et al. 1991; Tegner et al. 1986; Woodhouse et al. 1992). Among
these, the hopping-type tests have been most commonly reported (Rudolph et al.
2000). Noyes et al. (1991) developed a series of hop tests to allow clinicians to
compare the performance of the injured limb and the uninjured limb in persons
with ACL deficiency. They reported that a side-to-side hop symmetry of less
than 85% indicated diminished knee function that was related to quadriceps
muscle weakness and patient self-assessment of difficulty with pivoting
movements. Hop symmetry is now used as a standard measure of knee function
in ACL-deficient and reconstructed individuals (Ageberg 2002). Hop tests have
also been used to predict potential to succeed in non-surgical management and
to advance patients to sport-specific rehabilitation activities following ACL
reconstruction (Fitzgerald et al. 2000; Fitzgerald et al. 2001).
Sensitivity of functional tests
Researchers use single-leg hop tests to study knee function in ACL-deficient
persons particularly because hopping is more challenging than walking or
jogging and is thought by some to more closely represent the demands of highlevel sports (Fitzgerald et al. 2000; Fitzgerald et al. 2001; Hefti et al. 1993;
Noyes et al. 1991). However, the reported sensitivity of these tests in detecting
functional limitations in ACL-deficient knees was relatively low, ranging from
38% to 58% (Noyes et al. 1991; Tegner et al. 1986). In order to accurately
evaluate functional disability after ACL injury or reconstruction, it would be
desirable to have a test with a higher sensitivity rate. Moreover, injuries often
tend to occur at the end of a sporting event, when a participant is fatigued
26
(Dugan and Frontera 2000, Feagin et al. 1987, Murphy et al. 2003; Östenberg
and Roos 2000). However, it has been our observation that current functional
tests, such as the single-leg hop, are typically performed under non-fatigued test
conditions in both the clinical and the scientific setting. The ability of these tests
to assess whether a patient has regained lower-extremity function after ACL
reconstruction, for example, could therefore be regarded as limited. To improve
the sensitivity of tests of lower-extremity function to evaluate the effect of
rehabilitation interventions, the testing of dynamic function under fatigued
conditions has therefore been suggested (Augustsson and Thomeé 2000). It
could be hypothesised that performing single-leg hops under conditions of
fatigue may be more sensitive in detecting functional impairment after ACL
reconstruction, compared with traditional, non-fatigued hop testing.
Taken together, the sensitivity of dynamic tests in detecting functional
limitations after ACL reconstruction should be a question for further study.
27
Rehabilitation after ACL reconstruction
Background
ACL injuries continue to be a source of major concern for athletes, researchers,
and clinicians, due to their high incidence and long time for recovery (Fithian et
al. 2002). It appears as if an ACL injury increases the risk for early development
of osteoarthritis in the knee, regardless of whether ACL reconstruction is
performed or not (Roos and Karlsson 1998).
Injury to the ACL may result in mechanical and functional instability.
Athletes often find it difficult to return to full function after injury to the ACL,
and surgery is frequently indicated (Fu et al. 2000). The long-term prognosis for
sports participation after an ACL injury is uncertain, both after non-surgical
treatment and after the reconstruction of the ruptured ligament (Beynnon et al.
2002; Roos and Karlsson 1998). However, the possibilities of a return to elite
sports are illustrated by the fact that several players in the Swedish national
soccer team, for example, have undergone ACL reconstruction. The literature on
follow-up between five and 10 years after ACL reconstruction indicates that the
incidence of revision ACL reconstruction ranges from 3 to 10% (Noyes and
Barber-Westin 2001).
Postoperative rehabilitation
The surgical management of and rehabilitation programmes for ACL injuries
have evolved during the last decade. In the past, the procedure was performed in
an open fashion, frequently followed by several weeks of immobilisation. A
return to sports a year or more postoperatively was considered the norm. Today,
the procedure is routinely performed arthroscopially whereas rehabilitation has
become more “aggressive”, including immediate motion and weight-bearing and
an early return to sports (Shelbourne and Nitz 1992; Shelbourne at al. 1995). It
is now customary to allow return to full sports activities six months after the
procedure (MacDonald et al. 1995; Shelbourne and Nitz 1992), with some
authors advocating a return to sports as early as four months post-operatively
(De Carlo et al. 1999; Howell and Taylor 1996).
There are, however, several reasons for concern about the assumption that
“aggressive” rehabilitation with a rapid return to sports is appropriate. Firstly,
studies regarding how much loading and motion a knee with a healing ACL
graft can sustain without permanently stretching the graft, disrupting the graft,
or creating failure of graft fixation are still lacking (Beynnon et al. 2002).
Secondly, despite “aggressive” rehabilitation, current protocols appear to be
insufficient in order to restore muscle size and strength after reconstruction of
the ACL, as described by a number of authors (Table 1).
28
Table 1. Summary of recent research measuring quadriceps muscle strength, thigh
circumference, and thigh muscle cross-sectional area (CSA) after ACL reconstruction.
Reference
Patients
Time after
Muscle
Thigh
Muscle CSA*
surgery
strength*
circumference*
(months)
Anderson et
45 (12
12
81
Not measured Not measured
al. 2002
women and
33 men)
Andrade et
14 men
8
67
98
Not measured
al. 2002
Arangio et al. 33 (9 women 49±7
90
98
91
1997
and 24 men)
Carter and
106
6
68 (PT), 74
Not measured Not measured
Edinger 1999
(ST), 78
(ST/G)
Järvelä et al. 86 (21
90
Not measured Not measured
84±1
2002
women and
65 men)
Keys et al.
31 (9 women 6
93
Not measured Not measured
2001
and 22 men)
Mattacola et 20 (9 women 18±10
84
Not measured Not measured
al. 2002
and 11 men)
McHugh et
102 (46
6
67
Not measured Not measured
al. 1998
women and
56 men)
Petschnig et 25 men
12
87
Not measured Not measured
al. 1998
Pfeifer and
39 (17
78
97
Not measured
14±2
Banzer 1999 women and
22 men)
Risberg et al. 60 (28
24
93
Not measured Not measured
1999
women and
32 men)
Ross et al.
50 (14
92
Not measured Not measured
29±15
2002
women and
36 men)
Sekiya et al. 107 (71
24 (range 12 78
Not measured Not measured
1998
women and
to 60)
36 men)
Urabe et al.
44 (20
12
78
98
Not measured
2002
women and
24 men
Wojtys and
25 (9 women 6/12/18
76/86/90
Not measured Not measured
Huston 2000 and 16 men)
Yoon and
24 men
68
Not measured Not measured
20±15
Hwang 2000
Østerås et al. 90 women
71
Not measured Not measured
6±2
1998
PT = patellar tendon graft, ST = semitendinosus tendon graft, ST/G = semitendinosus and
gracilis tendon graft
*Expressed as percent of the uninvolved leg
29
To make matters worse, it has been suggested that the deficits may even be
an underestimation when the contralateral limb is used for comparison
(Hiemstra et al. 2000).
With the exception of Pfeifer and Banzer (1999), no explanations as to why
it was not possible to restore muscle size and strength after ACL reconstruction
are offered by the authors mentioned in Table 1. Pfeifer and Banzer (1999)
explained the pronounced strength deficits over a long time period after ACL
reconstruction which were noted in their study as being due to insufficient
rehabilitation schedules, rather than neuromuscular deficits, since only three
from 39 patients showed force increases upon electrical stimulation above
maximal voluntary force. The authors did not, however, discuss the way in
which the rehabilitation programmes were insufficient. Nevertheless, there are at
least three possible reasons why ACL rehabilitation protocols are insufficient
when it comes to regaining muscle strength and volume (Augustsson 2002).
Firstly, it may be that current ACL protocols focus too heavily on functional
sport-specific exercises and exercises related to loading situations in everyday
life, possibly at the expense of weight training. Secondly, weight training
intensity may be too low during ACL rehabilitation in order to increase strength
and muscle volume. For instance, Risberg et al. (1999) used a rehabilitation
programme in which patients performed three sets of 15 to 30 repetitions, which
is mostly muscular endurance training. Not surprisingly, patients undergoing
ACL reconstruction required two years or more to achieve normal quadriceps
muscle performance using the protocol developed by Risberg et al. (1999). Rhea
et al. (2003) carried out a meta-analysis of 140 studies to identify the doseresponse relationship for strength training. It was concluded that training with a
mean intensity of 60% of 1 RM elicited maximal gains in untrained individuals,
whereas 80% was most effective in those who were trained. It is quite possible
that, for various reasons (e.g. physiotherapists avoiding heavy weight training by
way of precaution), ACL rehabilitation protocols generally never reach these
levels of intensity. Thirdly, it has been shown that compliance with the
programme decreases with time during ACL rehabilitation (Beynnon et al.
2002). This is unfortunate, as a considerable length of time often is necessary to
achieve training-induced hypertrophy. Indeed, increased strength performance
as a result of weight training lasting less than 20 weeks has been associated
primarily with neural adaptation rather than hypertrophy (Sale 1988). It is
therefore possible that the time patients spend on weight training is not sufficient
to induce hypertrophy during ACL rehabilitation.
Collectively, these studies indicate that current weight training protocols
during ACL rehabilitation may be insufficient in terms of strength and muscle
volume acquisition, which probably increases the risk of overuse injury or reinjury when individuals return to physically demanding work or sports. Further,
programmes and techniques used by athletes such as body builders and power
30
lifters are, arguably, far more advanced compared with weight training
performed in the clinical setting (Augustsson et al. 2003). ACL rehabilitation
protocols should therefore be further developed to optimise the exercises used
for the training of muscle volume and strength. Scientific studies of weight
training principles and methods used by athletes’ should form the basis of
rehabilitation exercise protocols.
Biomechanical studies of ACL grafts
Traditional rehabilitation programmes have been based on animal studies that
found that graft maturity is not achieved until about one year after surgery, as
the graft goes through a stage of early necrosis (DeMaio et al. 1992). Some
authors recommend jogging at four months and sports at six to nine months
when it is thought the graft has undergone sufficient maturation (DeMaio et al.
1992; Noyes and Barber-Westin 1997; Podesta et al. 1990). These
recommendations are based on animal studies. Clancy et al. (1981) found that,
in monkeys, patellar tendon reconstruction had 80% of its original strength at
one year. Yoshiya et al. (1987) showed in dogs that ultimate graft failure was
only 30% of control at 20 months. Other animal studies have shown that, at
three to four months, graft peak ultimate load is 20% to 45% of the normal
ACL, and, at 12 to 24 months, the peak load was 33% of the normal ACL
(DeMaio et al. 1992).
Other studies, however, suggest that the graft never loses its viability nor
significant strength (Kleiner et al. 1986; Rougraff et al. 1993). Kleiner et al.
(1986) demonstrated that, at three weeks after implantation, fibroblasts that
repopulated the graft had a high synthetic capability. Rougraff et al. (1993)
biopsied human autogenous patellar tendon grafts and found viability as early as
three weeks postoperatively with no stage of complete necrosis. Amiel et al.
(1983) have shown that the patellar tendon graft is immediately able to respond
to the environment. Hannafin et al. (1995) supported these results when they
demonstrated that stress had a positive influence on healing, collagen formation,
and alignment along the lines of stress for greater strength. Moreover, in a 37year-old man eight months after autogenous patellar graft, Beynnon et al.
(1997b) found that the reconstructed tendon exhibited biomechanical behaviour
superior to that found in animal studies with an ultimate failure equal to 87% of
the normal ACL.
Taken together, the limits of strain that are safe for a healing ACL graft are
not clear, and the exercises that are either safe or harmful during rehabilitation
have currently not been identified (Beynnon et al. 2002). So, the application of
findings from biomechanical studies of healing ACL grafts to the clinical
environment and the rehabilitation of a healing graft must be performed with
caution.
31
Summary of problem areas presented in the introduction
In the introduction, the objective was to discuss the often complex relationships
between various factors and to focus on some problem areas when it comes to
athletic and therapeutic training and testing.
• Current rehabilitation programmes appear to be insufficient when it
comes to restoring muscle size and strength after ACL reconstruction, as
leg strength deficits often exist one year or more after surgery (Anderson
et al. 2002; Arangio et al. 1997; Risberg et al. 1999; Witvrouw et al.
2001). As it is now customary to permit patients to return to recreational
and competitive sports six months after surgery, more attention needs to
be paid to rehabilitation protocols. Few studies have, however,
investigated the effect of various weight training regimens (closed and
open kinetic chain exercises, for example) on strength and functional
performance improvements and whether these training forms are similarly
effective, or whether they complement each other, in producing strength
and functional performance gains. This topic is addressed in Studies I and
III.
• Although closed and open kinetic chain strength tests are frequently used
to monitor the effects of rehabilitation, the ability of these tests to relate to
functional performance is not clear. Moreover, studies investigating
whether closed and open kinetic chain strength tests can be used
interchangeably, or whether they complement each other, to reflect
functional performance, are lacking in current literature. This topic is
addressed in Study II.
• Injuries often tend to occur at the end of a sporting event, when a
participant is fatigued (Dugan and Frontera 2000; Feagin et al. 1987;
Östenberg and Roos 2000). It has been our observation, however, that
current clinical tests of functional performance are typically performed
under non-fatigued conditions. This may constitute a problem when
deciding whether an individual is fully rehabilitated and fit for full sports
participation. A more realistic approach, that has yet to receive scientific
attention, might be to perform functional tests under conditions of fatigue.
This topic is addressed in Studies IV and V.
32
Aims of the investigation
Study I
To compare the effect of closed versus open kinetic chain weight training of the
thigh muscles.
Study II
To compare the ability of closed and open kinetic chain tests of muscular
strength to assess functional performance.
Study III
To investigate the effect of “pre-exhaustion” exercise on lower-extremity
muscle activation during a leg press exercise.
Study IV
To evaluate single-leg hop performance following “pre-exhaustion” exercise in
a test-retest design. Further, to investigate how fatigue influences lowerextremity joint kinematics and kinetics during single-leg hops.
Study V
To investigate the ability of a new hop test, performed under conditions of
fatigue, to determine functional deficits in patients after anterior cruciate
ligament reconstruction.
33
Subjects
Study I
Sixteen male and eight female subjects, healthy and generally physically active
with asymptomatic back, hip and knee function, volunteered to participate in the
study. The subjects were randomised into a closed and an open kinetic chain
group. Due to illness and time constraints three subjects (one male in each group
and one female in the open kinetic chain group) failed to complete the study.
The closed kinetic chain group consisted of seven male and four female
subjects. Their mean (±SD) age, body mass and height were 25±6 years, 66±11
kg and 177±11 cm respectively. The open kinetic chain group consisted of seven
male and three female subjects. Their mean (±SD) age, body mass and height
were 26±5 years, 73±12 kg and 181±10 cm respectively.
Study II
Sixteen male subjects, healthy and generally physically active with
asymptomatic back, hip and knee function, volunteered to participate in the
study. Their mean (±SD) age, body mass and height were 27±5 years, 78±9 kg
and 183±9 cm respectively.
Study III
Seventeen healthy male subjects, with a mean (±SD) age, body mass and height
of 26±4 years, 77±6 kg and 182±6 cm respectively, volunteered to participate in
the study. All the subjects were recreational weight trainers with an average
(±SD) of 5.5±4 years resistance training experience.
Study IV
Eleven male subjects, healthy and generally physically active with
asymptomatic back, hip and knee function, volunteered to participate in the first
experiment. Their mean (±SD) age, body mass and height were 27±5 years,
75±10 kg and 182±4 cm respectively. Eight healthy and generally physically
active male subjects volunteered to participate in the second experiment. Their
mean (±SD) age, body mass and height were 31±6 years, 80±6 kg and 185±4 cm
respectively.
Study V
Nineteen male patients with a unilateral ACL injury who had undergone ACL
reconstruction were recruited for this study in a consecutive manner from a
cohort of patients that had undergone reconstruction of the ACL at Sahlgrenska
University Hospital, Östra (Figure 5).
34
The descriptive data for the patients (n=19) in Study V were mean (±SD)
age, body mass and height of 28±5 years, 79±8 kg and 182±5 cm respectively.
The mean (±SD) time since surgery was 11±2 months, whereas the mean time
(±SD) between the index injury and reconstruction was 22±17 months.
253 consecutive patients who had undergone ACL
reconstruction at Sahlgrenska University Hospital, Östra
76 male patients, aged 20-35, residing in Göteborg and environs,
received a letter of information regarding the study
Contact (n=58)
29 patients
were included
19 patients
(66%) completed
the study
No contact (n=18)
16 patients (28%)
declined due to knee pain
3 patients were
excluded due to
knee pain during testing
13 patients (22%) declined
to participate of other reasons
4 patients were
excluded due to
abnormal
non-fatigued hop
symmetry
3 patients did not
complete the study
of other reasons
Figure 5. Description of the patients included in Study V.
35
Ethics
All the studies were approved by the Ethics Committee at Göteborg University.
36
Methods
Weight training
In Study I, subjects performed maximal, progressive weight training, twice a
week on non-consecutive days, for six weeks (Table 2).
The closed kinetic chain group performed a barbell squat programme,
mainly activating the quadriceps and adductor muscles of the thigh (Tesch
1993). The open kinetic chain group performed a weight machine kneeextension and hip-adduction programme, activating the quadriceps and adductor
muscles of the thigh separately (Figure 6).
TABLE 2. Weight training programmes.
Closed kinetic chain group*
Open kinetic chain group§
Barbell squat
Weight machine knee-extension
Weight machine hip-adduction
Subjects performed four sets of each exercise at 10 RM
*Two minutes’ rest allowed between sets
§One minute’s rest allowed between sets
Figure 6. The closed kinetic chain group performed a barbell squat programme (left
picture). The open kinetic chain group performed a weight machine knee-extension (right
picture) and hip-adduction programme. Photos by Roland Thomeé and Jesper
Augustsson.
37
Strength testing
An isokinetic knee-extension test (Figure 7) and a 3 RM barbell squat test were
used to evaluate the training-induced effects on strength (Study I) and to
compare the ability of closed and open kinetic chain tests of muscular strength
to assess functional performance (Study II).
The isokinetic knee-extension test was performed using a Kinetic
Communicator II dynamometer (Kin-Com, Chattecx Corp., Chattanooga, USA).
In Study III, each subject’s 10 RM was determined for a leg press exercise
(Figure 7) and a knee-extension exercise by using the maximum weight that
could be lifted for 10 consecutive repetitions. The weight lifted for each trial
was increased by 5-10 kg until failure occurred.
In Studies IV and V, each subject’s unilateral 1 RM for the right and the
left leg was determined for a knee-extension exercise by using the maximum
weight that could be lifted for one repetition.
Functional performance testing
In Studies I and II, a vertical jump test was performed with the subject standing
erect on a platform, quickly performing a countermovement and jumping for
maximal height.
In Studies IV and V, functional performance was assessed by a single-leg
hop test for distance in which the subject was instructed to stand on one leg and
to position his toes to a mark on the floor. The subject was then instructed to hop
forward as far as possible and to land on the same leg. The subject was allowed
to swing his arms freely as he jumped in Study IV, but in Study V, the patient
was instructed to hold his hands on his hips throughout the jump.
All the strength and functional tests in Study V were conducted in a blinded
Figure 7. In Studies I and II, an isokinetic knee extension test was performed using a
Kin-Com dynamometer (left picture). In Study III, each subject’s 10 RM was determined
for a leg press exercise (right picture) and a knee extension exercise. Photos by Jesper
Augustsson.
38
fashion, as patients concealed their knees by wearing elastic wraps. In this way,
the test leader (J.A.) did not know whether the involved or the non-involved leg
was being tested during a particular test session.
Electromyography (EMG)
In Study III, EMG was used to investigate the effect of pre-exhaustion exercise
on lower-extremity muscle activation during a leg press exercise. Bipolar
surface electrodes with a diameter of 9 mm (Red Dot, 3M Medica, Borken,
Germany) were placed over the bellies of the rectus femoris, vastus lateralis, and
gluteus maximus muscles using a standardised method described by Isear et al.
(1997).
A Tubigrip (Seaton Healthcare Group, Oldham, England) compression
wrap was applied to the test extremity (right leg) to maintain electrode
placement. Heavy adhesive tape was used to secure electrode placement on the
gluteus maximus muscle. All the test sites were identified and prepared by the
same investigator.
The maximal voluntary isometric activation (MVIA) procedure
EMG was recorded during MVIA for each muscle and was used as a reference
value for comparison of muscle activity with and without pre-exhaustion
exercise during the leg press exercise. Three MVIAs were performed against a
fixed resistance for each muscle. Each EMG sample included the entire MVIA
interval of four seconds’ duration. The largest RMS value of the three MVIAs
was designated the reference EMG and was used for normalisation.
The pre-exhaustion exercise procedure
Subjects were placed in the knee-extension and leg press station (Figure 8).
Subjects performed one set of pre-exhaustion exercise of the quadriceps
muscles to the point of fatigue using the knee-extension exercise at a load of 10
RM. Immediately after that exercise, EMG was recorded from the rectus
femoris, vastus lateralis and gluteus maximus muscles simultaneously during
one set of the leg press exercise performed at a load of 10 RM. After a 20minute rest period, EMG was recorded as subjects once again performed one set
of the leg press exercise (without pre-exhaustion exercise) at a load of 10 RM.
Subjects terminated the exercise sets on the completion of 10 RM or muscle
failure.
39
Figure 8. Testing setup: in Study III, subjects performed a knee extension exercise (preexhaustion), immediately followed by a leg press exercise. Both exercises were
performed at a 10 RM load.
40
Hop testing under fatigued conditions
In Studies IV and V, hop performance was compared in two standardised test
conditions—non-fatigued and immediately following pre-exhaustion exercise of
the quadriceps muscle at different percentages of 1 RM strength (Figure 9).
