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Biomechanics Laboratories Utilizing the Kinematic Measurement System
Laboratory 1
Stretch Shorten Cycle Capacity
Equipment

4 x contact mats and KMS interfaces

4 x computers with Kinetic Measurement System (KMS) Software

16 x 25cm step benches
Note: lab can be completed with just a single KMS if required.
Introduction
Most human movement activities involve a counter movement during which the
muscles involved are first stretched and then shortened to accelerate the limb. This
action of the muscle is called a stretch shortening cycle (SSC) (Komi, 1986) and
involves some interesting neural and mechanical processes. A great deal of research
has been directed toward the study of the stretch shortening cycle (Bosco & Komi,
1979; Bosco, et al., 1982; Ettema, et al., 1990; Gollhofer & Kyroelaeinen, 1991;
Hakkinen, 1989; Komi, et al., 1982; Schmidtbleicher, 1988) because it has been
observed that jump performance is potentiated by the prestretch experienced
during a counter movement jump (Bosco & Komi, 1979). One study by Bosco et al.
(1982) found differences between squat jump (SJ) and counter movement jump
(CMJ) heights of 18%-20%. The CMJ jump is higher because as the jumper
approaches the end of the decent, the muscle begins to act eccentrically to slow the
body and initiate the upwards movement. As the muscle is activated, force is
increased in the tendomuscular complex increasing its stiffness or resistance to
stretching. The result is a storage of elastic energy in the muscle and tendon which
is recovered during the subseqent concentric phase making it more powerful (Bosco
& Komi, 1979). Also contributing to the potentiation of the concentric muscle action
is a reflex increase in neural stimulation to the muscle, brought about by the sudden
stretch stimulus (Gollhofer & Kyrolainen, 1991; Schmidtbleicher, et al., 1988).
Studies by Bosco and Komi (1979) demonstrate that jump performance increases
with increasing stretch loads applied. For example, during drop jumping, the height
of the subsequent jump increases with increases in drop height. This occurs only up
to a point.
There is a threshold at which the stretch load is too great and the golgi tendon organ
reflex causes an inhibition of muscle contraction reducing the jump height attained
(Gollhofer & Kyrolainen,1991; Schmidtbleicher et al., 1988). It should be noted that
athletes unaccustomed to intense SSC loads may produce his/her best performance
during a CMJ and the drop jump heights will be even lower than the SJ
(Schmidtbleicher, 1992).
Practical Exercise A
1. Divide into 4 groups of 4 students
2. Select one student to be the subject and instruct them in a 5 minute warmup for
the lower body.
3. Instruct the subject to perform three SJ's and three CMJ's and record the height
jumped for each. Alternate between SJ and CMJ to reduce order effects. Ensure that
the subject does not perform any dip movement prior to the SJ. All jumps should be
completed with the hands on the hips and maximal height should be attempted.
Squat Jump Height (m)
Trial 1
Trial 1
Trial 1
Average
Counter Movement Jump Height (m)
Study Questions:
What was the percentage difference between SJ and CMJ heights?
How does this result compare with that of the literature?
What type of training methods could be used to increase the subject’s ability to
utilize the stretch shortening cycle?
Practical Exercise B
Drop jump training is a common form of plyometric drill. By increasing the height of
drop, one can increase the stretch load imposed on the muscle. Depending on the
training history of the athlete greater drop height should result in higher
subsequent jump as they are able to utilize the increased stretch load to facilitate
impulse applied to the ground and so increased takeoff velocity and therefore jump
height. However, they will reach a drop height at which the tension in the
musculotendinous units of the lower limbs will exceed the threshold of the Golgi
tendon organs initiating a reflex to limit force production so as to protect the muscle
and tendon. This reflex causes inhibition of the primary neural drive, reducing
muscle force production and therefore jump height. Athletes with limited training
history in high tension stretch shortening cycle movements may produce the
greatest jump height from the ground, a zero drop height which is a counter
movement jump or a relatively low drop height of 10 to 20 cm (Figure 1).
Reactive Strength Index
The ability to tolerate very high stretch loads without reflex inhibition is termed the
reactive strength index (RSI) and is an excellent measure of an athlete’s ability in the
stretch shorten cycle. The reactive strength index is generally calculated in two
ways:
RSI = flight time / contact time
RSI = jump height / contact time
Regardless of the method chosen the two are essentially identical as there is a
perfect relationship between the two calculations.
jump height (cm)
trained good
good
poor
cmj
30
45
60
75
drop height (cm)
Figure 1. Relationship between drop height and jump height for different levels of
athlete and training history.
In this activity, use the contact mat to measure jump heights and contact times from
0.25m, 0.50m, 0.75m and 1.0m drop heights. Complete three trials at each height
and record the trial with the highest jump height.
Drop Height
Contact time
Flight time
Jump height
RSI
0
0.25
0.50
0.75
1.0
Plot a graph of contact time and flight time versus drop height.
Plot a graph of RSI versus drop height.
What was the effect of increasing drop height on contact time and jump height?
What would be the significance of the results if one athlete produced the greatest
jump height from the 0.5 m drop height and a second athlete who produced the
greatest jump height during the CMJ with no drop?
Laboratory 2
Load Velocity Power Relationship
Equipment