Biomechanical analysis
For the second experiment in Study IV, a biomechanical analysis of maximal
single-leg hops during fatigued and non-fatigued conditions, the same test
protocol was used as for the first experiment.
Figure 9. Testing set-up: in Study V, the patients performed unilateral pre-exhaustion
exercise of the quadriceps muscle until failure using a variable resistance kneeextension machine at a load of 50% of 1 RM, followed by a single-leg hop.
41
Statistical methods
Study I
Student’s t-test for independent groups was used to compare the difference in
scores between groups, while a paired t-test was used for pre-post comparisons
within groups. Means and standard deviations were calculated for all variables,
except physical activity (ordinal) where median and interquartile range were
computed. Additionally, the Mann-Whitney U test was used to compare the
physical activity level of subject groups.
Study II
To examine the relationship between the values of the closed and open kinetic
chain tests of muscular strength with the test of functional performance, Pearson
product-moment correlation coefficients were determined. Relationship
differences between the closed and open kinetic chain tests of muscular strength
variables were then computed using a two-tailed t-test for testing differences
between two dependent correlation coefficients (Guilford and Fruchter 1973).
Study III
Muscle activation amplitude obtained during the pre-exhaustion exercise
procedure was normalised relative to the MVIA (test electromyograph
amplitude/electromyograph amplitude of MVIA multiplied by 100). A pairedsamples t-test was used to compare the average RMS values collected during the
leg press exercise with and without pre-exhaustion exercise. The number of
repetitions of the leg press exercise performed by subjects with and without preexhaustion exercise was compared using a paired-samples t-test.
Study IV
For the first experiment, the intraclass correlation (ICC) coefficient was
computed for the analysis of test-retest reliability under different hop test
conditions, according to Shrout and Fleiss (1979). The Friedman test was used
to determine differences in hop performance between fatigued and non-fatigued
hop test conditions. Differences between the number of hop trials and kneeextension repetitions performed at test and retest were computed using the
Wilcoxon signed-rank test. For the second experiment, comparisons between the
biomechanical variables that were obtained were made with the Friedman test.
42
Study V
Based on a hypothesised 5-10% difference in performance between hop-test
conditions using the involved and non-involved leg, the number of patients
required to achieve a power of 0.90 was estimated by power analysis.
The intraclass correlation (ICC) coefficient was computed for analyses of
the test-retest reliability of the 1 RM test, according to Shrout and Fleiss (1979).
Differences in performance between fatigued and non-fatigued hop-test
conditions for the involved and the non-involved side, and differences between
the number of hop trials and knee-extension repetitions, were analysed using
paired t-tests.
The significance was considered at the α level of P<0.05 in all studies.
43
Summary of the papers
Study I: Weight training of the thigh muscles using closed vs. open
kinetic chain exercises: a comparison of performance enhancement.
Introduction: Resistance training is commonly used in sports, for prevention of
injuries and in rehabilitation. The purpose of this study was to compare closed
versus open kinetic chain weight training of the thigh muscles and to determine
which mode resulted in the greatest performance enhancement.
Methods: Twenty-four healthy subjects were randomised into a barbell squat or a
knee-extension and hip-adduction variable resistance weight machine group and
performed maximal, progressive weight training twice a week for six weeks. All
the subjects were tested prior to training and at the completion of the training
period. A barbell squat 3 RM, an isokinetic knee-extension, and a vertical jump
test were used to monitor the effects of training.
Results: Significant improvements were seen in both groups in the barbell squat 3
RM test. The closed kinetic chain group improved by 23 kg (31%), which was
significantly more than the 12 kg (13%) seen in the open kinetic chain group. In
the vertical jump test, the closed kinetic chain group improved significantly, five
cm (10%), while no significant changes were seen in the open kinetic chain group
(test of differences across groups was not significant). A large increase in training
load was observed in both subject groups; however, improvements in isotonic
strength did not transfer to the isokinetic knee-extension test.
Conclusion: The results may be explained by neural adaptation, weight training
mode and specificity of tests.
Study II: Ability of closed and open kinetic chain tests of muscular
strength to assess functional performance.
Introduction: The purpose of this study was to investigate the ability of closed
and open kinetic chain tests of muscular strength to assess functional
performance.
Methods: Sixteen healthy male subjects, with a mean (±SD) age, body mass and
height of 27±5 years, 78±9 kg and 183±9 cm respectively, volunteered to
participate in the study. In the closed kinetic chain test (involving muscles
working across multiple joints), the subjects performed a 3 RM barbell squat. The
open kinetic chain test (involving muscles working across a single joint) consisted
of a concentric isokinetic knee-extension at an angular velocity of 60°/sec and
was performed using a Kinetic Communicator II dynamometer. The test of
44
functional performance (vertical jump) was performed with the subject standing
erect, quickly performing a counter-movement jump for maximal height.
Results: Moderately strong correlations between the test of functional
performance and the closed and open kinetic chain tests of muscular strength
were noted, r=0.51 and r=0.57, respectively (P<0.05). A correlation of r=0.64
was obtained between the closed and the open kinetic chain test of muscular
strength (P<0.01) (Figure 10).
Conclusion: It is suggested that the effect of training or rehabilitation
interventions should not be based exclusively on tests of muscular strength.
Instead, various forms of dynamometry including functional performance tests
could be recommended.
r = 0.64
(41%)
r = 0.51
(26%)
r = 0.57
(32%)
Figure 10. The correlations between the test of functional performance and the closed
and open kinetic chain tests of muscular strength. In parentheses the coefficient of
determination (r2) values are shown: open kinetic chain knee extension strength, for
example, accounted for 32% of jumping performance.
45
Study III: Effect of pre-exhaustion exercise on lower-extremity muscle
activation during a leg press exercise.
Introduction: The purpose of this study was to investigate the effect of preexhaustion exercise on lower-extremity muscle activation during a leg press
exercise. Pre-exhaustion exercise, a technique frequently used by weight trainers,
involves combining a single joint exercise, followed immediately by a related
multijoint exercise (e.g. a knee-extension exercise followed by a leg press
exercise).
Methods: Seventeen healthy male subjects performed one set of a leg press
exercise with and without pre-exhaustion exercise, which consisted of one set of a
knee-extension exercise. Both exercises were performed at a load of 10 RM.
EMG was recorded from the rectus femoris, vastus lateralis and gluteus maximus
muscles simultaneously during the leg press exercise. The number of repetitions
of the leg press exercise performed by subjects with and without pre-exhaustion
exercise was also documented.
Results: The activation of the rectus femoris and the vastus lateralis muscles
during the leg press exercise was significantly less when subjects were preexhausted (P<0.05). No significant EMG change was observed for the gluteus
maximus muscle (Figure 11). When in a pre-exhausted state, subjects performed
significantly (P<0.001) fewer repetitions of the leg press exercise.
Conclusion: Our findings do not support the popular belief of weight trainers that
performing pre-exhaustion exercise is more effective in enhancing muscle activity
compared with regular weight training. Conversely, pre-exhaustion exercise may
have disadvantageous effects on performance, such as decreased muscle activity
and a reduction in strength, during multijoint exercise.
46
Rectus femoris
110
100
%MVIA
90
**
80
70
60
50
Test 2
Vastus lateralis
*
110
100
%MVIA
90
80
70
60
50
Test 2
Gluteus maximus
110
100
%MVIA
90
80
NS
70
60
50
Test 2
Pre-ex
Pre-exhaustion
No pre-ex
No
pre-exhaustion
Figure 11. Mean and SEM of EMG activity (expressed as percent of maximal voluntary
isometric activation) during a leg press exercise with compared to without preexhaustion exercise for the rectus femoris, vastus lateralis, and gluteus maximus
muscles, respectively. *Indicates difference (p=0.034) from pre-exhausted condition.
**Indicates difference (p=0.001) from pre-exhausted condition.
47
Study IV: Development of a single-leg hop test performed under
fatigued conditions using pre-exhaustion exercise: reliability and
biomechanical analysis.
Introduction: A pre-exhaustion exercise protocol was combined with single-leg
hop testing to improve the possibilities to evaluate the effects of training or
rehabilitation interventions.
Methods: In the first test-retest experiment, 11 healthy male subjects performed
two trials of single-leg hops under three different test conditions: non-fatigued
and following pre-exhaustion exercise which consisted of unilateral weight
machine knee-extensions until failure occurred at 80% and 50% respectively, of 1
RM strength. For the second experiment, eight healthy male subjects performed
the pre-exhaustion exercise protocol to investigate how fatigue influences lowerextremity joint kinematics and kinetics during single-leg hops. Hip, knee and
ankle joint angles, moments and powers, as well as ground-reaction forces were
recorded with a six-camera, motion-capture system and a force platform. The
recovery of hop performance following the fatiguing exercise was also measured.
Results: ICC coefficients ranged from 0.75 to 0.98 for different hop test
conditions (measured as maximal hop length), indicating that all the tests were
highly reliable. During the take-off for the single-leg hops, hip and knee flexion
angles, generated powers for the knee and ankle joints, and ground-reaction forces
decreased for the fatigued hop conditions compared with the non-fatigued
condition (P<0.05) (Figure 12). Compared with landing during the non-fatigued
condition, hip moments and ground-reaction forces were lower for the fatigued
hop conditions (P<0.05). Absorbed power was two to three times greater for the
knee than for the hip and five to ten times greater for the knee than for the ankle
during landing for all test conditions (P<0.05). Most measured variables had
recovered three minutes post-exercise.
Conclusion: It is concluded that the pre-exhaustion exercise protocol combined
with single-leg hop testing was a reliable method for investigating functional
performance under fatigued test conditions. Further, subjects utilised an adapted
hop strategy which employed less hip and knee flexion and generated powers for
the knee and ankle joints during take-off, as well as less hip joint moments during
landing under fatigued conditions. The large negative power values observed at
the knee joint during the landing phase of the single-leg hop, during which the
quadriceps muscle activates eccentrically, indicate that not only hop distance but
also the ability to perform successful landings should be investigated when
assessing dynamic knee function.
48
Nonfatigued
100
40
20
0
0
0,2
0,4
0,6
0,8
1
60
40
20
0
1,2
-20
4
0,4
0,6
0,8
1
1,2
Hip
Knee
Ankle
3
2
Moment (Nm)
Moment (Nm)
2
1
0
0
0,2
0,4
0,6
0,8
1
1,2
1
0
-1
-2
0
0,2
0,4
0,6
0,8
1
1,2
-2
-3
-3
25
25
Hip
Knee
Ankle
15
10
5
0
v
-5 0
0,2
0,4
0,6
0,8
1
1,2
Hip
Knee
Ankle
20
15
10
Power (W)
20
Power (W)
0,2
4
Hip
Knee
Ankle
3
5
0
-5 0
-10
-10
-15
-15
-20
-20
-25
-25
0,2
0,4
0,6
0,8
1
1,2
2000
2000
Fx
Fy
Fz
1500
Fx
Fy
Fz
1500
1000
Force (N)
1000
Force (N)
0
-40
-40
-1
Hip
Knee
Ankle
80
Flexion Angles (°)
60
-20
100
Hip
Knee
Ankle
80
Flexion Angles (°)
Fatigued
500
500
0
0
0
0,2
0,4
0,6
-500
0,8
1
0
1,2
0,2
0,4
0,6
0,8
1
1,2
-500
-1000
-1000
Time (sec)
Time (sec)
Figure 12. Representative hip, knee and ankle joint angles, moments and powers, as
well as ground-reaction forces during the take-off for a single subject for non-fatigued
and fatigued (50% of quadriceps muscle 1 RM-strength) hop conditions. The vertical
dotted lines indicate the time of take-off when the subject becomes airborne.
49
Study V: Ability of a new hop test to determine functional deficits
after anterior cruciate ligament reconstruction.
Introduction: The aim of this study was to investigate the ability of a new hop
test, performed under conditions of fatigue, to determine functional deficits after
anterior cruciate ligament (ACL) reconstruction. The test consists of a preexhaustion exercise protocol combined with a single-leg hop.
Methods: Nineteen male patients with ACL reconstruction (mean time after
operation 11 months) who exhibited normal single-leg hop symmetry values
(≥90% compared with the non-involved extremity) were tested for 1 RM
strength of a knee-extension exercise. The patients then performed single-leg
hops following a standardised pre-exhaustion exercise protocol, which consisted
of unilateral weight machine knee-extensions until failure at 50% of 1 RM.
Results: Although no patients displayed abnormal hop symmetry when nonfatigued, 68% of the patients showed abnormal hop symmetry for the fatigued
test condition. Sixty-three per cent exhibited 1 RM strength scores of below
90% of the non-involved leg. Eighty-four per cent of the patients exhibited
abnormal symmetry in at least one of the tests (Figure 13).
Normal
Hop
(nonfatigued)
Abnormal
100
Hop (fatigued)
32
1 RM strength
37
All three tests
16
0
25
50
75
100
%
Figure 13. Results of the tests of functional ability and 1 RM knee-extension strength in
Study V. Values shown are percentages of patients with ACL reconstruction within the
normal range.
50
Conclusion: Our findings indicate that patients are not fully rehabilitated 11
months after ACL reconstruction. The pre-exhaustion exercise protocol
combined with the single-leg hop test improved testing sensitivity when
evaluating lower-extremity function after ACL reconstruction. For a more
comprehensive evaluation of lower-extremity function after ACL reconstruction,
it is therefore suggested that functional testing should be performed both under
non-fatigued and fatigued test conditions.
51
Discussion
Kinetic chain weight training and strength assessment (Studies I, II
and III)
In Study I, six weeks of closed kinetic chain weight training resulted in larger
improvements in a 3 RM barbell squat test than did open kinetic chain weight
training. Although the closed kinetic chain group improved their jumping
ability, there was no difference across groups. No changes were seen in subject
groups in the isokinetic knee-extension test. The results may be explained by
neural adaptation, weight training mode and specificity of tests.
In Study I, the increase in training load (50% and 100% respectively for the
closed and the open kinetic chain group) during six weeks of weight training
was different and it could be theorised that single joint weight machine exercise
produces greater gains in training load in short-term weight training programmes
compared with multijoint free weight exercise. This is in accordance with
Chilibeck et al. (1998) who performed a resistance training study in which
prolonged neural adaptation using multijoint exercise was noted, which may
have delayed hypertrophy. One reason for this may be that, initially, highintensity training may be difficult due to high demands relating to co-ordination
and technique. Conversely, with less complex single joint exercise, early gains
in strength were accompanied by muscle hypertrophy and, presumably, faster
neural adaptation (Chilibeck et al. 1998). Moreover, McBride et al. (2003)
reported that 12 weeks of single joint weight training promoted significantly
greater percentage strength gains compared with multijoint weight training.
Taken together, it appears that neural adaptation and, as a result, hypertrophy,
may occur earlier with single joint exercises than with multijoint exercises. It
therefore appears as if the time course for the adaptation of the muscular system
is different depending on whether multijoint or single joint resistance exercise is
used (Figure 14).
It is generally believed that high forces which activate both high- and lowthreshold motor units are essential for muscle growth to occur during weight
training (Kraemer et al. 1998). Accordingly, in Study I, subject groups
performed high-intensity weight training (exercise sets were performed at a load
of 10 RM, which approximates 80% of 1 RM). However, Takarada et al.
(2000a) reported increases in muscle strength and cross-sectional area in a group
of novice, older women after low-intensity resistance training (50% of 1 RM),
combined with vascular occlusion. The improvements in muscle strength and
cross-sectional area were greater than in a group that performed low-intensity
resistance training alone and comparable to a group that followed a highintensity resistance training protocol (80% of 1 RM). Another study by Takarada
52
Single-joint exercise
High-intensity
training possible
Short phase of
neural adaptation
Early gains in strength
and hypertrophy
High-intensity
training more difficult
Prolonged phase of
neural adaptation
Delayed hypertrophy
and strength gains
Weight training
Multijoint exercise
Figure 14. Diagram showing the possible time course for the adaptation of the muscular
system depending on whether multijoint or single joint weight training is performed.
et al. (2002b) reported that, in highly trained athletes, low-intensity resistance
exercise caused an increase in muscle size, strength and endurance, when
combined with vascular occlusion. Moreover, two studies have shown
promising results for the vascular occlusion technique after reconstruction of the
ACL (Ohta et al, 2003; Takarada et al. 2000b). Takarada et al. (2000b) reported
that vascular occlusion, without being combined with any exercise, diminished
the post-operation disuse hypotrophy of knee extensors in patients who
underwent ACL reconstruction. Ohta et al. (2003) compared the effects of lowload resistance training with moderate restriction of blood flow with traditional
postoperative rehabilitation after reconstruction of the ACL. A significant
increase in leg strength and thigh muscle cross-sectional area was noted in the
experiment group as compared with the control group.
Taken together, it appears that high-intensity weight training, such as the
protocol used in Study I, may not be necessary if the goal is to obtain increases
in strength and muscle volume. In fact, low-intensity training combined with
vascular occlusion may augment strength and muscle size normally only
associated with high-intensity training (Takarada et al. 2000a). It is important to
realise, however, that traditional high-intensity training has more potential for
strengthening the passive structures of muscle-tendon units and ligaments, for
example. This is a valuable aspect of weight training when it comes to assisting
in the prevention of and rehabilitation from injury. Patients are, however, often
53
not able to advance to high-intensity weight training, even after extensive
periods of rehabilitation (due to pain, for example) and, as a result, they
frequently suffer from muscular hypotrophy. One possible solution to this
dilemma could be for the patient to perform low-intensity weight training,
combined with vascular occlusion. We are currently performing research in this
area at our laboratory.
In Study II, we investigated the ability of closed and open kinetic chain
tests of muscular strength to assess functional performance. Moderately strong
correlations were noted between the test of functional performance and the
closed and open kinetic chain tests of muscular strength, r=0.51 and r=0.57
respectively (P<0.05). A correlation of r=0.64 was obtained between the closed
and the open kinetic chain test of muscular strength (P<0.01). This correlation
(r=0.64) indicates that closed and open kinetic chain tests of strength
complement each other in their ability to assess functional performance.
In Study III, we showed that pre-exhaustion exercise had exactly the
opposite effect on muscle activation to that suggested by weight trainers using
this technique. In our study, pre-exhaustion exercise (a single joint kneeextension exercise) resulted in a reduction rather than an increase in the
activation of the quadriceps muscle during a multijoint leg press exercise.
Subjects also performed fewer repetitions of the leg press exercise when in a
pre-exhausted state. It thus appears that the pre-exhaustion technique may not
enhance muscle volume and strength more effectively, compared with regular
weight training, as suggested by weight trainers using this technique (Kamali
2001). The negative result of Study III was unfortunate, because there is a need
for effective methods of restoring quadriceps muscle strength and size after
ACL reconstruction, for example.
Although advocates of pre-exhaustion exercise have proposed this
technique in order to stimulate more muscle growth (Darden 1983), Study III is
to our knowledge the first study of the effect of pre-exhaustion exercise on
muscle activation and performance. Studies of the effect of exercise order during
a particular weight training session (that is, multijoint exercises, such as squats,
being placed at the end of the workout compared with multijoint exercises being
placed at the beginning of the workout), have, however, previously been
performed. Sforzo and Touey (1996) investigated the significance of performing
multijoint exercises during the first part of a workout and vice versa. It was
determined that when multijoint exercises were preceded by single joint
exercises, the total training volume was significantly lower compared with when
multijoint exercises were followed by single joint exercises. The findings noted
by Sforzo and Touey (1996) thus support the results of Study III, which indicate
that performing single joint exercises first, followed by multijoint exercise,
appears to be less effective in producing strength and muscle size gains. To date,
however, no training studies have been performed on the effects of pre54
exhaustion exercise. As a result, the possibility that pre-exhaustion exercise
could result in greater gains in muscle strength or hypertrophy than regular
weight training during long-term weight training cannot be ruled out.
Functional performance testing (Studies IV and V)
The aim of Study IV was firstly to develop and to examine the reliability of a
single-leg hop test performed under standardised, fatigued conditions using preexhaustion exercise and, secondly, to obtain biomechanical information about
the effect of quadriceps muscle fatigue on the kinetic and kinematic behaviour
of the lower-extremities during single-leg hops. For the first experiment, the
test-retest reliability of different hop-test conditions was determined. Hop
performance under all three test conditions was found to have high test-retest
reliability. We have thus developed a reliable method that is easy to perform and
record and which, in the clinical setting, can be used to compare functional
performance under different, standardised test conditions.
As for the biomechanical part of Study IV, during the take-off for the
single-leg hops, the main findings were that hip and knee flexion angles,
generated powers for the knee and ankle joints and ground-reaction forces
decreased for the fatigued hop conditions compared with the non-fatigued
condition. Compared with landing during the non-fatigued condition, hip
moments and ground-reaction forces were lower for the fatigued hop conditions.
The impact during landing resulted in powers during single-leg landing tasks
that were two to three times greater for the knee than for the hip and five to ten
times greater for the knee than for the ankle, for all test conditions. In simpler
terms: by “putting the brakes on” during the single-leg landings, the muscles
acting across the knee had to “brake” two to three times harder than the muscles
acting across the hip and five to ten times harder than the muscles acting across
the ankle.
Based on the results of Study IV, it is possible that the focus of interest
should shift from the ability to generate power during the take-off to the ability
to absorb power during landing, during single-leg testing for clinical or scientific
purposes. We therefore suggest that, in order to obtain a more comprehensive
assessment of knee function (after ACL injury or reconstruction, for example),
attention should not centre exclusively on comparisons between the hop distance
on the injured and uninjured sides but also on the ability successfully to perform
landings. Our findings are in accordance with the results of other studies (Ernst
et al. 2000; Juris et al. 1997; Webster et al. 2003) in which landing forces during
different jumps and hops were investigated in patients after ACL reconstruction.
Ernst et al. (2000) suggested that landing forces may be inadequately attenuated
following ACL reconstruction, which could expose the joint structures to injury.
Juris et al. (1997) tested the ability of patients after ACL reconstruction to both
55
produce force (maximal hop for distance) and absorb force (controlled hop, with
the requirement of keeping the foot fixed at the landing position until stable).
LSI scores revealed a greater deficit for force absorption than for force
production. The authors speculated that force absorption is a more appropriate
measure of functional capacity than force production. Finally, Webster et al.
(2003) observed differences in landing strategies after hamstring and patellar
tendon ACL reconstruction during the single-leg landing tasks. Interestingly,
patients with patellar tendon grafts demonstrated reduced knee flexion angles
and moments in the operated limb, whereas there were no differences between
limbs for patients with hamstring grafts.
To summarise, many functional tests that are used for patients after ACL
reconstruction measure the ability to generate force rather than the ability to
attenuate it. In simpler terms: during different functional tests, such as single-leg
hops, physiotherapists normally evaluate the ability of the muscles to function as
“accelerators” (during the take-off) rather than “brakes” (during landing).
Collectively, Study IV and other recent studies (Ernst et al. 2000; Juris et al.
1997; Webster et al. 2003) indicate that the ability to attenuate force (that is, the
ability of the muscles to work as “brakes”) after ACL reconstruction may be an
equally important functional outcome, particularly in relation to injury
prevention.
In Study V, we developed a new test in which hop performance was
investigated during conditions of fatigue in patients who had undergone ACL
reconstruction. We hypothesised that this method would improve the possibility
to evaluate the effects of rehabilitation interventions. We found that patients
with normal single-leg hop ability achieved poorer results using the involved leg
when performing single-leg hops in a fatigued state. The functional disability
after ACL reconstruction could therefore be better delineated by the
combination of pre-exhaustion exercise followed by a single-leg hop test, rather
than a single-leg hop test alone. The higher sensitivity of the combined preexhaustion exercise protocol and single-leg hop test may be explained by its
more demanding and thereby more discriminating nature compared with nonfatigued hop testing.
One possible reason for patients performing significantly worse using the
involved leg during fatigued single-leg hop testing is that the knee joint provides
the major energy absorption function during the landing phase of the single-leg
hop (as noted in Study IV). The task of landing during the fatigued hop
condition, using the involved leg, therefore presumably lead to great difficulties,
at both a central and a peripheral level, for patients with ACL reconstruction.
56
Limitations
In Study I, a comprehensive evaluation of the effects of training is limited by the
moderate number of subjects and by the moderate length of the weight training
period. The sample size in Study II was moderate, but for our purposes we
believed it was adequate. No definitive answers, however, regarding the exact
correlation between tests of muscular strength and functional performance could
be obtained from Study II. In Study III, we investigated the acute effects of preexhaustion exercise on muscle activation during a leg press exercise. It is
possible that a long-term weight training study of the effect of pre-exhaustion
exercise may have produced another outcome. In Study IV, the number of
subjects was moderate and caution should therefore be exercised when
generalising this data to apply to the general population. However, we believe
the conclusions drawn in this study are on a par with the number of subjects. In
Study V, the number of patients was moderate; however, sample size was
determined using a power analysis.
57
Conclusions
• Six weeks of closed kinetic chain weight training resulted in larger
improvements in a 3 RM barbell squat test than did open kinetic chain
weight training. No significant changes were seen in subject groups in the
isokinetic knee-extension test. The results may be explained by neural
adaptation, weight training mode and specificity of tests.
• The moderate correlations between tests of muscular strength and the
vertical jump test indicate that the results of strength measurements
cannot fully assess functional performance. Consequently, it is suggested
that the effect of training or rehabilitation interventions should not be
based exclusively on tests of muscular strength. Instead, various forms of
dynamometry including functional performance tests could be
recommended.
• Despite the widespread use of pre-exhaustion exercise by weight trainers
as a technique to increase the activation of the targeted (fatigued) muscle
during multijoint exercise, pre-exhaustion exercise may have
disadvantageous effects on muscle performance, such as reduced
activation of the fatigued muscle. Moreover, subjects performed fewer
repetitions of the leg press exercise when in a pre-exhausted state. Our
data therefore indicate that weight trainers using this method should
reconsider its effectiveness when it comes to producing strength and
muscle size gains.
• The pre-exhaustion exercise protocol combined with single-leg hop
testing may improve the possibilities to evaluate the effects of training or
rehabilitation interventions, as it permits the examination of lowerextremity muscle function under conditions of fatigue. The large negative
power values observed at the knee joint during the landing phase of the
single-leg hop, during which the quadriceps muscle activates
eccentrically, indicate that not only hop distance but also the ability to
perform successful landings should be investigated when assessing
dynamic knee function.
• The pre-exhaustion exercise protocol combined with the single-leg hop
test improved testing sensitivity when evaluating lower-extremity
function after ACL reconstruction. For a more comprehensive evaluation
of lower-extremity function after ACL reconstruction, it is therefore
suggested that functional testing should be performed under both nonfatigued and fatigued test conditions.
58
In summary
From the studies in this thesis, it is concluded that both closed and open kinetic
chain training and testing of the lower-extremity can be recommended for sports
and rehabilitation purposes. For a more realistic approach, when it comes to the
functional performance testing of patients after ACL reconstruction, it is
suggested that these tests should be performed both under non-fatigued and
fatigued test conditions.
59
Clinical relevance
Despite being a difficult and complex task, maximal restoration of lowerextremity muscle function and functional performance, and thereby protection of
the reconstructed ligament, should be a goal for the clinician and the patient
after ACL reconstruction. In Study V, 68% of the patients displayed abnormal
single-leg hop symmetry for the fatigued test condition, whereas 63% exhibited
reduced quadriceps strength, 11 months after surgery. With these muscle
function deficits in mind, several clinical questions need to be addressed,
including the return to strenuous activities and sports participation. Many
rehabilitation programmes suggest running, jumping, and twisting activities, as
early as six months after the reconstruction. At this time, it is not possible to say
how effective the knee muscles can be in attenuating impact forces and
protecting ligaments after ACL reconstruction, if muscle performance is reduced
to 70%, for example. As a result, there is clearly a need for more effective
strengthening programmes for the lower-extremity muscles during rehabilitation
after ACL reconstruction. Some of the most important variables in a programme
of this kind include: 1) progression in the weight training protocol used; 2) the
performance of both closed and open kinetic chain exercises; 3) the sequencing
of the exercises to optimise the quality of the exercise intensity (multijoint
exercises before single joint exercises) and 4) training intensity corresponding to
at least 8–12 RM.
60
The future
Several questions have arisen during the study process and should lead to future
studies.
• On the study of weight training: what is the optimal frequency, exercise
intensity and training volume for optimal strength and muscle gains?
• On the study of strength assessment: what is the correlation between
different tests of strength and power and athletic performance and to what
extent are these tests sensitive to the effects of training?
• What is the effect of a reversed pre-exhaustion strategy, i.e. preexhausting small synergistic muscles rather than prime mover agonistic
muscles?
• In what way are the kinetics and kinematics during functional tests, other
than single-leg hops, influenced by muscle fatigue?
• If functional exercises are performed late in the training sessions (that is,
in a fatigued state) during rehabilitation, is it possible to improve the
ability to develop maximal power (single-leg hop or vertical jump ability,
for example) in a fatigued state after ACL reconstruction?
61
Abstract in Swedish
Syftet med dessa studier var att få ökad kunskap när det gäller fysisk
prestationsförmåga hos friska personer och hos patienter med en opererad
ligamentskada i knäleden. Vi redovisar resultat som handlar om träning i så
kallad sluten och öppen rörelsekedja, vilka effekter man får av styrketräning och
hur man på olika sätt kan mäta muskelstyrka. Dessutom har vi utvecklat ett nytt
funktionellt test som utförs när en person är uttröttad.
I Studie I tittade vi på effekten av styrketräning i sluten rörelsekedja
jämfört med öppen rörelsekedja på muskelstyrka och funktionell
prestationsförmåga. Sammanfattningsvis visade vår studie att sex veckors
styrketräning enligt sluten rörelsekedja resulterade i större förbättringar av
benstyrka jämfört med träning i öppen rörelsekedja.
I Studie II testade vi hur väl ett test av muskelstyrka enligt sluten respektive
öppen rörelsekedja kunde bedöma funktionell prestationsförmåga (i form av ett
hopptest). Resultatet visade ett ganska starkt samband mellan hoppförmåga och
de två testen av muskelstyrka. Vi tycker därför att mätning skall utföras av
muskelstyrka i såväl sluten som öppen rörelsekedja och med test av funktionell
prestationsförmåga när effekten av träning eller rehabilitering ska bedömas.
I Studie III undersökte vi effekten av att kombinera styrketräning i sluten
och öppen rörelsekedja genom så kallad ”föruttröttning”. Erfarna styrketränare
anser att föruttröttning vid styrketräning gör att musklerna arbetar i högre grad
jämfört med när muskeln inte är föruttröttad. Aktiviteten i musklerna var dock
mindre vid föruttröttning. Resultat av studien gör att vi ifrågasätter teorin att
föruttröttning ger ett bättre träningsresultat vid styrketräning.
I Studie IV kombinerades föruttröttningsmetoden som vi undersökte i
Studie III med ett enbenshopp för att försöka förbättra möjligheterna att
utvärdera effekterna vid träning och rehabilitering. Vi såg att mätfelet var lågt
när 11 friska deltagare utförde hoppen dels i utvilat och dels i uttröttat tillstånd.
Dessutom undersökte vi på vilket sätt uttröttning av lårmuskulaturen påverkade
ledrörelser och krafter i höft-, knä- och fotled. Den bromsande kraften vid
landning var två till tre gånger större för knäleden jämfört med höftleden och
fem till tio gånger större jämfört med fotleden, både när deltagarna var utvilade
och uttröttade.
I Studie V undersökte vi förmågan hos ett nytt hopptest, som gjordes under
uttröttade förhållanden, att upptäcka brister hos patienter med en opererad
ligamentskada i knäleden. Fastän att alla patienterna hade bra hoppförmåga med
sitt opererade ben när de var utvilade, så hade två tredjedelar dålig hoppförmåga
när de var uttröttade. Alltså gav uttröttningen, kombinerat med ett enbenshopp,
62
ett bättre svar på hur duktiga patienterna egentligen var att hoppa med sitt ben
efter operationen.
Sammanfattningsvis kan man säga att fastän mätningar av muskelstyrka är
viktiga för att se effekten vid träning och rehabilitering, så kunde
styrkemätningar inte fullt ut bedöma en persons funktionella prestationsförmåga.
Brister i hoppförmåga efter en opererad ligamentskada i knäleden blev mer
uppenbara när hopptestet utfördes när patienten var uttröttad. För att på ett bättre
sätt upptäcka brister i förmåga efter en opererad ligamentskada föreslår vi därför
att hopptest ska göras dels när patienten är utvilad och dels när patienten är
uttröttad.
63
Acknowledgements
I would like to express my sincere gratitude to everyone who has made this
thesis possible.
My three mentors:
Roland Thomeé, for your brilliance, comradeship and unfailing kindness. Thank
you for your excellent guidance into the world of science, and for teaching me
what hard work and dedication can accomplish in life
Jon Karlsson, for your encouragement, perpetual optimistic view of my work,
and personal support
Gunnar Grimby, for your dedication and enthusiasm in relation my work. I will
always remember you for your intellectual intensity and capacity when it came
to analysing my work
Ulla Svantesson, for being a good room-mate for many years and for interesting
scientific discussions
Anders “Ove” Esko, co-author, but these days 100% musician, for scientific
discussions and drum lessons
Roy Tranberg, co-author, for excellent work on Study IV. Thank you for
patiently teaching me the basics of biomechanics
Per Hörnstedt, Malin Folkesson, Jens Lindblom, and Christer Lindén, coauthors, for your contribution during this work
Katharina Stibrant Sunnerhagen, for encouragement, support and sound advice
concerning my work
Carin Willén, for support and stimulating scientific discussions
Jane Carlsson, for introducing me to the world of science and for your
constructive criticism when it comes to my work
Elisabeth Larson, for encouragement and support
Åsa Cider, for your support through the years
Ninni Sernert, for your careful review of my studies
Bengt I Eriksson, for valuable discussions regarding my work
Gunnar Ekeroth, Claes Ekman and Lena Nordholm, for your assistance with the
64
statistical analysis
Jessica Bolgert Ehrnborg, Alexander Gustavsson, Karin Grävare Silbernagel,
Elin Lindh, Camille Neeter and Pia Thomeé. Thank you for friendly support and
many good times. It’s your turn now…
Mathias Wernbom, for many interesting discussions regarding weight training
principles and methods
Jurgen Broeren, for friendly support
Christer Källevåg, my friend since childhood, who inspired me to become a
physiotherapist, for kind support through the years
Colleagues and staff at SportRehab−Physical Therapy & Sports Medicine
Clinic, for enthusiastic support
Jeanette Kliger, for your excellent revision of the English text
Linda Johansson, for much kindness and for assistance in the practical matter of
preparing this thesis
Gun-Brith Åsell Otréus, for helping me with information regarding the patients
in Study V
Artur Forsberg, for your kind support through the years
Karin Larsson and Eva Runesson, for kind support
Björn Rydevik, for your kind support
Annette Dahlström, who drew all illustrations
Olle Lundgren, for supporting us with Competition Line weight training
equipment
All the subjects, for their time
My parents, Ulla Engelberg and Ture Augustsson, for their support and
understanding throughout my life
My brother Ulf Augustsson, a true “iron warrior”, who taught me the art of
weight training, for your unending support and encouragement
Rasmus and Marcus, my beloved sons, for giving me the most important things
in life ☺
My dear Sofia, for your support and love as a partner in life
Financial support:
This thesis has been supported by grants from the Swedish Centre for Research
in Sports.
65
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74
Study I
jesperAugustsson,
BSc,pr'
AndersEsko,BSc,pr2
Rolandrhomee,PhD,pr3
Ulla Svantesson,
PhD,pr4
-
ost athletes liSe resistance training involving both free weights
and weight machines
~
to improve strength
and power. The pros and cons of
training with free weights vs. weight
machines are widely discussedboth
among athletes and coaches,among
physical therapists, as weIl as in sports
science. Differences of opinion exist
as to which method would result in
optimal performance grollS.Proponents of free weights emphasize functionality and a direct application to
sporting activities (17). Conversely,
the advocators of weight machines
stresssafety and less requirements of
coordination compared with free
weight training (16). There is a similaT debate conceming the use of
closed vs. open kinetic chain lower
limb exercisesduring rehabilitation
of operativelyand conservativelymanaged injuries. A number of studies
has compared the effect of closed vs.
open kinetic chain lower limb exerciseson knee ligament strain (7,11,
13,14,29), anterior-posterior tihiofemoral translation (17), and
patellofemoral compression forces
(9). The importance of using closed
kinetic chain rehabilitation <5,20)
and evaluation (10,27) has been
stressed.However, few studies have
investigated whether the effect of
jOSPT. Volume27. NumberI. january1998
Resistancetraining is common ly used in sports for prevention of injuries and in
rehabilitation. The purpose of this study was to campare c/osed vs. oren kinetic chain weight
training of the thigh musc/esand to determine which mode resulted in the greatestperformance
enhancement. Twenty-four healthy subjects were randomized inta å barbell squat or a knee
extension and hip adduction variable resistance weight machine group and performed maximal,
progressive weight training twice a week for 6 weeks. All subjects were tested prior to training and
at the completion of the training period. A barbell squat 3-repetition maximum, an isokinetic knee
extension l-repetition maximum, and a vertical jump test were used to monitor effects of training.
Significant improvements were seen in both groups in the barbell squat 3-repetition maximum test.
The c/osed kinetic chain group improved 23 kg (31%), which was significantly more than the 12
kg (13%) seen in the oren kinetic chain group. In the vertical jump test, the c/osed kinetic chain
group improved significantly, 5 cm (10%), while no significant changes were seen in the oren
kinetic chain group. A large increase of training load was observed in both subject groups;
however, improvements in isotonic strength did not transfer to the isokinetic knee extension test.
The results may be explained by neural adaptation, weight training mode, and specificity of tests.
Key Words: resistance training, free weights, weight machines, lower extremity
1 Research
PhysicalTherapis~Departmentof RehabilitationMedicine,GöteborgUniversity,Guldhedsgatan
19, Sahlgrenska University Hospital, S-413 45 Göteborg, Sweden
2
3
4
PhysicalTherapist,Departmentof Neurology,Sahlgrenska
UniversityHospital,Göteborg,Sweden
Dean,GothenburgCollegeof HealthSciences,Departmentof Rehabilitation,Göteborg,Sweden
ResearchPhysicalTherapist,Departmentof RehabilitationMedicine, GöteborgUniversity,Sahlgrenska
UniversityHospital,Göteborg,Sweden
closed vs. open kinetic chain weight
training on str~ngth and performance is different.
When comparing free weights vs.
weight machines or closed vs. open
kinetic chain weight training, a dilemma exists in creating matching
training conditions, eg., equating total volume of training, total work,
and total training time. Moreover,
although the weight does not vary in
free weight exercise, the resistance
torque and, therefore, the required
muscular contraction, does vary according_to the mechanics of the specific exercise. Weight machines, on
the other hand, operating through,
eg., a cam, enable variable resistance
throughout the range.of motion of
an exercise. This is an attempt to approximate the strength CUIVeof the
exercise, thus forcing the muscle to
contract maximally throughout the
range of movement.
A barbell squat is a free weight,
closed kinetic chain exercise involv3
ing muscles working acrossmultiple
joints. Athletes, using resistance training, of ten include a barbell squat
program to improve lower extremity
strength. Several studies have investigated the effect of a barbell squat
exercise program on strength and
athletic performance (8,12,25).
Weight machine exercises,using muscles working across only single joints
in an oren kinetic chain, are also
commonly used to improve lower
extremity strength.
In recent years, magnetic resonance imaging is finding increased
use in basic muscle research (2,3,18).
Previous work by Tesch (23), who.
used magnetic resonance imaging
technology to investigate the thigh
muscle activity in different lower extremity weight training exercises,
identifies the quadriceps and adductor muscles as activated during a barbell squat. Likewise, activation of the
quadriceps and adductor muscles can
be attained through single joint,
weight machine exercises (23). Thus,
the purpose of this study was to comrare a 6-week training program of
closed kinetic chain barbell squatsvs.
oren kinetic chain weight machine
exercisesfor knee extension and hip
adduction regarding barbell squat
performance, isokinetic knee extension strength, and vertical jump
height.
METHOD
Subjects
Sixteen mate and eight female
students, healthy and generally physically active with asymptomatic back,
bir, and knee function, volunteered
to participate in the study. The subjects were randomized into a closed
and an oren kinetic chain group.
Due to illness and time constraints,
three subjects (one mate in each
group and Olle female in the oren .
kinetic chain group) failed to complete the study. Six subjects of the
closed kinetic chain group and five
subjects of the oren kinetic chain
group bad previous experience with
the barbell squat exercise and general weight training. The subjects'
physical activity level was registered
on a scale of 1-8 points, where 1 represented no physical activity and 8
represented engagement in competitive sports, as described by Engström
(6). Subjects gave informed consent
and were allowed to withdraw their
participation at any time during the
study. The study was approved by the
Sahlgrenska University Hospital Ethics Committee.
Testing Procedures
Subjectswere instructed and acquainted with the testing and training procedures orally and in writing
prior to initial testing. All subjects
were tested prior to training and at
the completion of the training period. Three testswere used to evaluate the effects of training: 1) a barbell squat 3-repetition maximum test,
2) an isokinetic knee extension l-repetition maximum test, and 3) a verticaljumptest.
In the barbell squat 3-repetition
maximum test, the subject made
three consecutive repetitions of lowering the maximum weight possible
until the thighs were paralIeI to the
floor and then raised the body to an
erect position with an Olympic barbell on the shoulders. The 3-repetition maximum for each subject was
determined by the ability to complete
three repetitions while maintaining
correct depth and technique of the
squat. The weight lifted was incremented by 2.5-10 kg until failure.
The second testing session,after
completion of the weight training
period, started with six repetitions at
50% of the subject's initial 3-repetition maximum result, followed by
three repetitions at 75% and 100%,
respectively. The test was then continued until failure. Two minutes of rest
was allowed between trials. A board
(2 cm thick) elevating the heels of
the subject, thus facilitating a squatting position, as weIl as a tightly wom
weight helt supporting the trunk
were mandatory. The subject was instructed to keep the back upright
with the feet at approximately 20° of
external rotation, shoulder width
apart. Olle test leader, positioned at
the side of the subject, monitored
that correct depth and technique of
the squat were maintained. The
other test leader spotted the subject
from behind, hands placed around
the waist of the subject during the lift
in caseof failure, using strong, aggressiveverbal commands and encouragement. Amirror, placed 2 m
in front of the subject, enabled visual
feedback. A safety squat rack was
used to ensure a safe performance.
Prior to testing, the subject performed a warm-up of 10 minutes of
ergometer cycling and two submaximal sets of 15 repetitions of the barbell squat. The mean number of trials performed by subject groups was
calculated. The barbell squat 3-repetition maximum test and the isokinetic
knee extension l-repetition maximum test were separated by 24-72
hours at both testing occasions.
The isokinetic knee extension
l-repetition maximum test was performed using a Kinetic Communicator II dynamometer (Kin-Com, Chattecx Corp., Chattanooga, TN). Mter
10 minutes of ergometer cycling at
50 W resistance,the subject was positioned with a hip angle of 75° of flexion in the test chair. The axis of the
knee joint was aligned with the axis
of the Kin-Com dynamometer resistance arm, and the lower leg shin
rad was secured at approximately 10
cm proximal of the lateral malleolus.