4 contact mats and KMS interfaces

4 computers with Kinetic Measurement System Software

4 pairs of dumbells: 5kg, 10kg, 15kg and 20kg each (weights may be varied
depending on strength of subject)
Note: lab can be completed with just a single KMS if required.
Introduction
The predominant requirement in a large number of sports is explosive power. For
the lower body this is perhaps best exemplified in the vertical jump. Here the
muscles about the hip, knee and ankle act rapidly and with high force to produce the
greatest possible velocity of the body as it leaves the ground. The jump height
produced is determined purely by this takeoff velocity. This laboratory session
addresses the interaction of load, velocity and power during vertical jump
performance and illustrates their significance to the testing and training of human
performance in general.
Strength Versus Power
Strength is the ability of the muscle to exert a high force or torque at a specified
velocity (Knuttgen & Kraemer, 1987) and varies for different muscle actions such as
eccentric, concentric and isometric (Kraemer, 1992). Dynamic strength is often
assessed using a 1 repetition maximum (1RM) test in which strength is assessed as
the maximum weight the athlete can lift once through the complete movement. The
development and assessment of strength has received a great deal of research
attention (Atha, 1981; Berger, 1962; Hakkinen, et al., 1987; Schmidtbleicher, 1988)
and the interested reader may refer to the relevant literature. Pure 1RM strength
however, is a requirement of a limited number of athletic endeavours (e.g., Power
Lifting). Most sports require the explosive application of force to accelerate the
body, limb or implement resulting in a high velocity at the point of impact or release.
This aspect of performance has been termed explosive power or speed strength
(Young, 1993).
The key difference between strength and power in concentric movements is the
speed of muscle action. Strength is the force that the muscle can exert and is
maximized during very slow concentric muscle actions. This is due to the force
velocity relationship for muscle (Figure 2.) The faster the velocity of concentric
muscle action, the lower the force that can be produced (Hill, 1938). Pure 1RM
strength is required in the sport of Power Lifting because there is no requirement
for the weight to be lifted quickly as the athlete is attempting to lift the maximum
amount of weight. This requires movement velocities which are just higher than
zero. However, most human sporting activities occur at faster velocities of
movement.
In terms of testing and training, velocity specific effects are apparent (Kaneko, et al.,
1983; Moritani, et al., 1987; Newton & Wilson, 1993). Therefore, strength testing
using heavy loads and low velocity of movement may have limited predictive ability
to high speed performance. Thus, it may be much more useful to assess force and
power output at or near the velocity of movement used in the event. In terms of
training, a number of studies have shown limited performance improvements in
explosive activities resulting from heavy strength training (Hakkinen, et al., 1985a;
Wilson, et al., 1993) and it may be much more effective to train with lighter loads
using explosive ballistic movements.
A number of studies (Faulkner, et al., 1986; Hill, 1938, Newton & Wilson , 1993)
have shown that mechanical power output is maximized at approximately 30% of
maximum shortening velocity and a load of 30% of maximum isometric strength
(MVC). Because of this relationship, the 30% MVC load has been proposed as the
optimal load for the development of mechanical power (Kaneko et al., 1983; Wilson
et al., 1993) and have suggested that ballistic weight training should be performed
using this load. The optimal load can be determined for squat jumps using the load
height test proposed by Bosco (1992).
Figure 2. Force velocity power relationship for skeletal muscle. Vm, Pm and Fm are
maximum movement velocity, maximum power output and maximum isometric
force output respectively (adapted from Faulkner, et al., 1986).
Here the athlete performs CMJ's with increasing additional loads. The height of jump
and power output is recorded and the load which produced the greatest power
output is determined.
Practical Exercise A
1. Divide into 4 groups of 4 students
2. Select one student to be the subject and instruct them in a 5 minute warmup for
the lower body.
3. Instruct the subject to perform three CMJ's with no additional load as well as each
of the four loads. Exchange dumbells with the other groups and randomise the
order. All jumps should be completed with the hands on the hips and maximal
height should be attempted. For the dumbell trials, the weights should be held in the
hands, firmly against the hips. Make sure that you add the weight to the subject's
body weight and enter it into the KMS so that power can be correctly calculated.
4. Record the height jumped and power output for each trial.
Load (kg)
Jump Height (m)
Jump Power (W)
0
5
10
15
20
Plot a graph of jump height and power against load.
Discuss why the graph above is similar to the force, velocity, power graph typical of
skeletal muscle.
What was the optimal load for power output? Why is this significant?
Discuss the theoretical effects on the graph above if the subject completed a
program of heavy weight training versus explosive jump training.
Laboratory 3
Biomechanics of Plyometric Training
Equipment