The trunk, bir, and thigh were
strapped down to ensure proper positioning and stabilization. Mter flve to
six submaximal concentric knee extensions of the right leg at an angle
velocity of 60°/sec, the subject performed three maximal trials from 90°
to 5° knee angle (0° being full knee
extension). The highest peak torque
value was documented. Olle minute
of rest was allowed between each
trial. Two subjects in the oren kinetic
Volume 27. Number 1 . January1998. JOSPT
RESEARCH
ment on both the concentric as weIl
as the eccentric phase of the exercise.
The closed kinetic chain group
performed
a barbell squat program,
* Two minutesof resta//owedbetweensets.
activating the quadriceps and adduct One minute of restal/owedbetweensets.
Subjectsperformed four sets of each exerciseat a tor muscles of the thigh (23). The
open kinetic chain group performed
ID-repetitionmaximum.
a weight machine knee extension
TABLE1. Weighttrainingprograms.
and hip adduction program, activating the quadriceps and adductor
muscles of the thigh separately.For
chain group tested their left leg because of ACL surgery and discomfort, each exercise, four sets of 8-12 repetitions were performed at a load of
respectively.A research physical therapist conducted the dynamometer
approximately 10-repetition maxi";
mum. The resistancewas progrestests, unaware of the subjects' group
sively increased during the training
affiliation. The verbal commands
were standardized during testing, and period as the subjects were instructed
to increase the training load when 10
knowledge of testing results was withrepetitions per set was attained. Rest
held until completion of all tests.
between setswas set at 2 minutes in
The vertical jump test was perthe closed kinetic chain group and l
formed with the subject standing
minute in the open kinetic chain
erect on a platform, quickly performgroup. Subjects in the closed kinetic
ing a countermovement and jumping
chain group initially performed barfor maximal height. A measuring
bell squats at approximately 75% of
tape, secured at a tightly wom helt
placed around the subject's waist, was the result of the barbell squat 3-repetition maximum test. The result of
pulled through a loop in the platthe barbell squat 3-repetition maxiform when the subject performed a
mum test was the criteria for estabverticaljump, and the height was
documented as described by Thomee lishing the initial weight load in the
open kinetic chain group and was
et al (24). Verticaljump height was
then adjusted accordingly by a minidefined as the highest value among
four trials. The test was supervised by mum of 5 kg.
To monitor strength improvethe test leaders, instructing and monments, the training load, as weIl as
itoring the subjects during all of the
the number of sets and repetitions,
trials. The vertical jump test foIlowed
was recorded by the subjects in a
directly after the isokinetic knee extraining log. The mean training load
tension l-repetition maximum test at
at the start and at the end of the
both testing occasions.
training period and the mean training sessionparticipation were calcuTraining
lated in subject groups. The level of
The subThe subjects performed maximal, supervision was set at 500/0..
jects' presence at each training sesprogressiveweight training twice a
sion was registered and the following
week on nonconsecutive dars for 6
sessionwas noted in a common calweeks (Table l). Subjectswere inendar.
structed and acquainted with the
Each training sessionbegan with
training exercisesorally and in writa warm-up of 10 minutes of ergomeing prior to the initial training sester cycling and two submaximal sets
sion. Subjectswere instructed on the
of 15 repetitions of the exercises
proper technique of each exercise,
ie., the importance of mental concen- used in their respective program. Mter the training session,the subjects
tration during the movement of the
exercise and using a controlled move- were instructed to perform stretching
jO8PT
.
Volume 27
.
Number
l
.
january
1998
STUDY
exercisesof the lower extremities.
Each sessionlasted approximately 30
minutes. Subjectswere asked to
maintain their physical activity level
during the experimental period. Two
cam-type variable resistanceweight
machines (Leg Extension FL 130 and
Hip Adductor FL 140, Competition
Line, Borås, Sweden), a safety squat
rack (Squat Rack BL 101920, Competition Line, Borås, Sweden), and an
Olympic 20-kg barbell with freeweight plates and collars (Casall,
Norrköping, Sweden) were used.
StatisticalAnalysis
Student' s t tests for independent
groups were used for comparison of
difference scores between groups,
and paired t testswere used for preand post-comparisonswithin groups.
Means and standard deviations were
calculated for all variables, except
physical activity (ordinal), where median and interquartile ranges were
computed. Additionally, the MannWhitney U test was used to campare
the physical activity level of subject
groups.
RESUL
TS
There were no significant differences between groups in physical activity level. The median score was six
in both subject groups. The interquartile range was 2 and 2.5, respectively, in the closed and the oren
kinetic chain group. There were no
significant differences between the
remaining subjects in the two groups
regarding age, height, or weight (Table 2). The resUltsobtained in the six
testing sessionsare summarized in
Table 3.
Significant improvements were
observed in both groups in the barbell squat test. The closed kinetic
chain group improved 31% (P =
0.0001), which was significantly (P =
0.0007) more than the 13% (P =
0.0001) improvement seen in the
oren kinetic chain group. No significant changeswere seen in subject
~
RESEARCH
STUDY
Ald1ough subjectswere tested on
each occasion by d1e same research
physical d1erapist, ensuring consistent
subject standardization, d1e isokinetic
knee extension test was not sensitive
to d1e large increasesof training load
(50% and 100%, respectively) ohserved in bod1 groups. This supports
d1e results of od1er studies (8,21,28)
TABLE2. Subiectcharacteristics.
where isotonic weight training
strengd1 improvements did not transgroups in the isokinetic knee extenwas 5.6 and 6.3 in the closed kinetic
fer to isokinetic movement. Measursion test: the closed kinetic chain
chain group compared with 5.5 and
ing isokinetic knee extension
group improved 5% (P = 0.3513),
4.8 in the open kinetic chain group)
strengd1 at d1e 10-repetition maxiand the oren kinetic chain group
mum would possibly more accurately
improved 2% (P = 0.5832), respecDlSCUSSION
have reflected d1e increases of traintively (P = 0.777 for test of differing load, as subjects performed sets
ences across groups). At the second
The specificity of free weight and
of 10 repetitions of d1e exercises
testing session,Olle subject of the
weight machine training is a critical
used in d1eir respective program duroren kinetic chain group experiissue, demanding accurate and sensiing d1e weight training period. The
enced pain; this result was excluded.
tive tests to prove the superiority of
velocity
of d1e exercisesperformed
The closed kinetic chain group imOlle method over another. The
during
d1e
training period was estiproved significantly in the vertical
present study incorporated three difmate
d
and,
as no speed-specificrejump test (10%, P = 0.0047) while
ferent tyres of tests to monitor the
sults
of
d1e
isokinetic
knee extension
only 7% (P = 0.0521) improvements.
effects of training, including an isowere
expected,
only
Olle
angular vewere seen in the oren kinetic chain
tonic multijoint, an isokinetic single
locity
(600/sec)
was
chosen.
The use
group (P = 0.3917 for test of differjoint and, a more functional test, the
of
velocity
spectrum
testing
is
sugences acrossgroups).
verticaljump.
gested
(26);
however,
due
to
d1e
test
Data from the training logs show
Isotonic testing such as a barbell
specificity
phenomenon
demonabout 50% improvement of the mean squat or a vertical jump, activating
strated in d1e present study, testing at
100repetition maximum strength by
the stretch-shortening cycle (15),
severalvelocities would probably not
the closed kinetic chain group and
could be argued to be more valid
about 100% improvement by the
than isokinetic testing when assessing have affected d1e results. Anod1er
oren kinetic chain group.
sporting activities; However, the isoki- possible reason for nonimprovements
in d1e isokinetic knee extension test
The closed and oren kinetic
netic knee extension test used in the
could be d1at no isokinetic training
chain group were comparable both
present study, though not activating
was performed, d1uslimiting d1e dein number of training sessions(parthe stretch-shortening cycle, has adgree of motor learning. Furd1ermore,
ticipation mean was 11.2 and 11.5,
vantagessuch as greater controlover
respectively, of a total of 12 training
as opposed to d1e barbell squat and
velocity of motion, technique, and
sessions)as weIl as in number of bar- extraneous movement, which facilid1e vertical jump test, d1e subjects
bell squat 3-repetition maximum tritates measurement reliability and obwere not aware of d1e pretraining test
als (the mean pre- and post-test trials jectivity (1).
result when performing d1e posttrain-
* Knee extension test (N = 9).
difference
(p = 0.0047).
* Intragroup difference (p = 0.0001).
t Intragroup
§ Difference
in increase between
groups (p
= 0.0007).
!ABLE 3. Resu/tsof the barbellsquatJ-repetitionmaximum,isokinetickneeextensionI-repetitionmaximum,and vertica/jump tests.
6
Volume27. Numberl. ]anuary1998.]OSPT
RESEARCH
ing test. This lack of feedback in the
form of knowledge of previous results
may to SOfie extent explain why no
group made significant glins in the
isokinetic knee extension test.
The differences in increase of
training load (50% and 100%, respectively) observed between groups
may be due to greater demands when
training with free weights. Thus, in
the closed kinetic chain group, much
time and effort was initially spent
learning proper technique. Conversely, weight machines are probably less
difficult to master, as they allow
m6vement in önly Olle plane and direction. Therefore, it is theorized
that weight machines cause greater
glins of training load in short-term
weight training programs. According
to Sale (19), increased performance
as a result of weight training lasting
less than 20 weeks is associated
mainly with neural adaptation, such
as increased motor unit activity of
prime mover muscles and improved
coordination, ie., appropriate
changes in the activation of synergists
and antagonists. It is suggestedthat
these two mechanisms may have contributed in different proportions in
subject groups in the present study.
The single joint weight machine exercises allowed a superior function of
synergistsand antagonists, enabling a
high activation of motor units in
prime mover muscles as opposed to
the complex, multijoint free weight
exercise where full motor activation
probably was more difficult to
achieve due to greater demands of
coordination. Thus, the large glins of
training load observed in the oren
kinetic chain group suggestthat the
nervous systemlearns how to use the
muscles in an optimal war more rapidly when using weight machines as
opposed to free weights.
Significant increasesin the barbell squat 3-repetition maximum test
were observed in both groups. Comparable results were reported by
Hicksonet al (12), who observed a
37% strength increase of a barbell
~quat l-repetition maximum test in
OSPT.
Volume 27. Number 1 . Tanuarv1998
six subjects after 16 weeks of a barbell squat exercise program (five sets
of 5-repetition maximum). The trainifi;g load in the study by Hickson et al
(12) was kept constant over the first
8 weeks and was then increased, as
opposed to the present study where
the resistancewas progressivelyincreased during the 6 weeks of training. Thorstensson et al (25) reported
an increased mean barbell squat
l-repetition maximum strength by
67% in 14 mate subjects after 8 weeks
of a barbell squat exercise program
(three sets of 6-repetition maximum).
These improvements (mean l-repetition maximum strength was 107 kg
before and 179 kg after the training
period) are remarkably large; however, little information of the testing
procedure was provided.
Resistancetraining has been
proven to increase motor performance tests (eg., a verticaljump) involving movement at maximal speeds
with little resistance. Colliander and
Tesch (4) observed an 8% increase
of vertical jump height in Il subjects
after a l2-week isokinetic weight
training period, which is comparable
with the 10% improvement by the
closed kinetic chain group seen in
the present study.
A comprehensive evaluation of
the effects of training in the present
study is limited by the lack of a controlgroup as weIl as by the moderate
length of the weight training period.
Moreover, although not significant,
the mean pretraining results of the
three testswere higher in the open
than in the closed kinetic chain
group. Only about every other session was supervised. Repeated testing
was not conducted; however, great
importance was attached to the standardization of the tests as weIl as the
training procedures. Further, the barbell squat test (4), the isokinetic knee
extension test (22), and the vertical
jump test (28) are proven reliable in
the literature. The number of sets
and repetitions performed by the
groups as weIl as the time of rest between setswas based on clinical expe-
STUDY
rience, with the intent of creating
matching training conditions.
More research is needed to determine the effect of different training inteIVentions on strength and
power performance as weIl as to further develop the protocols and dynamometry employed in assessment.
CONCLUSION
The present study concludes that
6 weeks of closed kinetic chain
weight training resulted in larger improvements in a b'(!.rbellsquat 3-repetitionmaximum and a vertical jump
test than did oren kinetic chain
weight training. No significant
changes were seen in subject groups
in the isokinetic kneeextension
l-repetition maximum test. The results may be' explained by neural adaptation, weight training mode, and
specificity of tests.
A large increase of training load
was observed in both subject groups;
however, improvements in isotonic
strength did not transfer to the isokinetic knee extension l-repetition
maximum test. Therefore, various
forms of dynamometry, incorporating
maTe functional performance tests,
could be recommended when designing a resistancetraining study. ]OSPT
ACKNOWLEDGMENTS
The authors acknowledge Lena
Nordholm, PhD, for her assistance
with the statistical analysis.
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.january1998. jOSPT
Study II
Scand J Med Sci Sports 2000: 10: 164–168
Printed in Denmark ¡ All rights reserved
COPYRIGHT C MUNKSGAARD 2000 ¡ ISSN 0905-7188
Ability of closed and open kinetic chain tests of muscular strength
to assess functional performance
J. Augustsson, R. Thomeé
Department of Rehabilitation Medicine, Göteborg University, Göteborg, Sweden
Corresponding author: Jesper Augustsson, MSc, PT, Department of Rehabilitation Medicine, Sahlgrenska University Hospital,
Guldhedsgatan 19, S-413 45 Göteborg, Sweden
Accepted for publication 21 December 1999
The purpose of this study was to investigate the ability of
closed and open kinetic chain tests of muscular strength
to assess functional performance. Sixteen healthy male
subjects, with a mean (∫SD) age, body mass and height
of 27∫5 years, 78∫9 kg and 183∫9 cm, respectively, volunteered to participate in the study. In the closed kinetic
chain test (involving muscles working across multiple
joints), the subjects performed a 3 repetition maximum (3
RM) barbell squat. The open kinetic chain test (involving
muscles working across a single joint) consisted of a concentric isokinetic knee extension at an angular velocity of
60æ/s, and was performed using a Kinetic Communicator II
dynamometer. The test of functional performance (vertical
jump) was performed with the subject standing erect,
quickly performing a countermovement jump for maximal
height. Moderately strong significant (P∞0.05) correlations between the test of functional performance and the
closed and open kinetic chain tests of muscular strength
were noted, rΩ0.51 and rΩ0.57, respectively. It is suggested that the effect of training or rehabilitation interventions should not be based exclusively on tests of muscular strength. Rather, various forms of dynamometry including functional performance tests could be recommended.
Today, resistance exercise training plays a vital role in
most athletic and rehabilitation programs. Except for
sports like weight lifting, power lifting, and bodybuilding where the sole purpose is to enhance muscular strength and power, it is also believed among
sports coaches and physical therapists that resistance
training will result in improvements in functional performance such as jumping, throwing or running.
Tests of muscular function are commonly performed to assess functional performance, both in the
sporting and the rehabilitation fields (Abernethy et
al. 1995). However, the relationship between tests of
muscular function and functional performance is still
not clear. Yet, tests of strength and power are often
used to monitor training-induced changes in performance or the effectiveness of rehabilitation. For
example, Østerås et al. (1998) used a rehabilitation
protocol following surgery of the anterior cruciate
ligament (ACL) where they recommended quadriceps
muscle torque force corresponding to 85% of the
muscle strength, compared with the non-operated
limb, before no restrictions needed be taken in sport
and work activities. Recent studies, however, indicate
a relatively low relationship between tests of muscle
function and dynamic performance, both in healthy
subjects (Murphy & Wilson 1997, Wilson et al. 1997)
as well as in subjects with ACL-reconstruction (Pfeif-
er & Banzer 1999). Pincivero et al. (1997) studied the
relationship between concentric isokinetic quadriceps
and hamstring strength values with the single hop for
distance, a functional activity. It was concluded that
only low to moderate significant relationships existed
between the single hop for distance and the knee
strength tests.
Currently, isometric, isokinetic and isotonic dynamometry are used to assess muscular function.
Each form has its drawbacks, the main argument
against isometric assessment being that isometric
tests bear little resemblance to the dynamic nature of
most sporting activities (Ashley & Weiss 1994). The
perceived disadvantage of isokinetic assessment is the
absence of acceleration and stretch-shortening cycle,
and that single-joint, isolated assessment often is
used, which again bears little resemblance to functional performance (Augustsson et al. 1998). Those
against isotonic assessment tend to emphasize poor
reliability and objectivity due to intersubject, intertrial and interlaboratory variations (Abernethy et
al. 1995). Regardless of which of the three modes of
dynamometry is employed, assessment can be performed using either closed or open kinetic chain
movement.
A barbell squat is a free weight, closed kinetic
chain exercise, involving muscles working across
164
Kinetic chain tests and functional performance
multiple joints. Athletes, using resistance training,
often include a barbell squat program to improve
lower extremity strength. Several studies have used a
barbell squat test to determine the effect of various
training and rehabilitation interventions (Wilson et
al. 1997, Hickson et al. 1994). Isokinetic or isotonic
testing and training such as knee extension/flexion,
using muscles working across only single joints in an
open kinetic chain, are also commonly used to evaluate and improve lower extremity strength (Thomeé et
al. 1995, Fry et al. 1991).
In recent years, the importance of using closed kinetic chain evaluation (Greenberger & Paterno 1995)
and rehabilitation (Beynnon et al. 1997) has been
stressed, due to the belief that closed as opposed to
open kinetic chain movement is more closely related
to function. Moreover, several authors suggest that
some types of open kinetic chain exercise are associated with greater anterior-posterior shear forces (Bynum et al. 1995, Yack et al. 1993) and patellofemoral
compression forces (Bynum et al. 1995) compared to
other types of closed kinetic chain exercise. However,
few studies have compared the ability of closed and
open kinetic chain tests of muscular strength to assess
functional performance. Thus, the purpose of this
study was to assess the relationship between a closed
kinetic chain test of lower extremity strength and an
open kinetic chain test of knee extensor strength with
a test of functional performance.
Method
Subjects
Sixteen male subjects, healthy and generally physically active
with asymptomatic back, hip and knee function, volunteered to
participate in the study. Their mean (∫SD) age, body mass and
height were 27∫5 years, 78∫9 kg and 183∫9 cm, respectively.
Nine subjects had previous experience of the barbell squat exercise and of general weight training. The subjects’ physical activity level was registered on a scale of 1–8 points, where 1 represented no physical activity and 8 represented engagement in
competitive sports, as described by Engström (1980). The median physical activity level score was 6 in the subject group and
the interquartile range was 2.75. The study was approved by
the Ethics Committee of the Faculty of Medicine, Göteborg
University, Sweden.
Testing procedures
Subjects were instructed and acquainted with the testing procedures orally and in writing prior to testing.
In the closed kinetic chain test, subjects performed a barbell
squat 3 repetition maximum (3 RM): three consecutive repetitions of lowering the maximum weight possible until the
thighs were parallel to the floor, and then raised to an erect
position, with an Olympic barbell on the shoulders. The 3 RM
for each subject was determined by the ability to complete 3
repetitions while maintaining correct depth and technique of
the squat. The weight lifted was incremented by 2.5–10 kg until
failure. Two minutes’ rest was allowed between trials. A board
(2 cm thick) elevating the heels of the subject, thus facilitating
a squatting position, as well as a tightly worn weight-belt supporting the trunk were mandatory. The subject was instructed
to keep the back upright with the feet at approximately 20æ of
external rotation, shoulder width apart. One testleader, positioned at the side of the subject, monitored that correct depth
and technique of the squat was maintained. The other testleader spotted the subject from behind, hands placed around the
waist of the subject during the lift in case of failure, using strong
verbal commands and encouragement. A mirror, placed 2 m in
front of the subject, enabled visual feedback. Prior to testing
the subject performed a warm-up of 10 min of ergometer cycling and two submaximal sets of 15 repetitions of barbell squat.
A safety squat rack (Squat Rack BL 101920, Competition Line,
Borås, Sweden) and an Olympic 20 kg barbell with free-weight
plates and collars (Casall, Norrköping, Sweden) were used. The
barbell squat 3 RM test and the concentric isokinetic knee extension test were separated by 24–72 h.
The open kinetic chain test (concentric isokinetic knee extension) was performed using a Kinetic Communicator II dynamometer (Chattanooga Group, Inc., P.O. Box 489, Hixson, TN
37343, USA). After 10 min of ergometer cycling at 50 W resistance, the subject was positioned with a hip angle of 75æ of
flexion in the test chair. The axis of the knee joint was aligned
with the axis of the Kin-Com dynamometer resistance arm and
the lower leg shin pad was secured at approximately 10 cm
proximal to the lateral malleolus. The trunk, hip and thigh were
strapped down to ensure proper positioning and stabilization.
After 5–6 submaximal concentric knee extensions of the right
leg at an angular velocity of 60æ/s, the subject performed 3
maximal trials from 90æ to 5æ knee angle (0æ being full knee
extension). The highest peak torque value was documented.
One minute of rest was allowed between each trial. One subject
tested his left leg because of discomfort. A research physical
therapist conducted the dynamometer tests.
The test of functional performance (vertical jump) test was
performed with the subject standing erect on a platform, quickly performing a countermovement jump for maximal height. A
measuring tape, secured at a tightly worn belt placed around
the subject’s waist, was pulled through a loop in the platform
when the subject performed a vertical jump and the height was
documented, as described by Thomeé et al. (1995). Vertical
jump height was defined as the highest value among 4 trials.
The test was supervised by the testleaders, instructing and
monitoring the subjects during all the trials. The vertical jump
test followed directly after the concentric isokinetic knee extension test.
Statistical analysis
To examine the relation between the values of the closed and
open kinetic chain tests of muscular strength with the test of
functional performance, Pearson product-moment correlation
coefficients were determined. Relationship differences between
the closed and open kinetic chain tests of muscular strength
variables were then computed using two-tailed t test for testing
differences between two dependent correlation coefficients (Guilford & Fruchter 1973). The significance was considered at the
a level of P⬍0.05.
Results
The mean (∫SD) barbell squat 3 RM strength, concentric isokinetic knee extension torque and vertical
jump height were 101∫18 kg, 241∫65 Nm and 54∫7
cm, respectively.
165
Augustsson & Thomeé
Fig. 1. Correlation between the closed kinetic chain test (3 RM barbell squat) and the open kinetic chain test (concentric isokinetic
knee extension), respectively, and the test of functional performance (vertical jump) in healthy male subjects (nΩ16) with 95%
confidence interval.
Relation between muscular strength and functional
performance tests
Moderately strong significant (P⬍0.05) correlations
between the test of functional performance and the
closed and open kinetic chain tests of muscular
strength were noted, rΩ0.51 and rΩ0.57, respectively.
Fig. 1 illustrates the correlations between closed and
open kinetic chain test scores and the test of functional performance. There was also a moderately
strong significant (P⬍0.01) correlation between the
closed and the open kinetic chain test of muscular
strength, rΩ0.64.
Closed and open kinetic chain relationship differences
When comparing the coefficients of correlation (rΩ
0.51 and rΩ0.57) between the tests of muscular
strength and functional performance, it was found
that this relationship was not significantly different
(tΩ0.70, P±0.05).
Discussion
We investigated the ability of closed and open kinetic
chain tests of muscular strength to assess functional
performance. Moderately strong significant (P⬍0.05)
correlations were noted between the test of functional
performance and the closed and open kinetic chain
tests of muscular strength, rΩ0.51 and rΩ0.57, respectively. A correlation of rΩ0.64 (P⬍0.01) was obtained between the closed and the open kinetic chain
test of muscular strength.
The fact that the closed and open kinetic chain
tests of muscular strength did not differ in regard to
their ability to predict performance probably reflects
that the quadriceps muscle is important in vertical
jumping and that, furthermore, individual quadriceps
166
muscle strength correlates with gluteus maximus
muscle and triceps surae muscle strength.
In a recent study by Blackburn & Morrissey
(1998), open kinetic chain knee extensor strength
demonstrated startlingly low correlation with vertical jump (rΩ0.01) and standing long jump (rΩ0.07)
performance, whereas Petschnig et al. (1998), who
studied the relationship between an isokinetic
quadriceps strength test and four different functional performance tests in healthy subjects and patients with surgery of the ACL, reported moderately strong correlation coefficients (between rΩ0.45
and rΩ55). In a review (Abernethy et al. 1995) of
articles where correlations between muscular
strength tests and functional performance were investigated, relationships typically ranged between
rΩ0.50 and rΩ0.93.
Östenberg et al. (1998) recently reported low correlations between isokinetic knee extensor strength and
functional tests in healthy female soccer players and
recommended not using functional performance and
isokinetic testing interchangeably. Murphy & Wilson
(1997) went even further, suggesting the effectiveness
of training or rehabilitation programs should be
based on changes in performance rather than tests of
muscular function. However, the restoring of muscle
size and strength is a cornerstone in rehabilitation,
and therefore tests of muscular function must be considered essential. In a recent study (Pfeifer & Banzer
1999), pronounced strength deficits over a long
period of time after surgery on the ACL was noted.
Likewise, Carter & Edinger (1999) were intrigued to
find only half of the competitive athletes in their
study had achieved 80% or greater leg strength of the
ACL-operated leg by six months after surgery, as it is
now customary to allow return to full activities at
that time, with some authors advocating return to
sports as early as four months after the procedure
Kinetic chain tests and functional performance
(De Carlo et al. 1999, Howell & Taylor 1996).
Carter & Edinger (1999) concluded that athletes theoretically may return to sports four to six months
postoperatively, but that frequently leg strength is not
adequate at that time to do so without running the
risk of reinjuring the knee. This is supported by Johnston et al. (1998), who investigated the effect of lower
extremity muscular fatigue on motor control performance. It was concluded that fatigued individuals
are at increased risk of injury because of loss of balance and that preconditioning may prevent injury.
Both closed and open kinetic chain testing could
under certain circumstances be considered as having
low validity. As a diagnostic test, a closed kinetic chain
movement, involving several groups of muscles working across multiple joints, is unable to determine to
what extent a particular muscle is activated. Conversely, the open kinetic chain test, because of its more
‘‘non-functional’’ nature, is able to isolate a specific
muscle and thereby detect dysfunction. Thus, the purpose of assessment should determine which mode of
dynamometry be used: to identify specific deficiencies
or problem areas, open kinetic chain testing would be
preferred, whereas a closed kinetic chain test may be
better suited for assessing functional performance.
Despite several studies (Beynnon et al. 1997, Yack
et al. 1993) concerning safety issues of closed and
open kinetic chain exercises in ACL rehabilitation,
and although some authors have advocated the sole
use of closed kinetic chain exercises (Bynum et al.
1995, Shelbourne & Nitz 1992), it is concluded that
both types of exercises can be performed in ways that
do not place excessive strain on the ACL (Fitzgerald
1997). Escamilla et al. (1998), comparing knee joint
biomechanics while performing closed and open kinetic chain weight training at a 12 RM load, reported
that peak ACL tension forces in open kinetic chain
exercise were only 0.2 times bodyweight, and nonexistent in closed kinetic chain exercise. Factors such
as joint compressive forces (e.g. axial loading) and
joint geometry probably play integral roles in knee
joint stability during closed kinetic chain exercise
(Isear et al. 1997), whereas significant coactivation of
the antagonists during maximal knee flexion/extension, indicating an inhibitory mechanism which prevents overloading of the joint and contributes to joint
stabilization (Kellis & Baltzopoulos 1998), would ex-
plain the low ACL tension forces during open kinetic
chain exercise.
There are some methodological issues to be addressed. The sample size in the present study was
moderate, but for our purposes we believed it was
adequate. No definitive answers regarding the exact
correlation between tests of muscular strength and
functional performance could be achieved from the
present study. Our results are nevertheless of importance due to the scarcity of data in the literature on
the ability of closed and open kinetic chain tests of
muscular strength to assess functional performance.
More research is needed to further improve protocols and dynamometry employed in the assessment
of training or rehabilitation interventions. A challenge for future research could be to develop tests
sensitive and specific enough to discriminate relevant
muscular and functional deficits or compensations
following, for example, ACL-reconstruction. We believe a testing procedure that combined muscular
strength with functional performance parameters
would enhance the diagnostic spectrum and provide
a more comprehensive assessment. For example,
functional performance ought to be tested under
both fatigued and nonfatigued conditions. This presumably would improve the possibilities to evaluate
and compare muscular function of the healthy and
injured leg.
In conclusion, the moderate correlations between
tests of muscular strength and the vertical jump test
indicate that the results of strength measurements
cannot be used to adequately assess functional performance. Consequently, it is suggested that the effect
of training or rehabilitation interventions should not
be based exclusively on tests of muscular strength.
Rather, various forms of dynamometry including
functional performance tests could be recommended.
Key words: barbell squat; isokinetic knee extension;
vertical jump; multi- versus isolated-joint testing; rehabilitation.
Acknowledgements
The authors acknowledge Lena Nordholm, PhD, for her assistance with the statistical analysis. We also thank Jon Karlsson,
PhD, and Gunnar Grimby, PhD, for their constructive criticism.
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Study III
Journal of Strength and Conditioning Research, 2003, 17(2), 411–416
q 2003 National Strength & Conditioning Association
Effect of Pre-Exhaustion Exercise on
Lower-Extremity Muscle Activation During
a Leg Press Exercise
JESPER AUGUSTSSON,1 ROLAND THOMEÉ,2 PER HÖRNSTEDT,3
JENS LINDBLOM,4 JON KARLSSON,2 AND GUNNAR GRIMBY,1
Department of Rehabilitation Medicine, Göteborg University, Göteborg, Sweden 41345; 2Department of
Orthopaedics, Göteborg University, Göteborg, Sweden 41345; 3Odda Physical Therapy, Odda, Norway 5750;
4
Kroppsakuten Physical Therapy, Göteborg, Sweden 42750.
1
ABSTRACT
Introduction
The purpose of this study was to investigate the effect of
pre-exhaustion exercise on lower-extremity muscle activation
during a leg press exercise. Pre-exhaustion exercise, a technique frequently used by weight trainers, involves combining a single-joint exercise immediately followed by a related
multijoint exercise (e.g., a knee extension exercise followed
by a leg press exercise). Seventeen healthy male subjects performed 1 set of a leg press exercise with and without preexhaustion exercise, which consisted of 1 set of a knee extension exercise. Both exercises were performed at a load of
10 repetitions maximum (10RM). Electromyography (EMG)
was recorded from the rectus femoris, vastus lateralis, and
gluteus maximus muscles simultaneously during the leg
press exercise. The number of repetitions of the leg press
exercise performed by subjects with and without pre-exhaustion exercise was also documented. The activation of the
rectus femoris and the vastus lateralis muscles during the
leg press exercise was significantly less when subjects were
pre-exhausted (p , 0.05). No significant EMG change was
observed for the gluteus maximus muscle. When in a preexhausted state, subjects performed significantly (p , 0.001)
less repetitions of the leg press exercise. Our findings do not
support the popular belief of weight trainers that performing
pre-exhaustion exercise is more effective in order to enhance
muscle activity compared with regular weight training. Conversely, pre-exhaustion exercise may have disadvantageous
effects on performance, such as decreased muscle activity
and reduction in strength, during multijoint exercise.
I
Key Words: alternative weight training technique, electromyography, single-joint exercise, multijoint exercise
Reference Data: Augustsson, J., R. Thomeé, P. Hörnstedt, J. Lindblom, J. Karlsson, and G. Grimby. Effect
of pre-exhaustion exercise on lower-extremity muscle
activation during a leg press exercise. J. Strength Cond.
Res. 17(2):411–416. 2003.
n the initial stages of weight training for sports or
rehabilitation purposes, increases in strength are
quite rapid, mainly because of neural adaptation (17).
In contrast, at the intermediate and advanced stages
of weight training progress is markedly slower. By
then, weight training for athletic purposes is often
characterized by performance plateaus or even decrements (3, 4). However, a number of empirically based
strategies have been developed through the years to
maintain a positive response to long-term weight
training (2, 13). Thus various systems, such as periodization (i.e., organization of training into distinct periods), and methods, such as supersets, forced reps,
power factor training, and pre-exhaustion exercise, are
used to avoid performance to plateau and for bringing
about optimal gains in strength and muscle hypertrophy (1–3, 18, 20–22).
The practice of pre-exhaustion exercise has been
made popular by Eastern European weight lifters and
by body builders in the United States (2). Pre-exhaustion exercise involves working a muscle or a muscle
group to the point of fatigue using a single-joint exercise, immediately followed by a related multijoint exercise (2, 18, 21). For example, a weight trainer might
pre-exhaust his or her quadriceps muscles by performing a knee extension exercise, then follow that exercise
immediately with either a barbell squat exercise or a
leg press exercise (2). In nonscientific weight training
literature, authors advocate this method to overcome
‘‘sticking points’’ or for ‘‘bringing a ‘weak’ body part
up to speed’’ by providing the pre-exhausted muscle
with a greater training stimulus compared with regular weight training (12).
The effects of fatigue on muscle function and the
implications of this on strength and muscle hypertrophy acquisition is not well documented, and existing
411
412 Augustsson, Thomeé, Hörnstedt, Lindblom, Karlsson, and Grimby
data on whether fatigue may stimulate strength and
muscle volume development is contradictory. Rooney
et al. (16) reported that fatiguing, continuous repetitions resulted in greater strength gains compared with
when rest was taken between repetitions. Similarly,
Schott et al. (19) demonstrated greater strength gains
and muscle hypertrophy following strength training
using long, fatiguing activations compared with short,
intermittent activations. Also, Tesch (22) noted that
body builders, who display large muscularity and
mass, must ‘‘punish themselves’’ (i.e., perform sets to
exhaustion in their training programs) in order to see
progress. Conversely, Pincivero et al. (15) examined
the influence of rest intervals on strength gains subsequent to high-intensity training and reported that a
longer rest period between sets resulted in greater improvement in muscle strength. The results obtained by
Pincivero et al. (15) is supported by the observation
that development of fatigue is not desired in power
lifting where the major training goal is to optimize
maximal strength (2). Taken together, it is still not
clear whether accumulation of fatigue during exercise
may be of importance if the objective is to bring about
maximal muscle hypertrophy and strength gains.
Although weight trainers frequently use pre-exhaustion exercise, this training technique has, to our
knowledge, not been the subject of a scientific study.
Weight trainers using this method believe pre-exhaustion exercise would result in greater muscle activation
for the subsequent multijoint exercise because presumably the pre-exhausted muscle is engaged in both exercises (12). To test this hypothesis, we decided to use
the knee extension and the leg press as test exercises
to gain a stress profile of the pre-exhaustion method
and to compare this technique to regular weight training. Thus the purpose of this study was to investigate
the effect of pre-exhaustion exercise on lower-extremity muscle activation during a leg press exercise.
Methods
Experimental Approach to the Problem
To test the hypothesis presented in the Introduction,
electromyography (EMG) was recorded from 3 lowerextremity muscles with and without pre-exhaustion
exercise (knee extensions) during the leg press exercise. The number of repetitions of the leg press exercise
performed by subjects with and without pre-exhaustion exercise was also documented. The collection of
these acute data may suggest whether pre-exhaustion
exercises have a greater potential for producing
strength and muscle size gains compared with regular
weight training.
Subjects
Seventeen healthy male subjects with a mean (6SD)
age, body mass, and height of 26 6 4 years, 77 6 6
kg, and 182 6 6 cm, respectively, volunteered to par-
ticipate in the study. All subjects were recreational
weight trainers with an average (6SD) of 5.5 6 4 years
of resistance training experience. None of the subjects
had a recent or remote history of significant lowerextremity injury. Before participation in this study,
each subject provided informed consent approved
through the Ethics Committee of the Faculty of Medicine, Göteborg University, Sweden.
Determination of 10 Repetitions Maximum
Each subject performed a pretest 4 to 5 days before
testing began. At this time the experimental protocol
was reviewed and the subjects were given the opportunity to ask questions. In addition, each subject’s 10
repetitions maximum (10RM) was determined for a
knee extension exercise and a leg press exercise by using the maximum weight that could be lifted for 10
consecutive repetitions. The weight lifted for each trial
was incremented by 5–10 kg until failure occurred.
Each subject’s knee-flexing and knee-extending cadence was not fixed during the knee extension and the
leg press exercise, rather each subject was allowed to
use a self-selected tempo while performing the exercises. Five minutes of rest was allowed between trials.
EMG Electrode Preparation
The exercise session began with EMG electrode preparation. Each electrode site was shaved, abraded, and
cleaned with alcohol to facilitate electrode adherence
and conduction of EMG signals. Bipolar surface electrodes with a diameter of 9 mm (Red Dot, 3M Medica,
Borken, Germany) were placed over the bellies of the
rectus femoris, vastus lateralis, and gluteus maximus
muscles using a standardized method described by Isear et al. (10).
A Tubigrip (Seaton Healthcare Group, Oldham,
England) compression wrap was applied to the test
extremity (right leg) to maintain electrode placement.
Heavy adhesive tape was used to secure electrode
placement on the gluteus maximus muscle. All test
sites were identified and prepared by the same investigator.
Instrumentation
The EMG signal was preamplified with a gain of
1,000, an impedance of more than 0.5 MOhm at 50 Hz,
and a band width of 0.5–400 Hz by an HDX-82 (Chattanooga Group Inc., Hixson, TN) and was thereafter
band pass-filtered between 7 and 490 Hz by a KCEMG (Chattanooga Group). The EMG was sampled
with a frequency of 1,250 Hz by an NB-MIO-16L9 (National Instruments Corporation, Austin, TX) on a Macintosh computer with software developed in Lab View
(National Instruments) by Punos Electronics AB, Göteborg, Sweden. The EMG signal was rectified and the
average of the amplitude was calculated using the root
mean square (RMS) method. During testing, RMS
EMG signals were monitored on the computer. Before
Effect of Pre-Exhaustion Exercise on Muscle Activation
Figure 1. Testing setup: Subjects performed a knee
extension exercise (pre-exhaustion) immediately followed
by a leg press exercise. Both exercises were performed at a
10 repetition maximum (10RM) load.
each testing session began, calibration of the EMG apparatus was performed according to the specifications
outlined in the manufacturer’s service manual.
The Maximal Voluntary Isometric Activation Procedure
The maximal voluntary isometric activation (MVIA)
was recorded for each muscle and was used as a reference value for comparison of muscle activity with
and without pre-exhaustion exercise during the leg
press exercise. Three MVIAs were performed against
a fixed resistance for each muscle in the following positions: the rectus femoris muscle and the vastus lateralis muscle—seated with the hip at 908 and the knee
at 608 of flexion; and the gluteus maximus muscle—
prone with the hip at 108 of extension and the knee at
more than 908 of flexion. Each activation was held for
4 seconds with a 10-second rest period between repetitions. Each EMG sample included the entire MVIA
interval of 4 seconds’ duration. The largest RMS value
of the 3 MVIAs was designated the reference EMG and
used for normalization.
The Pre-Exhaustion Exercise Procedure
Subjects were then placed in the knee extension and
leg press station (Figure 1). Before testing commenced,
each subject was instructed in the proper technique for
each exercise (i.e., the importance of mental concentration during the performance of the exercise) and using
a controlled movement for both the concentric as well
as the eccentric phase of the exercise. Warm-up consisted of 2 submaximal (not in excess of 40% of their
10RM pretest weight) sets of 10 repetitions of the knee
extension and leg press exercises.
The starting and ending positions for the knee extension exercise were seated with approximately 1208
knee flexion angle. From the starting position, each
subject extended the knees and returned to the starting position. The pad supporting the back was ad-
413
justed for each subject so that the axes of the knee
joints were aligned with the axis of the knee extension
machine resistance arm. The footpad was positioned
at approximately 5 cm proximal to the lateral malleolus.
The beginning and ending position for the leg
press was with the knee in full extension. Subjects
were assisted to the beginning position of the leg press
exercise by 1 investigator; thus in this position data
collection was initiated. In a continuous motion the
subject descended to maximum knee flexion (1208) and
then ascended back to the starting position. Visual
feedback of the 1208 knee flexion angle position for
each subject was enabled through markers, which were
attached onto the leg press machine. Subjects used a
standardized 40-cm stance width on the leg press platform, with the feet at 208 of external rotation.
Subjects performed 1 set of pre-exhaustion exercise
of the quadriceps muscles to the point of fatigue using
the knee extension exercise at a load of 10RM. Immediately following that exercise, EMG was recorded
from the rectus femoris, vastus lateralis, and gluteus
maximus muscles simultaneously during 1 set of the
leg press exercise performed at a load of 10RM. After
a 20-minute rest period, EMG was recorded as subjects
once again performed 1 set of the leg press exercise
(without pre-exhaustion exercise) at a load of 10RM.
Subjects terminated the exercise sets on the completion
of 10RM or muscle failure. One investigator monitored
the exercise to ensure that the correct technique was
maintained while using strong verbal commands and
encouragement. EMG samples were collected for all
repetitions of the leg press exercise set. The range of
motion for collecting the EMG was from 08 to 1208
knee flexion, and both the concentric and the eccentric
phases of the exercise were examined. The mean RMS
value for the leg press exercise set under each condition was then calculated. The number of repetitions of
the leg press exercise performed by subjects with and
without pre-exhaustion exercise was documented. The
order of performing the leg press exercise (with and
without pre-exhaustion exercise) was randomly assigned for subjects. Prior to testing all subjects performed a pre-exhaustion exercise procedure session for
familiarization purposes, with a minimum of 4 days
between tests.
Statistical Analyses
Muscle activation amplitude obtained during the preexhaustion exercise procedure was normalized relative
to the MVIA (test EMG amplitude/EMG amplitude of
MVIA multiplied by 100). Paired-samples t-test was
used to compare the average RMS values collected
during the leg press exercise with and without preexhaustion exercise. The number of repetitions of the
leg press exercise performed by subjects with and
without pre-exhaustion exercise was compared using
414 Augustsson, Thomeé, Hörnstedt, Lindblom, Karlsson, and Grimby
a paired-samples t-test. An alpha level of 0.05 was
used for all comparisons.
Results
Significantly lower EMG activity during the leg press
exercise set was noted for the rectus femoris (p 5
0.001) and the vastus lateralis (p 5 0.034) muscles with
pre-exhaustion exercise compared to without pre-exhaustion exercise. No significant difference of gluteus
maximus muscle activity was observed between the
pre-exhausted condition and the non–pre-exhausted
condition (p 5 0.755; Figure 2). Subjects performed
significantly (p 5 0.001) less repetitions of the leg press
exercise with compared to without pre-exhaustion exercise; the mean (6SD) number of repetitions was 7.9
(61.4) and 9.3 (62.3), respectively.
Discussion
Our study showed that pre-exhaustion exercise had
the exact opposite effect on muscle activation as suggested by weight trainers using this technique. In our
study, pre-exhaustion exercise (a single-joint knee extension exercise) resulted in decreased, rather than increased, activation of the quadriceps muscle during a
multijoint leg press exercise. Subjects also performed
less repetitions of the leg press exercise when in a preexhausted state. Thus the lower muscle activity and
reduction of strength when using pre-exhaustion exercise compared with regular weight training implies
the pre-exhaustion technique may be less effective in
muscle development and strength acquisition.
By using pre-exhaustion exercise the muscle activity, in theory, may increase, as studies have demonstrated that EMG activity consistently increases during
exercise performed at a constant load (6, 7, 14). However, this was not the case in our study, as pre-exhaustion exercise of the knee extensor muscles resulted
in decreased EMG amplitude of the rectus femoris and
vastus lateralis muscles during the leg press exercise.