4 x contact mats and KMS interfaces

4 x computers with Kinetic Measurement System (KMS) Software

16 x 25cm step benches
Introduction
Vertical jump performance has been shown to respond to training which involves
the athlete performing SSC movements with a stretch load greater and more rapid
than to which they are accustomed. These activities have been termed plyometrics
and have been found, in a number of studies, to be effective for increasing jumping
ability (Adams, et al., 1992; Clutch, et al., 1983; Schmidtbleicher, et al., 1988; Wilson,
et al., 1993). Plyometric training results in an increase in the overall neural
stimulation of the muscle and thus force output, however, qualitative changes are
also apparent.
In subjects unaccustomed to intense SSC loads, there is a reduction in EMG activity
starting 50-100 ms before ground contact and lasting for 100-200 ms
(Schmidtbleicher, et al., 1988). Gollhofer (1987) has attributed this to a protective
mechanism by the golgi tendon organ reflex acting during sudden, intense stretch
loads to reduce the tension in the tendomuscular unit during the force peak of the
SSC. After a period of plyometric training the inhibitory effects are reduced, termed
disinhibition, and increased SSC performance results (Schmidtbleicher, et al., 1988).
Practical Exercise A
1. Divide into 4 groups of 4 students
2. Select one student to be the subject and instruct them in a 5 minute warmup for
the lower body.
3. Instruct the subject to perform drop jumps from the bench. Three conditions are
to be completed:
1. Attempt to minimise the time spent on the ground (contact time);
2. Attempt to maximise the jump height;
3. Attempt to maximise the jump height while minimising the contact time.
Complete three trials of each condition and record the best performance for each
condition. All jumps should be completed with the hands on the hips
4. Record the height jumped, contact time and power output.
Condition
Contact Time
Flight time
Jump Height
Jump Power
(ms)
(ms)
(m)
(W)
1
2
3
Power output is calculated as: Power = mgh / time
Where:
m = mass of subject
g = acceleration dur to gravity (9.81 m.s-2)
h = height of jump calculated from flight time
t = contact time prior to jump
Which jump condition resulted in the greatest power output? Explain why.
Discuss why it is important to minimise the contact time during plyometric training.
Practical Exercise B
Use the contact time test on the Kinematic Measurement System to determine the
average contact time for various activities. Record the contact time for each person
in the group completing:
1. Double leg broad jump off the mat with a run-up;
2. Single leg broad jump off the mat with a run-up;
3. Sprint running over mat (place carpet or rubber over mat to prevent sliding).
Record the average contact time for your group for each activity in the table below.
Condition
Contact Time (ms)
double leg takeoff broad jump
single leg takeoff broad jump
sprint running
Discuss the differences in plyometric training for sprinting versus vertical jump in
terms of contact time.
How do the contact times measured in Exercise A compare to the contact times
during actual sport activities?
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