One possible explanation for this result might be muscle substitution, i.e., that the fatigue of the quadriceps
muscle may have dictated greater use of synergistic
muscle. Although our data showed no significant
change of gluteus maximus muscle activation as a result of pre-exhaustion exercise, it is possible that there
was different activation of other hip extensors, such as
the adductor muscles, or plantar flexion muscles, such
as the gastrocnemius (which also has potential function at the knee) and soleus muscles.
Another method of pre-exhaustion described in the
literature involves fatiguing synergistic or stabilizing
muscles, rather than prime mover agonistic muscles,
before performing the primary exercise movement (2).
An example of this strategy is performing lat pulldowns or military presses prior to performing the
bench press exercise. It is theorized that the fatigued
Figure 2. Mean and SEM of electromyography (EMG)
activity (expressed as percent of maximal voluntary
isometric activation) during a leg press exercise with
compared to without pre-exhaustion exercise for the rectus
femoris, vastus lateralis, and gluteus maximus muscles,
respectively. *Difference (p 5 0.034) from pre-exhausted
condition. **Difference (p 5 0.001) from pre-exhausted
condition.
smaller muscles will contribute less to the movement
of the later exercises, thereby placing greater stress on
the large muscle groups (2). Our data, where the fatigued knee extensor muscles contributed less during
the subsequent leg press exercise, support the idea of
pre-exhausting small synergistic muscles, rather than
prime mover agonistic muscles. Therefore, to meet the
goal of increased quadriceps muscle activity during a
leg press exercise, we speculate that pre-exhaustion ex-
Effect of Pre-Exhaustion Exercise on Muscle Activation
ercise should consist of a hip extension exercise, rather
than a knee extension exercise. Theoretically, this
would force the quadriceps muscles to increased activity because the synergistic hip extensor muscles would
probably contribute less during the leg press exercise.
However, the advantages and disadvantages of different pre-exhaustion exercise combinations in optimizing strength and muscle size need further study.
The vastus lateralis muscle demonstrated higher
EMG activity than that of the rectus femoris muscle
during the leg press exercise both when subjects were
in a non-fatigued and a fatigued state (;75% vs.
;100% of MVIA; Figure 2). We believe that this different EMG amplitude pattern represents the biarticular nature of the rectus femoris muscle, which also
functions at the hip joint. This requires the rectus femoris muscle to decrease its activity since the rectus
femoris muscle is a hip flexor, not a hip extensor.
Subjects performed significantly (p , 0.001) less
repetitions of the leg press exercise when in a pre-exhausted state. This is in accordance with the observations of Fleck and Kraemer (2) who compared the
workout logs of subjects when barbell squats were
placed in the beginning of the workout with those
when squats were placed at the end of the workout.
Significantly heavier resistances were used when
squats were performed first.
Although no training studies have been performed
on the effects of pre-exhaustion exercise, it appears unlikely, based on the acute stresses measured in our
study, that pre-exhaustion exercise would result in
greater gains in muscle strength or hypertrophy than
regular weight training.
Although most weight trainers use a multiple-set
system when performing the pre-exhaustion method,
only 1 set of each exercise was used experimentally in
our study. A multiple-set protocol would not have allowed sufficient recovery from prior pre-exhaustion
and non–pre-exhaustion exercise sets to allow an accurate comparison between conditions.
The movement velocity during the knee extension
exercise was not controlled in our study. This is due
to the fact that the cadence consistently decreases from
the first to the last repetition for a subject during a set
of heavy weight training exercise (11).
When applied to the quadriceps muscle, the preexhaustion technique involves a knee extension exercise combined with either a leg press or a barbell squat
exercise (2). The weight machine leg press exercise was
preferred in our study because of advantages such as
greater control over technique and extraneous body
movement (5), which may have facilitated measurement reliability and objectivity. The free weight barbell squat exercise could be considered more of an
overall body movement, and is in addition probably
more difficult to perform correctly due to greater demands for coordination and balance (5).
415
Empirically, the resistance used when performing
pre-exhaustion exercise is in the 10RM range. With the
intent of reproducing normal training conditions, preexhaustion exercise sets in our study were therefore
performed at a load of 10RM, which approximates
80% of 1RM strength (8, 9). Consequently, quadriceps
muscle force fell to about 80% of maximal strength as
a result of knee extension pre-exhaustion exercise. The
use of different RMs (lighter or heavier resistance than
10RM) when performing pre-exhaustion exercise may
have produced different results.
Practical Applications
Despite the widespread use of pre-exhaustion exercise
by weight trainers as a technique to increase the activation of the targeted (fatigued) muscle during multijoint exercise, pre-exhaustion exercise may have disadvantageous effects on muscle performance, i.e., decreased activation of the fatigued muscle. Also, subjects performed less repetitions of the leg press
exercise when in a pre-exhausted state. Therefore our
data imply that weight trainers using this method
should reconsider its effectiveness in producing
strength and muscle size gains.
Future research in this area should address the effect of a reversed pre-exhaustion strategy, as our data
support the notion of pre-exhausting small synergistic
muscles, rather than prime mover agonistic muscles.
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Med. 31:229–234. 1997.
ROONEY, K., R. HERBERT, AND R. BALNAVE. Fatigue contributes
to the strength training stimulus. Med. Sci. Sports Exerc. 26:
1160–1164. 1994.
SALE, D. Neural adaptation to resistance training. Med. Sci.
Sports Exerc. 20:135–145. 1988.
SCHMIDTBLEICHER, D. Training for power events. In: Strength
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SCHOTT, J., K. MCCULLY, AND O.M. RUTHERFORD. The role of
metabolites in strength training. II. Short versus long isometric
contractions. Eur. J. Appl. Physiol. 71:337–341. 1995.
SISCO, P., AND J. LITTLE. Power Factor Training: A Scientific Approach to Building Lean Muscle Mass. Lincolnwood, IL: Contemporary Books, 1997.
TAN, B. Manipulating resistance training program variables to
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Acknowledgments
This study was supported by a grant from the Swedish
National Centre for Research in Sports.
Address correspondence to Jesper Augustsson, jesper.
[email protected].
Study IV
Single-leg hop testing performed under fatigued
conditions using pre-exhaustion exercise:
reliability and biomechanical analysis
J. Augustsson1,2, R. Thomeé1, C. Lindén3, M. Folkesson4, R. Tranberg1,
J. Karlsson1
1
Department of Orthopaedics, Sahlgrenska University Hospital, Göteborg
University, Göteborg, Sweden, 2Rehabilitation Medicine, Institute of Clinical
Neuroscience, Sahlgrenska University Hospital, Göteborg University, Göteborg,
Sweden, 3Mösseberg Community Health Center, Falköping, Sweden,
4
Department of Physical Therapy, Gävle-Sandviken Hospital, Sweden
Abstract
A pre-exhaustion exercise protocol was combined with single-leg hop testing to improve the
possibilities to evaluate the effects of training or rehabilitation interventions. In the first testretest experiment, 11 healthy male subjects performed two trials of single-leg hops under
three different test conditions: nonfatigued and following pre-exhaustion exercise which
consisted of unilateral weight machine knee extensions at 80% and 50%, respectively, of 1
repetition maximum (1 RM) strength. ICC coefficients ranged from 0.75 to 0.98 for different
hop test conditions, indicating that all tests were highly reliable. For the second experiment,
eight healthy male subjects performed the pre-exhaustion exercise protocol to investigate how
fatigue influences lower-extremity joint kinematics and kinetics during single-leg hops. Hip,
knee and ankle joint angles, moments and powers, as well as ground-reaction forces were
recorded with a six-camera, motion-capture system and a force platform. Recovery of hop
performance following the fatiguing exercise was also measured. During the take-off for the
single-leg hops, hip and knee flexion angles, generated powers for the knee and ankle joints,
and ground-reaction forces decreased for the fatigued hop conditions compared with the
nonfatigued condition (P<0.05). Compared with landing during the nonfatigued condition, hip
moments and ground-reaction forces were lower for the fatigued hop conditions (P<0.05).
Absorbed power was two to three times greater for the knee than for the hip and five to ten
times greater for the knee than for the ankle during landing for all test conditions (P<0.05).
Most measured variables had recovered three minutes post-exercise. It is concluded that the
pre-exhaustion exercise protocol combined with single-leg hop testing was a reliable method
for investigating functional performance under fatigued test conditions. Further, subjects
utilized an adapted hop strategy which employed less hip and knee flexion and generated
powers for the knee and ankle joints during take-off, and less hip joint moments during
landing under fatigued conditions. The large negative power values observed at the knee joint
during the landing phase of the single-leg hop, during which the quadriceps muscle activates
eccentrically, indicate that not only hop distance but also the ability to perform successful
landings should be investigated when assessing dynamic knee function.
Key words: Functional testing, inverse dynamics, jumping
1
Introduction
The ability to perform work or sport activities under fatigued conditions (i.e. the
ability to sustain muscular force and power) is of great importance. Moreover,
injuries often tend to occur at the end of a sporting event, when a participant is
fatigued (Dugan & Frontera, 2000; Feagin, Lambert, Cunningham, Anderson,
Riegel, King, VanGenderen, 1987; Östenberg & Roos, 2000). However, tests of
dynamic function for sports or rehabilitation purposes are generally performed
under nonfatigued test conditions. For example, athletes or patients are generally
not fatigued when performing tests such as single-leg hops or vertical jumps,
and as a consequence, an indication of an individual’s physical-functional
capabilities when in a condition of muscle fatigue is not always provided. To
improve the possibilities to evaluate the effects of training or rehabilitation
interventions, the testing of dynamic function under fatigued conditions has
been suggested (Augustsson & Thomeé, 2000). However, assessing dynamic
performance under fatigued test conditions is problematic; for one thing,
because it requires a standardised method to quantify both the level and the
progression, of fatigue.
Muscle fatigue research has focused primarily on issues such as energy
supply (Sahlin, Tonkonogi, Söderlund, 1998), muscle co-activation (Weir,
Keefe, Eaton, Augustine, Tobin, 1998) and mechanisms underlying the
reduction of force in skeletal muscle fatigue (Westerblad, Allen, Bruton,
Andrade, Lannergren, 1998), whereas the effect of muscle fatigue on functional
performance, such as jumps or hops, has received little attention. The related
issue concerning of whether muscle fatigue might affect postural balance has
been studied with contradictory results (Johnston, Howard, Cawley, Losse,
1998; Adlerton & Moritz, 1996).
Studies of the biomechanical behaviours of the lower-extremity during takeoffs and landings for different jumps and hops have been focused on the
prediction of impact forces (Zhang, Bates, Dufek, 2000), comparisons of landing
techniques (Devita & Skelly, 1992), and optimum take-off techniques (Seyfarth,
Blickhan, van Leeuwen, 2000). Further, the contribution made by muscles
acting across the hip, knee and ankle joints during the propulsive phase of
different hop tests has been estimated (Jacobs, Bobbert, van Ingen Schenau,
1996), and the importance of the quadriceps muscle as a contributor during
jumps for distance has been questioned (Pfeifer & Banzer, 1999; Pincivero,
Lephart, Karunakara, 1997a; Robertson & Fleming, 1987; Östenberg, Roos,
Ekdahl, Roos, 1998). However, we are not aware of any studies investigating the
way fatigue influences the kinetic and kinematic take-off and landing
performances during single-leg hops. Moreover, single-leg hops are used
clinically to assess knee function in patients following knee injury or surgery, as
it is thought that single-leg hops represent an activity which places high
demands on the ability of the leg musculature to generate substantial knee joint
2
moment and power during the take-off (Rudolph, Axe, Snyder-Mackler, 2000).
However, to our knowledge, no published studies have investigated absorbed
power values for the knee during single-leg hop landings; an eccentric loading
situation which we believe is equally demanding on knee function as take-offs.
Further, research evaluating the recovery of functional performance, such as
single-leg hop take-offs and landings, following fatiguing exercise, is limited.
The first aim was to develop, and to examine the reliability of, a single-leg
hop test performed under standardised, fatigued conditions. The second aim was
to obtain biomechanical information concerning the effect of a quadriceps
muscle fatigue protocol on the kinetic and kinematic behaviour of the lowerextremity during single-leg hops. We hypothesised that when subjects were
fatigued they would utilize an adapted hop strategy, and that the contribution
made by the muscles acting across the hip, knee and ankle joints during take-off
would differ depending on the hop test condition. The third aim of our study was
to examine absorbed power values for the hip, knee and ankle joints during
single-leg landings across test conditions. The fourth and final aim of our study
was to investigate the recovery of hop performance following fatiguing exercise
of the quadriceps muscle.
Methods
Subjects
The first experiment, which involved the development of a single-leg hop test
performed under fatigued test conditions, using a test-retest design, included 11
male subjects, healthy and generally physically active with asymptomatic back,
hip and knee function. Their mean (±SD) age, body mass and height were 27±5
years, 75±10 kg and 182±4 cm, respectively.
The second experiment, in which a biomechanical analysis was performed
to investigate how fatigue influences lower-extremity joint kinematics and
kinetics during single-leg hops, included eight male subjects, healthy and
generally physically active with asymptomatic back, hip and knee function.
Their mean (±SD) age, body mass and height were 31±6 years, 80±6 kg and
185±4 cm, respectively. The study was approved by the Human Ethics
Committee at the Faculty of Medicine, Göteborg University, Sweden. Informed
consent was obtained and the rights of subjects were protected.
Pre-test
For both experiments, each subject performed a hop test for familiarisation
purposes and, in addition, a knee-extension 1 repetition maximum (1 RM)
strength determination at a pre-test two to three days before the actual testing
sessions. Functional performance was assessed by a single-leg hop test in which
the subject was instructed to stand on one leg and to position his toes to a mark
on the floor. The subject was then instructed to hop forward as far as possible
3
and to land on the same leg. The subject was allowed to swing his arms freely as
he jumped. The distance, in centimeters, was measured from the toe in the
starting position to the heel where the subject landed. A hop was only regarded
as successful if the subject was able to keep his foot in place while balancing on
one leg (i.e. no extra hops was allowed) until an investigator had marked where
the subject had landed. Failure to do so resulted in a re-hop. The test was
performed until three successful hops were obtained for each leg, with the
starting order of the right or the left leg randomly assigned to the subjects. Each
subject was given two practice trials before the test.
Thereafter, each subject’s unilateral 1 RM strength for the right and the left
leg was determined for a knee-extension exercise by using the maximum weight
that could be lifted for one repetition. Subjects were placed in a variable
resistance knee-extension machine (Model Leg Extension FL 130, Competition
Line, Borås, Sweden). Each subject was instructed by an investigator in the
proper technique for the exercise. The subjects performed two submaximal
warm-up sets of the knee-extension exercise. The starting and ending positions
for the knee-extension exercise were seated with approximately 90° of knee
flexion angle. From the starting position, each subject extended the knee until 0°
of flexion angle and returned to the starting position. The pad supporting the
back was adjusted so that the axis of the knee joint was aligned with the axis of
the resistance arm. The footpad was positioned at approximately five cm
proximal to the lateral malleolus. The weight lifted for each trial was
incremented by 2.5-10 kg until failure occurred. One minute of rest was given
between trials. The starting order of the right or the left leg was randomly
assigned to the subjects.
Experimental protocols
All the subjects in the first experiment participated in two testing sessions to
determine test-retest reliability of hop performance (measured as maximal hop
length) during the different test conditions. Testing took place on two separate
days with at least 72 hours between testing sessions. Hop performance was
compared under three standardised test conditions: nonfatigued and immediately
following fatiguing exercise of the quadriceps muscle at 50% and 80% of 1 RMstrength, respectively.
In order to standardise the fatiguing exercise, we used a fatigue protocol
developed from previous work on healthy subjects (Augustsson, Thomeé,
Hörnstedt, Lindblom, Karlsson, Grimby, 2003). This fatigue protocol consists of
so-called “pre-exhaustion exercise”, which involves working a muscle to fatigue
by performing as many repetitions in a single set as possible at a load of, for
example, 80% of 1 RM, using a single joint exercise, after which that exercise is
followed immediately by a multijoint exercise. By adopting the concept of preexhaustion exercise, and by using the RM continuum, we have constructed a
4
testing protocol that quantifies both the level and the progression, of muscle
fatigue. Specifically, a “target force” of pre-exhaustion activations can be set at
a given percentage of 1 RM-strength (for example, 80% of 1 RM) and in turn
allow for any degree of muscle fatigue to be obtained in a controlled manner.
Thus, if a subject performs as many repetitions as possible until failure with, for
example, 80% of 1 RM, 1 RM-strength consequentially is reduced by 20%.
The pre-exhaustion exercise protocol consisted of performing consecutive
unilateral knee extensions with a load of 50% and 80% of 1 RM, respectively,
until failure occurred using a variable resistance knee-extension machine. Each
subject began the testing by performing single-leg hops for the right and the left
leg under nonfatigued conditions as previously described. Subjects then
performed unilateral fatiguing knee extensions until failure occurred at 80% of 1
RM; the leg tested first was randomized in each subject, followed immediately
by single-leg hops. Finally, the same pre-exhaustion exercise protocol was
repeated at 50% of 1 RM for the contralateral leg. Each subject’s knee flexing
and knee extending cadence was not fixed during the knee-extension exercise.
Instead, each subject was allowed to establish a “groove”, i.e. use a self-selected
cadence. The best hop performance (that is, the hop with maximal hop distance)
for each test conditions was recorded.
The same investigator supervised the tests for all subjects. Verbal
encouragement and instructions were standardised. Before both the pre-test and
testing sessions, each subject performed a warm-up consisting of five minutes of
ergometer cycling at 70 r.p.m. at a submaximal work level, followed by 20
repetitions of bilateral standing toe raises.
For the second experiment, a biomechanical analysis of maximal single-leg
hops during fatigued and nonfatigued conditions was performed using the same
test protocol as for the first experiment. A three-dimensional motion analysis
system (Qualisys Medical AB, Göteborg, Sweden) that consisted of six cameras,
passive reflective markers and a computer running a software package (Qtrac
Capture-Version 2.57, Adaptive Optics Associates, Inc., Cambridge, MA,
U.S.A) was used for the acquisition of kinematic data. Kinetic data were
collected with a Kistler force plate (Kistler 9281C, Kistler Instrumente AG,
Winterthur, Switzerland). Kinematic and kinetic data were recorded at 240 Hz.
The camera system was calibrated to a measurable volume of 13.8 m3 (3 x 2 x
2.3 m). The passive reflective markers were attached directly to the skin (and
shoes) of each subject to minimize errors between the markers and the actual
joint centers, according to the set-up of Fig. 1. The data for the kinematic coordinates, ground-reaction forces, and moments and powers were imported into
customized software to compute joint kinematics, segmental inertia properties,
and joint kinetics using an inverse dynamics model. The variables that were
evaluated included the range of motion, moments and powers of the three lowerextremity joints, together with ground-reaction forces, i.e. horizontal force (Fx),
5
Fig. 1. Marker set-up.
medio-lateral force (Fy), vertical force (Fz) and the resultant vector of vertical
and horizontal forces (Fzx). The joint kinetic values were normalised to the
body mass for each subject. By convention, both the positive and the negative
values for joint movement would represent extensor and flexor moment, and
positive and negative power values would indicate energy generation and
absorption. During take-off, hip, knee and ankle angles values were
documented, when the right anterior spina iliac superior-marker was at its
deepest position. During landing, hip, knee and ankle angles values were
6
collected at peak vertical ground-reaction force. The subjects hopped either from
the force platform or to the force platform for all test conditions. To study
fatigue recovery following the pre-exhaustion exercise protocol, the subjects
again performed single-leg hops after a recovery period of three minutes.
Statistical Methods
For the first experiment, the intraclass correlation (ICC) coefficient was
evaluated for the analysis of test-retest reliability under different hop test
conditions, according to Shrout & Fleiss (1979). The Friedman test was used to
determine differences in hop performance between fatigued and nonfatigued hop
test conditions. Differences between the number of hop trials and knee-extension
repetitions performed at test and retest were computed using the Wilcoxon
signed-rank test. For the second experiment, comparisons between the
biomechanical variables that were obtained were made with the Friedman test.
Significance was considered at the α level of P<0.05.
7
Results
Test-retest reliability for different hop test conditions
For the first experiment, we found high ICC values when analysing test-retest
reliability of hop performance (measured as maximal hop length) during the
different test conditions (Fleiss 1986). ICCs were 0.75, 0.91 and 0.98,
respectively, for the 50% quadriceps strength-hop condition, the 80% quadriceps
strength-hop condition, and the nonfatigued-hop condition. The mean number
(±SD) of hop trials needed to obtain three successful hops at test and retest
under nonfatigued test conditions was 3.5 (range 3-5) and 3.3 (range 3-5), with
no significant differences between tests. The number of hop trials following preexhaustion exercise of the quadriceps muscle at 50% of 1 RM was 4.5 (range 36) and 3.5 (3-5), with a significant (P<0.05) difference between test and retest.
Following pre-exhaustion exercise of the quadriceps muscle at 80% of 1 RM,
the number of hop trials was 3.8 (range 3-6) and 3.3 (range 3-5), with no
significant differences between tests. The average number (±SD) of kneeextension repetitions at 50% of 1 RM was 16.7±2.4 and 17.3±2.7, with no
significant differences between test and retest. The mean number (±SD) of kneeextension repetitions at 80% of 1 RM was 7.1±1.5 and 8.0±1.3, with a
significant (P<0.05) difference between test and retest.
Hop performance under different test conditions
Hop performance decreased significantly, 29 cm (20%) and 16 cm (11%),
respectively, following pre-exhaustion exercise of the quadriceps muscle at 50%
and 80% of 1 RM, compared with the nonfatigued test condition (P<0.01).
Moreover, hop performance decreased significantly, 13 cm (9%), following preexhaustion exercise of the quadriceps muscle at 50% compared with 80% of 1
RM (P<0.01) (Table 1).
Joint range of motion
For the second biomechanical experiment, significant (P<0.05) decreases were
observed for hip and knee flexion angles for the fatigued hop conditions
compared with the nonfatigued hop condition during the ground contact portion
of the take-off (defined as the right anterior spina iliac superior-marker being at
its deepest position) (Table 2 and 3). A graph for hip, knee and ankle joint
angles, moments and powers, as well as ground-reaction forces, during the takeoff for a representative subject is shown in Fig. 2. During landing, hip, knee and
ankle angles values were collected at peak vertical ground-reaction forces. No
significant differences were found during landing between joint flexion angles
for the nonfatigued hop test condition compared with the 50% quadriceps
strength-hop condition (Table 4). Significant (P<0.01) differences were found
during landing between the nonfatigued hop test condition and the 80%
quadriceps strength-hop test condition for hip flexion angles (Table 5).
8
Nonfatigued
Hip
Knee
Ankle
Flexion Angles (°)
80
60
40
20
0
-20
0
0,2
0,4
0,6
0,8
1
100
60
40
20
0
1,2
-20
4
0,4
0,6
0,8
1
1,2
1
0
0
0,2
0,4
0,6
0,8
1
Hip
Knee
Ankle
3
Moment (Nm)
Moment (Nm)
2
1,2
2
1
0
-1
-2
0
0,2
0,4
0,6
0,8
1
1,2
-2
-3
-3
25
25
Hip
Knee
Ankle
15
10
5
0
v
-5 0
0,2
0,4
0,6
0,8
1
1,2
15
10
5
0
-5 0
-10
-10
-15
-15
-20
-20
-25
-25
2000
2000
Fx
Fy
Fz
1500
Hip
Knee
Ankle
20
Power (W)
20
Power (W)
0,2
4
Hip
Knee
Ankle
3
0,2
0,4
0,6
0,8
1
1,2
Fx
Fy
Fz
1500
1000
Force (N)
1000
Force (N)
0
-40
-40
-1
Hip
Knee
Ankle
80
Flexion Angles (°)
100
Fatigued
500
500
0
0
0
0,2
0,4
0,6
-500
0,8
1
0
1,2
0,2
0,4
0,6
0,8
1
1,2
-500
-1000
-1000
Time (sec)
Time (sec)
Fig. 2. Representative hip, knee and ankle joint angles, moments and powers,
as well as ground-reaction forces during the take-off for a single subject for
nonfatigued and fatigued (50% of quadriceps muscle 1 RM-strength) hop
conditions. The vertical dotted lines indicate the time of take-off when the subject
becomes airborne.
9
Kinetics
As seen in Table 2, during the take-off for the single-leg hops, moments for the
knee and ankle joints, and generated powers for the hip, knee and ankle joints
decreased for the 50% quadriceps strength-hop condition compared with the
nonfatigued hop condition (P<0.05). Significant differences for hip joint
moment and knee and ankle joint powers were found between the nonfatigued
hop test condition and the 80% quadriceps strength-hop test condition (P<0.05)
(Table 3). The hip, knee and ankle joint powers generated during the take-off
differed significantly for different hop conditions (P<0.05). The percentage
contributions at the hip, knee and ankle joints to the total generated powers
generated by all three joints for different hop conditions were 28% to 36% (7.0
to 10.4 W/kg body mass), 20% to 31% (3.9 to 11.6 W/kg body mass) and 41%
to 44% (8.5 to 15.0 W/kg body mass), respectively (Fig. 3). Compared with
landing during the nonfatigued condition, hip moment and absorbed knee power
were lower for the 50% quadriceps strength-hop condition (P<0.05) (Table 4),
whereas hip moment decreased for the 80% quadriceps strength-hop condition
(P<0.01) (Table 5). The mean absorbed power values were typically two to
three times higher for the knee than for the hip and five to ten times higher for
the knee than for the ankle during landing for all test conditions (P<0.01) (Fig.
4).
***
16,0
*
*
**
**
14,0
12,0
Power (W)
10,0
8,0
6,0
4,0
2,0
0,0
Hip joint
Knee joint
Ankle joint
Nonfatigued
80% strength
50% strength
Fig. 3. Comparison of generated power values during the take-off for the hip,
knee and ankle joint for different hop test conditions. Values are expressed as
means (±SD). *P<0.05. **P<0.01. ***P<0.001.
10
0,0
Hip joint
Knee joint
Ankle joint
-5,0
Power (W)
-10,0
-15,0
-20,0
-25,0
-30,0
-35,0
***
***
***
**
**
**
**
Nonfatigued
80% strength
50% strength
Fig. 4. Comparison of absorbed power values during landings for the hip, knee
and ankle joint for different hop test conditions. Values are expressed as means
(±SD). **P<0.01. ***P<0.001.
Ground-reaction forces
During the take-off for the single-leg hops, the horizontal forces decreased for
the 50% quadriceps strength-hop condition compared with the nonfatigued hop
condition (Table 2), whereas the vertical and horizontal forces, as well as the
resultant vector of vertical and horizontal forces, decreased for the 80%
quadriceps strength-hop condition (Table 3) (P<0.05). Compared with landing
during the nonfatigued condition, the vertical and horizontal forces, as well as
the resultant vector of vertical and horizontal forces, decreased following preexhaustion of the quadriceps muscle at 50% of 1 RM-strength (Table 4),
whereas the vertical forces and the resultant vector of vertical and horizontal
forces decreased following pre-exhaustion of the quadriceps muscle at 80% of 1
RM-strength (Table 5) (P<0.05). There was no significant difference in mediolateral force between hop test conditions at take-off or during landing (Tables 25).
11
Recovery
Almost all the measured variables had fully recovered three minutes postexercise for the fatigued hop conditions (i.e. following pre-exhaustion of the
quadriceps muscle at 80% and 50% of 1 RM-strength) during take-offs and
landings (Tables 2-5). However, after three minutes of recovery there was a
decrease in knee flexion angles at the take-off for the 80% quadriceps strengthhop condition (P<0.05) (Table 3). Moreover, the horizontal force at landing was
significantly lower for the 50% quadriceps strength-hop condition protocol
following recovery (P<0.05) (Table 4).
Table 1. Hop performance for test and retest under different test conditions
in healthy male subjects (n=11). Values are expressed as means (±SD).
Quadriceps muscle 1 RM-strength (%)
Nonfatigued
80
50
Hop performance (cm)
Test
169.4±20.4**¤
152.6±20.2*
Retest
168.8±20.2**¤¤ 153.0±20.4**
139.5±12.2
141.3±22.5
¤ Different from 80% quadriceps strength-hop condition, P<0.01.
¤¤ Different from 80% quadriceps strength-hop condition, P<0.001.
* Different from 50% quadriceps strength-hop condition, P<0.01.
** Different from 50% quadriceps strength-hop condition, P<0.001.
12
Table 2. Hip, knee and ankle joint angles, moments and powers and ground-reaction forces during
the take-off for the nonfatigued hop test condition, the 50% quadriceps strength-hop test condition
and the recovered hop test condition, respectively. Values are expressed as means (±SD).
Nonfatigued
50% strength
Recovery (3 min)
Flexion Angles ( °)
Hip
Knee
Ankle
79.79 ± 7.96**
66.56 ± 8.55**
31.11 ± 4.75
58.26 ± 7.28
54.78 ± 5.98
27.44 ± 3.40
77.47 ± 5.64**
61.34 ± 9.21**
30.84 ± 3.90
Moment (Nm/kg)
Hip
Knee
Ankle
4.11 ± 1.58
2.25 ± 0.98**
2.44 ± 0.18**
2.95 ± 0.42
1.49 ± 0.44
2.22 ± 0.20
3.44 ± 0.68
1.95 ± 0.70**
2.55 ± 0.17**
Generated Power (W/kg)
Hip
Knee
Ankle
10.29 ± 2.89*
10.24 ± 4.67**
14.58 ± 2.23**
7.04 ± 0.74
3.93 ± 0.85
8.53 ± 1.49
10.47 ± 3.23
7.84 ± 3.17**
13.28 ± 1.86**
Force (N)
Fx
Fy
Fz
Fzx
587.54 ± 110.22**
60.36 ± 15.09
1441.60 ± 172.81
1557.53 ± 197.21
373.36 ± 72.77
65.66 ± 22.33
1355.61 ± 170.49
1407.44 ± 172.02
543.68 ± 90.64**
57.93 ± 16.55
1470.85 ± 211.96*
1568.49 ± 227.31
*Difference (P <0.05) from 50% quadriceps strength-hop condition.
**Difference (P <0.01) from 50% quadriceps strength-hop condition.
Table 3. Hip, knee and ankle joint angles, moments and powers and ground-reaction forces during
the take-off for the nonfatigued hop test condition, the 80% quadriceps strength-hop test condition
and the recovered hop test condition, respectively. Values are expressed as means (±SD).
Nonfatigued
80% strength
Recovery (3 min)
Flexion Angles ( °)
Hip
Knee
Ankle
78.64 ± 12.32*
63.55 ± 5.53**¤
27.42 ± 4.68
66.18 ± 13.58
56.79 ± 7.02
27.66 ± 2.84
69.81 ± 20.52
57.88 ± 9.04
28.60 ± 6.30
Moment (Nm/kg)
Hip
Knee
Ankle
4.31 ± 1.32*
2.43 ± 0.87
2.51 ± 0.25
3.39 ± 0.59
1.76 ± 0.56
2.48 ± 0.20
3.60 ± 0.79
1.94 ± 0.37
2.66 ± 0.36*
Generated Power (W/kg)
Hip
Knee
Ankle
10.39 ± 1.02
11.58 ± 4.00*
15.03 ± 2.15**
8.93 ± 2.20
6.19 ± 2.54
11.80 ± 2.61
10.15 ± 2.44
8.57 ± 2.92
15.44 ± 3.88**
Force (N)
Fx
Fy
Fz
Fzx
579.08 ± 117.40**
72.74 ± 15.29
1555.93 ± 238.50*
1661.84 ± 252.69**
419.55 ± 63.65
65.67 ± 19.83
1411.94 ± 231.69
1473.65 ± 235.12
525.07 ± 57.91**
70.83 ± 23.42
1542.54 ± 198.12
1629.68 ± 204.18**
*Difference (P <0.05) from 80% quadriceps strength-hop condition.
**Difference (P <0.01) from 80% quadriceps strength-hop condition.
¤Difference (P <0.01) from recovered-hop condition.
13
Table 4. Hip, knee and ankle joint angles, moments and powers and ground-reaction forces during
landing for the nonfatigued hop test condition, the 50% quadriceps strength-hop test condition
and the recovered hop test condition, respectively. Values are expressed as means (±SD).
Nonfatigued
50% strength
Recovery (3 min)
Flexion Angles ( °)
Hip
Knee
Ankle
61.67 ± 6.38
21.97 ± 5.35
-1.90 ± 6.29
51.51 ± 11.60
19.44 ± 6.44
-4.54 ± 3.05
60.74 ± 6.02
21.87 ± 3.71
-7.49 ± 6.87
Moment (Nm/kg)
Hip
Knee
Ankle
14.44 ± 4.13*
-3.00 ± 4.82
1.02 ± 2.11
6.27 ± 2.71
-1.61 ± 0.82
-0.42 ± 0.27
11.67 ± 3.02
-3.18 ± 3.81
0.88 ± 2.06
Absorbed Power (W/kg)
Hip
Knee
Ankle
-11.13 ± 3.54
-29.79 ± 5.09**
-2.43 ± 3.97
-10.66 ± 5.12
-18.80 ± 2.99
-4.06 ± 0.58
-11.22 ± 6.63
-25.98 ± 5.60**
-4.49 ± 2.14
Force (N)
Fx
Fy
Fz
Fzx
-1679.88 ± 318.86*¤
-250.78 ± 202.46
3729.10 ± 882.09**
4095.32 ± 908.10**
-1048.47 ± 302.71
-174.49 ± 45.60
2491.83 ± 418.55
2709.25 ± 476.92
-1339.91 ± 219.10*
-262.75 ± 131.33
3371.24 ± 550.88**
3643.46 ± 456.99**
¤Difference (P <0.05) from recovered hop condition.
*Difference (P <0.05) from 50% quadriceps strength-hop condition.
**Difference (P <0.01) from 50% quadriceps strength-hop condition.
Table 5. Hip, knee and ankle joint angles, moments and powers and ground-reaction forces during
landing for the nonfatigued hop test condition, the 80% quadriceps strength-hop test condition
and the recovered hop test condition, respectively. Values are expressed as means (±SD).
Nonfatigued
80% strength
Recovery (3 min)
Flexion Angles ( °)
Hip
Knee
Ankle
58.19 ± 12.18**
21.61 ± 2.40
-5.54 ± 7.78
48.30 ± 5.84
17.18 ± 3.77
-4.44 ± 4.74
58.55 ± 10.40**
18.73 ± 7.27
-5.10 ± 6.35
Moment (Nm/kg)
Hip
Knee
Ankle
13.47 ± 5.65**
-2.86 ± 5.01
-0.14 ± 1.12
7.75 ± 2.84
-2.37 ± 1.06
-0.02 ± 0.82
12.96 ± 7.83**
-3.10 ± 6.23
-0.51 ± 1.13
Absorbed Power (W/kg)
Hip
Knee
Ankle
-9.52 ± 1.75
-31.11 ± 7.88
-4.79 ± 4.35
-10.07 ± 6.34
-22.97 ± 7.53
-5.46 ± 1.48
-8.75 ± 3.86
-22.12 ± 4.14
-4.91 ± 3.73
Force (N)
Fx
Fy
Fz
Fzx
-1628.42 ± 420.48
-171.31 ± 359.16
3260.52 ± 729.12*
3651.02 ± 805.81**
-1238.85 ± 226.34
-237.42 ± 115.03
2777.54 ± 509.15
3046.68 ± 520.68
-1751.56 ± 439.10*
-272.89 ± 124.96
3438.57 ± 779.30
3861.49 ± 880.88**
*Difference (P <0.05) from 80% quadriceps strength-hop condition.
**Difference (P <0.01) from 80% quadriceps strength-hop condition.
14
Discussion
The aim of our study was firstly to develop, and to examine the reliability of, a
single-leg hop test performed under standardised, fatigued conditions using preexhaustion exercise, and secondly, to obtain biomechanical information about
the effect of quadriceps muscle fatigue on the kinetic and kinematic behaviour
of the lower-extremity during single-leg hops. For the first experiment, the testretest reliability of different hop test conditions was determined. Hop
performance under all three test conditions was found to have high test-retest
reliability. We have thus developed a reliable method that is easy to perform and
record and which, in the clinical setting, can be used to compare functional
performance under different, standardised test conditions. For the second
biomechanical experiment, the main findings were that hip and knee flexion
angles, knee and ankle joint power, and ground-reaction forces decreased for the
fatigued hop conditions compared with the nonfatigued condition during the
take-off for the single-leg hops. Compared with landing during the nonfatigued
condition, hip moments and ground-reaction forces were lower for the fatigued
hop conditions. The absorbed power values were two to three times greater for
the knee than for the hip and five to ten times greater for the knee than for the
ankle during landing for all test conditions. Most measured variables had
recovered three minutes post-exercise.
Two aspects of the test-retest results deserve mentioning; firstly, the fact
that the test-retest reliability decreased as fatigue of the quadriceps muscle
increased (from 0.98 to 0.75) indicates that a pre-exhaustion exercise protocol
generating more than 50% muscle fatigue may lead to poorer reproducibility. It
is not unexpected that reproducibility decreases when the level of muscle fatigue
increases. For example, Johnston et al. (1998) found significant decreases in
motor control performance following lower-extremity exercise to fatigue. Our
results at 50% quadriceps muscle strength are in agreement with those reported
by Pincivero, Lephart, Karunakara (1997b), who obtained test-retest ICC values
ranging from 0.52 to 0.74 for a muscular endurance test of 30 maximal
repetitions of isokinetic knee extension/flexion at 180°/s. Moreover, Manske,
Smith, Wyatt (2003) recently investigated whether multijoint isokinetic testing
before functional testing altered test-retest reliability of several functional tests
(including the single-leg hop) of the lower-extremity. It was found that testretest reliability was high for all functional tests, with ICCs ranging from 0.91 to
0.98 (ICC value for the single-leg hop test was 0.96). Secondly, in our study, the
average number of knee-extension repetitions differed significantly (P<0.05)
between test (7.1 repetitions) and retest (8.0 repetitions) at 80% of 1 RM. This
difference may be the result of a learning process, as well as feedback in the
form of knowledge of results from the previous test session. However, although
there was a difference in the number of knee-extension repetitions performed by
subjects at 80% of 1 RM, the hop test-retest reliability was high (ICC value
15
0.91) for this test condition.
The fatigue induced by our pre-exhaustion exercise protocol was probably
the result of peripheral fatigue, i.e. changes within the quadriceps muscle itself,
rather than a failure of central drive. This is supported by James, Sacco, Jones
(1995), who demonstrated a minimal reduction in central drive during heavy
exercise, resulting in a 50% loss of power. Furthermore, Beelen, Sargeant,
Jones, de Ruiter (1995) noted a close association between the changes in
electrically elicited force and voluntary force following high-intensity dynamic
exercise. The authors (Beelen et al., 1995) suggest that fatigue may be due to
changes in the contractile apparatus and is probably not a result of reduced
muscle activation by the central nervous system. Peripheral fatigue can be
further divided into high- and low-frequency fatigue (Edwards, Hill, Jones,
Merton, 1977). High-frequency fatigue occurs as a result of an impairment in
action potential propagation over the sarcolemma; low-frequency fatigue
denotes an impairment in excitation-contraction coupling. During high intensity
exercise of short duration, as in our study, high frequency fatigue has been
suggested as the dominant reason for the loss of force-generating capability
(Strojnik & Komi, 1998).
The movement velocity during the exhaustive knee-extension exercise set
was not controlled in our study. This is due to the fact that the cadence
consistently decreases from the first to the last repetition for a subject during a
set of heavy weight training exercise (Jones, Hunter, Fleisig, Escamilla, Lemak,
1999).
When it came to the biomechanical experiment, the hip and knee joints
responded with a reduction in flexion angles during the take-off for the fatigued
conditions, i.e. subjects used a more erect body position. This probably resulted
in the subjects being less capable of generating horizontal forces for the fatigued
conditions. During landing, no significant changes in joint flexion angles were
seen, except for the hip joint, which was more extended for the 80% quadriceps
strength condition. Similarly, Decker, Torry, Noonan, Riviere, Sterett (2002),
who investigated landing performance during a 60-cm vertical drop landing by
subjects with anterior cruciate ligament (ACL) reconstruction, reported a greater
hip extension at initial ground contact compared with healthy subjects. Thus, an
extension of the hip seems to be an adaptation made by subjects with knee
injury, or during conditions of quadriceps fatigue in healthy subjects, during
high-demand landings.
During the take-off for the single-leg hops, moments and generated powers
for the hip, knee and ankle joints decreased for the fatigued conditions. The
decrease in joint moment during fatigued hop conditions ranged from 9% to
44%, whereas the reduction in power ranged from 16% to 62%, indicating that
when fatigued, subjects were typically less capable of generating power than
moment. This is in accordance with the observation by Alkjaer, Simonsen,
16
Magnusson, Aagaard, Dyhre-Poulsen (2002), that power of the knee extensors
during a forward lunge was significantly lower in ACL deficient subjects than in
healthy controls. Presumably, the difference in power for the ACL deficient
subjects was primarily due to a slower angular velocity in the flexion part and to
both reduced moment and slower angular velocity during the extension part.
Our findings showed that the quadriceps muscle contributed significantly
for the propulsive phase of single-leg hops (Fig. 3). In contrast, Robertson &
Fleming (1987) estimated that the contributions by the hip, knee and ankle
extensor muscles were as follows: 46%, 4%, and 50%, respectively, during
standing broad (horizontal) jumping. The results of our study, however,
demonstrate that strong quadriceps muscles are necessary for optimal hop for
distance performance.
Single-leg hop tests are often used as predictors of dynamic knee joint
function, particularly in subjects with ACL injury (Fitzgerald, Lephart, Hwang,
Wainner, 2001). For example, a ratio of limb symmetry known as the limb
symmetry index (LSI) has been the most frequently reported criterion for
assessing whether a hop test is normal or abnormal (Ageberg, 2002). The LSI is
used to calculate the difference in hop length — i.e. the ability to generate power
at the take-off — between the injured and uninjured sides. To our knowledge,
however, no previous studies have investigated the magnitude of eccentric
loading on the knee joint during single-leg hop landings; a situation which could
be considered highly demanding on knee function. We noted that absorbed
power values were two to three times greater for the knee than for the hip, and
five to ten times greater for the knee than for the ankle during landing for all test
conditions (Fig. 4). Based on our results, it is possible that, during single-leg
hop tests, for clinical or scientific purposes, the focus of interest should shift
from the ability to generate power during the take-off to the ability to absorb
power during landing. Thus, we suggest that in order to obtain a more
comprehensive assessment of knee function (e.g. after ACL injury), attention
should not centre exclusively on comparisons between the hop distance on the
injured and uninjured sides, but also on the ability to successfully perform
landings.
During the take-off for the single-leg hops, the horizontal ground-reaction
forces decreased significantly for the fatigued conditions. As mentioned earlier,
this is probably due to the fact that the hip and knee joints responded with a
decrease in flexion angles during the take-off for the fatigued conditions, i.e.
subjects used a more erect body position. Moreover, the single-leg hop distance
decreased significantly as a result of quadriceps muscle fatigue (Table 1). For
this reason, the vertical and horizontal ground-reaction forces during landing
were probably lower for the fatigued conditions because a reduction in hop
length also results in a decrease of impact forces. This is in accordance with
Zhang et al. (2000), who investigated changes in lower-extremity energy
17
absorption for drop jumps of different heights. It was demonstrated, that with
increases in jump height, there were increases in ground-reaction forces.
Most measured variables had fully recovered three minutes post-exercise for
the fatigued hop conditions during both take-off and landing. Schwender,
Mikesky, Wigglesworth, Burr (1995) evaluated subjects for fatigue and recovery
following fatiguing isokinetic exercise of the quadriceps muscle. It was found
that recovery varied among subjects, but was directly related to the decline in
force output. In our study, there was a difference in the decline in force output
for the two fatigue protocols, as quadriceps muscle performance fell to 50% and
80% of 1 RM-strength, respectively. However, recovery of the measured
variables of hop performance following the different fatigue protocols was
similar three minutes post-exercise.
Perspective
Although injuries tend to occur more frequently at the end of a sporting event,
when a participant is fatigued (Dugan & Frontera 2000; Feagin et al. 1987;
Östenberg & Roos 2000), tests of functional performance for sports or
rehabilitation purposes are typically performed under nonfatigued test
conditions. Therefore, our pre-exhaustion exercise protocol combined with
single-leg hop testing may improve the possibilities to evaluate the effects of
training or rehabilitation interventions, as it affords examination of lowerextremity muscle function under conditions of fatigue. The large negative power
values observed at the knee joint during the landing phase of the single-leg hop,
during which the quadriceps muscle activates eccentrically, indicate that not
only hop distance but also the ability to perform successful landings should be
investigated when assessing dynamic knee function. However, more research is
needed and a challenge for future research should be to compare the dynamic
performance of the healthy and injured leg under different test conditions during
rehabilitation and follow-up in patients with ACL injury or reconstruction, for a
more comprehensive assessment of lower-extremity function.
Acknowledgements
This study was supported by a grant from the Swedish National Centre for
Research in Sports.
18
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20
Study V
Knee Surg Sports Traumatol Arthrosc
(2004) 12 : 350–356
KNEE
DOI 10.1007/s00167-004-0518-4
Jesper Augustsson
Roland Thomeé
Jon Karlsson
Received: 21 August 2003
Accepted: 19 February 2004
Published online: 8 May 2004
© Springer-Verlag 2004
J. Augustsson (✉) · R. Thomeé ·
J. Karlsson
Lundberg Laboratory
for Human Muscle Function
and Movement Analysis,
Department of Orthopaedics,
Sahlgrenska University Hospital,
Göteborg University,
413 45 Göteborg, Sweden
Tel.: +46-31-426891,
Fax: +46-31-416816,
e-mail: [email protected]
J. Augustsson
Department of Rehabilitation Medicine,
Sahlgrenska University Hospital,
Göteborg University, Göteborg, Sweden
Ability of a new hop test
to determine functional deficits
after anterior cruciate
ligament reconstruction
Abstract The aim of this study was
to investigate the ability of a new hop
test to determine functional deficits
after anterior cruciate ligament (ACL)
reconstruction. The test consists of
a pre-exhaustion exercise protocol
combined with a single-leg hop.
Nineteen male patients with ACL reconstruction (mean time after operation 11 months) who exhibited normal single-leg hop symmetry values
(≥90% compared with the non-involved extremity) were tested for
one-repetition maximum (1 RM)
strength of a knee-extension exercise. The patients then performed
single-leg hops following a standardised pre-exhaustion exercise protocol, which consisted of unilateral
weight machine knee-extensions until failure at 50% of 1 RM. Although
no patients displayed abnormal hop
symmetry when non-fatigued, 68%
of the patients showed abnormal hop
symmetry for the fatigued test condi-
Introduction
Injuries often tend to occur at the end of a sporting event,
when a participant is fatigued [10, 12, 35]. However, it
has been our observation that current functional tests,
such as the single-leg hop, are typically performed under
non-fatigued test conditions both in the clinical and scientific setting. The ability of these tests to assess whether a
patient has regained lower-extremity function after anterior cruciate ligament (ACL) reconstruction, for example,
could therefore be regarded as limited. In accordance with
this, the reported sensitivity of several types of hop tests
tion. Sixty-three per cent exhibited
1 RM strength scores of below 90%
of the non-involved leg. Eighty-four
percent of the patients exhibited abnormal symmetry in at least one of
the tests. Our findings indicate that
patients are not fully rehabilitated
11 months after ACL reconstruction.
It is concluded that the pre-exhaustion exercise protocol, combined
with the single-leg hop test, improved testing sensitivity when evaluating lower-extremity function after
ACL reconstruction. For a more
comprehensive evaluation of lowerextremity function after ACL reconstruction, it is therefore suggested
that functional testing should be performed both under non-fatigued and
fatigued test conditions.
Keywords Anterior cruciate
ligament · Knee · Rehabilitation ·
Muscle fatigue · Exercise test
in detecting functional limitations in ACL-deficient knees
was relatively low [23, 29]. To improve the sensitivity of
tests of lower-extremity function in evaluating the effect
of rehabilitation interventions, the testing of dynamic
function under fatigued conditions has been suggested
[6]. We have previously developed, and examined the reliability of a single-leg hop test performed under standardised, fatigued conditions in healthy subjects. The results
of this work showed high test-retest reliability for the
fatigued hop-test condition (J. Augustsson et al., submitted). We hypothesised that performing single-leg hop testing under conditions of fatigue may be more sensitive in
detecting functional impairment after ACL reconstruc-
351
tion, when compared with traditional, non-fatigued hop
testing.
The purpose of this study was to investigate the ability
of a new hop test to determine functional deficits after
ACL reconstruction.
Materials and methods
Patients
Nineteen male patients with a unilateral ACL injury who
had undergone ACL reconstruction were recruited for this
study in a consecutive manner from a cohort of patients
that had undergone reconstruction of the ACL at Sahlgrenska University Hospital, Östra, Sweden. The inclusion criteria included there being no other or subsequent
injuries to the surgical limb, and no injury to the uninvolved knee, hips, ankles or back. Further inclusion criteria were at least six months of post-operative physical
therapy, a single-leg hop symmetry index of ≥90%, age
between 20 and 35 years, male gender and pain intensity
of less than five on a 10–cm visual analogue scale (VAS)
on the day of the examination. Clinical knee-joint examination, performed on both of the patients’ knees by an experienced physical therapist (R.T.), revealed no signs of
increased laxity (using the Lachman test), swelling, joint
line tenderness or decreased range of motion.
The descriptive data of the patients was mean (±SD)
age, body weight and height of 28±5 years, 79±8 kg and
182±5 cm respectively. Mean (±SD) time since surgery
was 11±2 months, whereas the mean time (±SD) between
the index injury and reconstruction was 22±17 months. All
the patients were at least recreational athletes and 69%
(13/19) had returned to their previous level of sports participation. In 16 cases, the ruptured ACL was reconstructed
with a patellar tendon autograft, whereas a hamstring-tendon autograft was used in three cases. In ten cases, the
right leg was the injured leg, whilst in nine cases the left
leg was the injured leg. Eleven patients had an isolated
rupture of the ACL, seven patients had ruptures of the lateral meniscus and one patient had a rupture of the medial
meniscus. The study was approved by the Human Ethics
Committee at the Faculty of Medicine, Göteborg University, Sweden. Informed written consent was obtained and
the rights of patients were protected.
Research design
Each patient performed three testing sessions, with at least
7 days between sessions. At the first session, a hop test
under non-fatigued conditions was performed for familiarisation purposes and in addition knee-extension onerepetition maximum (1 RM) strength was determined. At
the second session, knee-extension 1 RM strength was de-
termined again in a test-retest design. The hop test was
then performed under fatigued conditions (see below for
test procedure) for familiarisation purposes. At the third
session, patients performed the hop test under non-fatigued and fatigued test conditions.
All the strength and functional tests were conducted in
a blinded fashion, as patients concealed their knees by
wearing elastic wraps. In this way, the test leader (J.A.)
did not know whether the involved or the non-involved
leg was being tested during a particular test session.
Pre-test procedures
When performing the single-leg hop test, the patient was
instructed to stand on one leg and to position his toes to a
mark on the floor. The patient was then instructed to hop
forward as far as possible and to land on the same leg. The
patient was instructed to hold his hands on his hips
throughout the jump. The distance, in centimetres, was
measured from the toe in the starting position to the heel
where the patient landed. A hop was only regarded as successful if the patient was able to keep his foot in place after landing (i.e., no extra hops for balance correction were
allowed) until the investigator had marked where the patient landed. The test was performed until three successful
hops were made with each leg, with the starting order of
the right or the left leg randomly assigned to the patients.
For the non-fatigued condition, each patient was given
two practice trials before the test.
Each patient’s unilateral 1 RM for the involved and the
uninvolved leg was determined for a knee-extension exercise by using the maximum weight that could be lifted for
one repetition. Patients were placed in a variable-resistance knee-extension machine (Model Leg Extension FL
130, Competition Line, Borås, Sweden). Each patient was
instructed in the proper technique for the exercise by the
test leader. The patients performed two sub-maximal
warm-up sets of the knee-extension exercise. The starting
and ending positions for the knee-extension exercise were
seated with a knee flexion angle of approximately 90°.
From the starting position, each patient extended his knee
and returned to the starting position. The pad supporting
the back was adjusted so that the axis of the knee joint
was aligned with the axis of the resistance arm. The footpad was positioned approximately 5 cm proximal to the
lateral malleolus. The weight lifted for each trial was incremented by 2.5–10 kg until failure occurred. One minute
of rest was allowed between trials. The starting order of
the right or the left leg was randomly assigned to patients.
A strength [26] and hop [19] symmetry index of ≥90%
(involved versus non-involved side) was considered to be
within normal ranges.
352
1 RM, for example, quadriceps 1 RM strength is consequently reduced by 50%.
Each patient began testing by performing single-leg
hops for the involved and uninvolved limb under nonfatigued conditions, as previously described. The patients
then performed unilateral fatiguing knee-extensions until
failure occurred at 50% of their respective 1 RM, using a
variable-resistance knee-extension machine, followed immediately by single-leg hops. The leg tested first was randomised in each patient.
Each patient’s knee-flexing and knee-extending cadence
was not fixed during the knee-extension exercise; instead,
each patient was allowed to establish a “groove”, i.e. use
a self-selected cadence. The best hop performance for the
two test conditions was recorded. The number of hop trials needed to make three successful hops for the different
test conditions was documented, as well as the number of
knee-extension repetitions performed at 50% of 1 RM.
Verbal encouragement and instructions were standardised. Before both the pre-test and the testing sessions,
each patient performed a warm-up consisting of 10 min of
ergometer cycling at 70 rpm at a sub-maximal work level,
followed by 15 squats and 20 repetitions of toe raises. All
the patients wore the same type of athletic shoes during all
the sessions.
Fig. 1 Testing set-up: the patients performed unilateral pre-exhaustion exercise of the quadriceps muscle until failure using a
variable-resistance knee-extension machine at a load of 50% of
1 RM, followed by a single-leg hop
Experimental protocol
The hop performance was compared in two standardised
test conditions: (1) non-fatigued, and (2) immediately following pre-exhaustion exercise of the quadriceps muscle
at 50% of 1 RM strength (Fig. 1). In order to standardise
the fatiguing exercise, we used a fatigue protocol developed from previous work on healthy subjects [5], (J. Augustsson et al., submitted). This fatigue protocol consists
of a so-called “pre-exhaustion exercise”, which involves
working a muscle to fatigue by performing as many repetitions as possible in a single set at a load of, for example,
50% of 1 RM, using a single-joint exercise; this exercise
is immediately followed by a multijoint exercise. By adopting the concept of pre-exhaustion exercise, and by using
the RM continuum, we have constructed a testing protocol that quantifies both the level and the progression of
muscle fatigue.
Specifically, a “target force” of pre-exhaustion activations can be set at a given percentage of 1 RM strength
(for example, 50% of 1 RM) and in turn allow for any degree of muscle fatigue to be obtained in a controlled manner. So, if a subject performs as many repetitions as possible of a knee-extension exercise until failure at 50% of
Power analysis
Based on a hypothesised 5–10% difference in performance between hop-test conditions using the involved
and non-involved leg, the number of patients required to
achieve a power of 0.90 was estimated by power analysis.
Statistical methods
The intraclass correlation (ICC) coefficient was computed
for analyses of the test-retest reliability of the 1 RM test,
according to Shrout and Fleiss [27]. Differences in performance between fatigued and non-fatigued hop-test conditions for the involved and the non-involved side, and differences between the number of hop trials and knee-extension repetitions, were analysed using paired t-tests.
The significance was considered at the α level of p<0.05.
Results
Hop and strength-testing symmetry
Because normal hop symmetry was required to be included in this study, all the patients had hop-index values
above or equal to 90% for the hop test performed under
non-fatigued conditions. However, 68% of the patients
(13/19) demonstrated abnormal hop symmetry under fa-
353
exhaustion exercise of the quadriceps muscle at 50% of
1 RM for the involved and the non-involved side was 5.0
(range 3–9) and 4.4 (range 3–7) respectively, with no significant difference between sides (p=0.08).
No patients included in the study experienced pain according to the VAS at the day of the examination.
Test–retest reliability for the 1-RM test
When analysing test-retest reliability for the 1-RM kneeextension test we found excellent ICC [27] values – 0.96 –
for both the involved and the non-involved leg.
Discussion
Fig. 2 Results of the tests of functional ability and 1 RM kneeextension strength. Values shown are percentages of patients after
ACL reconstruction within the normal range [19, 26]
tigued conditions (following pre-exhaustion of the quadriceps at 50% of 1 RM) when testing their ACL-reconstructed
leg. The percentage of patients with abnormal 1 RM kneeextension strength scores was 63% (12/19). Eighty-four
percent of the patients (16/19) exhibited abnormal symmetry in at least one of the tests (Fig. 2).
A summary of the results of the hop and strength tests
is shown in Table 1. “Sensitivity” expresses the percentage of patients with ACL reconstruction who showed abnormal lower-limb symmetry values in the tests. Taken together, the sensitivity level was 0% for the non-fatigued
hop test, 68% for the hop test performed under fatigued
conditions, 63% for the 1 RM strength test, and 84% if we
defined the patients as abnormal when at least one of the
three tests showed an abnormal value.
The mean number (±SD) of repetitions of knee-extensions until failure at 50% of 1 RM was not significantly
different for the involved and the non-involved leg (22±
4 repetitions vs 21±3 repetitions, p=0.49). The mean number of hop trials needed to obtain three successful hops for
the involved and the non-involved side under non-fatigued test conditions was 5.0 (range 3–7) and 5.7 (range
3–8) respectively, with no significant difference between
sides (p=0.08). The number of hop trials following pre-
In addition to the single-leg hop test, which is the most
commonly used test in current practice to assess knee function following ACL reconstruction [14, 25], we developed
a new test in which hop performance was investigated during conditions of fatigue. We hypothesised that this
method would improve the possibility to evaluate the effects of rehabilitation interventions. We found that patients
with normal single-leg hop ability achieved poorer results
using the involved leg when performing single-leg hops in
a fatigued state. The functional disability after ACL reconstruction could therefore be better delineated by the combination of pre-exhaustion exercise followed by a singleleg hop test, rather than by a single-leg hop test alone. The
higher sensitivity of the combined pre-exhaustion exercise
protocol and single-leg hop test may be explained by its
more-demanding, and thus more-discriminating nature
when compared with non-fatigued hop testing.
There are several possible reasons for the fact that,
when fatigued, patients performed worse using the involved leg during single-leg hop testing. Firstly, several
studies, including this one, have demonstrated that individuals with ACL injury or reconstruction scored within a
normal range during single-leg hop tests, yet showed reduced quadriceps strength [7, 11, 31]. It has been suggested that this is due to the hip and ankle extensors being
capable of compensating for a knee-extension moment
deficit in the involved extremity [11]. However, it is pos-
Table 1 Comparisons of single-leg hop performance under different test conditions and 1 RM knee-extension strength
Test difference
Involved
side
Non-involved
side
Hop or strength
index
Percentage
between sides
Non-fatigued hop condition (cm)
Fatigued hop condition (cm)
1 RM strength (kg)
141±21
109±21
53±8
145±22a
121±21b
62±11b
97±5c
89±8
86±9
3
11
14
aDifferent
from involved side, p<0.05
from involved side, p<0.01
cDifferent from fatigued hop index, p<0.01
bDifferent
354
sible that, during the fatigued-hop conditions in our study,
the hip and ankle extensors were not able fully to compensate for the distinct quadriceps-strength deficit of the
involved leg.
Another possible reason for patients performing worse
using the involved leg during fatigued single-leg hop testing is that the knee joint provides the major energy-absorption function during the landing phase of the singleleg hop (J. Augustsson et al., submitted). We observed that
absorbed power was two to three times greater for the knee
than for the hip, and five to ten times greater for the knee
than for the ankle during landing in both fatigued and nonfatigued test conditions in healthy subjects (J. Augustsson
et al., submitted). The task of landing during the fatiguedhop condition, using the involved leg, therefore presumably led to great difficulties, on both a central and a peripheral level, for the patients after ACL reconstruction.
In order to assess whether a safe return to sports or
strenuous work is possible following ACL reconstruction,
the ability to perform functional tests of the lower extremity within normal values is regarded as an important criterion [14]. Currently, however, there is no clear consensus
with regard to the definition of normal range in functional
tests. For example, no single standard symmetry index is
used for determining normal or abnormal maximal hoptest ability in knee rehabilitation. A ratio of limb symmetry known as the limb symmetry index (LSI) has been the
most frequently reported criterion for assessing whether a
hop test is normal or abnormal [1]. The LSI is used to calculate the difference in hop length between the injured and
uninjured sides. An LSI of 15% – i.e. a 15% difference
between limbs – is often regarded as satisfactory for single-leg hop tests [7]. However, it should be noted that
these values were empirically established by noting that
90% of subjects without a history of ACL injury had LSIs
greater than or equal to 85% [7]. Juris et al. [19] on the
other hand, noted hop-symmetry scores of 90% for the
single-leg hop test in healthy subjects. Moreover, it has
been reported that in individuals with ACL-deficient knees
only those performing at more than 90% of knee function
(including the single-leg hop test) compared with the uninjured side were able successfully to return to pre-injury
levels of activity [13]. Although the degree of difference
in performance between the two lower extremities has not
been shown to have a definite relationship with a propensity towards injury during athletic activities [32], a difference of 10% or more can be considered to reflect a real
difference in the capacity of performance [26]. Taken together, we regard a side-to-side difference of more than
10% between the involved and non-involved leg following ACL reconstruction as unsatisfactory for both hopand strength-test scores, and believe that it may predispose a patient to overuse and/or acute injuries when returning to sports or strenuous work.
In our study, patients with ACL reconstruction exhibited a significant knee-extension 1-RM strength deficit
(p<0.01). In accordance with this, persistent quadriceps
weakness seems to be common in the ACL-reconstructed
leg despite “aggressive” rehabilitation [2, 3, 8, 11, 16, 20,
22, 24, 30, 34]. In a recent study, Carter and Edinger [8]
were intrigued to find that only half of the competitive
athletes in their study had accomplished 80% or greater
leg strength of the ACL-operated leg by 6 months after
surgery, as it is customary to allow return to full activities
at that time, with some authors advocating return to sports
as early as 4 months after the procedure [9, 17]. In our
study, 63% of the patients had residual quadriceps-muscle
weakness 11 months after surgery, yet 69% had returned
to their previous level of sports participation. We conclude that patients may return to sports 11 months postoperatively, but that leg strength is frequently not adequate
at that time to do so without running the risk of re-injuring the knee.
We used the 1-RM test to compare the knee-extension
strength of the involved and the non-involved side and
found excellent test-retest reliability (the ICC value was
0.96 for the involved and the non-involved side). This is
in accordance with the results of Hennessy and Watson
[15], who noted high reliability for the 1-RM test for the
bench press and the barbell squat exercise (r=0.96 and
0.97 respectively) in healthy subjects. Although the isotonic 1-RM test is the most frequently-used tool for the
evaluation of muscle strength in sports [21], strength in
knee rehabilitation is almost always evaluated with isokinetic dynamometry [2, 3, 7, 8, 9, 16, 20, 23, 24, 31, 34].
However, according to several studies [4, 28, 33], isokinetic tests are not sensitive to isotonic weight-training
strength improvements. The rationale for performing isokinetic tests in clinical practice is therefore somewhat
weak, as weight training during rehabilitation is typically
performed using free weights and weight machines in an
isotonic mode only.
The movement velocity during the exhaustive knee-extension exercise set was not controlled in our study. This
is due to the fact that the cadence consistently decreases
from the first to the last repetition for a subject during a
set of heavy weight-training exercise [18].
Conclusion
Although injuries tend to occur more frequently at the end
of a sporting event, when a participant is fatigued [10, 12,
35], patients are typically examined for return to sports
using functional tests performed under non-fatigued conditions. This may compromise the therapist’s ability to decide whether a patient with ACL reconstruction can safely
return to sports or strenuous work activities. In accordance
with this, no patients in our study displayed abnormal hop
symmetry when non-fatigued; however, two-thirds showed
abnormal hop symmetry for the fatigued test condition. It
is concluded that the pre-exhaustion exercise protocol
355
combined with the single-leg hop test improved testing
sensitivity when evaluating lower-extremity function after
ACL reconstruction. For a more realistic approach, when
it comes to the functional performance testing of patients
after ACL reconstruction it is suggested that these tests
should be performed both under non-fatigued and fatigued test conditions.
Acknowledgements This study was supported by a grant from
the Swedish National Centre for Research in Sports. We declare
that the experiments performed in our study comply with the laws
of Sweden.
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