Download Resultant muscle torque and electromyographic activity during high

This article was downloaded by: [SAIED JALAL ABOODARDA]
On: 11 November 2011, At: 09:27
Publisher: Taylor & Francis
Informa Ltd Registered in England and Wales Registered Number: 1072954 Registered office: Mortimer House,
37-41 Mortimer Street, London W1T 3JH, UK
European Journal of Sport Science
Publication details, including instructions for authors and subscription information:
http://www.tandfonline.com/loi/tejs20
Resultant muscle torque and electromyographic
activity during high intensity elastic resistance and
free weight exercises
a
b
c
Saied Jalal Aboodarda , Mohamad Shariff A. Hamid , Ahmad Munir Che Muhamed ,
d
Fatimah Ibrahim & Martin Thompson
e
a
Sports Centre, University of Malaya, Kuala Lumpur, Malaysia
b
Faculty of Medicine, University of Malaya, Malaysia
c
Advanced Medical and Dental Institute, University Sains Malaysia, Malaysia
d
Department of Biomedical Engineering, University of Malaya, Kuala Lumpur, Malaysia
e
Discipline of Exercise and Sport Science, University of Sydney, Sydney, Australia
Available online: 11 Nov 2011
To cite this article: Saied Jalal Aboodarda, Mohamad Shariff A. Hamid, Ahmad Munir Che Muhamed, Fatimah Ibrahim &
Martin Thompson (2011): Resultant muscle torque and electromyographic activity during high intensity elastic resistance and
free weight exercises, European Journal of Sport Science, DOI:10.1080/17461391.2011.586438
To link to this article: http://dx.doi.org/10.1080/17461391.2011.586438
PLEASE SCROLL DOWN FOR ARTICLE
Full terms and conditions of use: http://www.tandfonline.com/page/terms-and-conditions
This article may be used for research, teaching, and private study purposes. Any substantial or systematic
reproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in any form to
anyone is expressly forbidden.
The publisher does not give any warranty express or implied or make any representation that the contents
will be complete or accurate or up to date. The accuracy of any instructions, formulae, and drug doses should
be independently verified with primary sources. The publisher shall not be liable for any loss, actions, claims,
proceedings, demand, or costs or damages whatsoever or howsoever caused arising directly or indirectly in
connection with or arising out of the use of this material.
European Journal of Sport Science
2011, 1"9, iFirst article
Resultant muscle torque and electromyographic activity during high
intensity elastic resistance and free weight exercises
SAIED JALAL ABOODARDA1, MOHAMAD SHARIFF A. HAMID2, AHMAD MUNIR CHE
MUHAMED3, FATIMAH IBRAHIM4, & MARTIN THOMPSON5
1
Sports Centre, University of Malaya, Kuala Lumpur, Malaysia, 2Faculty of Medicine, University of Malaya, Malaysia,
Advanced Medical and Dental Institute, University Sains Malaysia, Malaysia, 4Department of Biomedical Engineering,
University of Malaya, Kuala Lumpur, Malaysia, and 5Discipline of Exercise and Sport Science, University of Sydney,
Sydney, Australia
Downloaded by [SAIED JALAL ABOODARDA] at 09:27 11 November 2011
3
Abstract
The purpose of this study was to quantify and compare Resultant Muscle Torque (RMT) and muscle activation (EMG)
pattern, during resistance exercise comprising eight repetitions maximum (8 RM) biceps curl with elastic resistance and free
weight exercise. Sixteen male and female recreationally active subjects completed 8 RM biceps curl by each of three
modalities of resistance exercise: (i) dumbbell (DB), (ii) elastic tubing with original un-stretched length at the
commencement of contraction (E0), and (iii) elastic tubing with 30% decrement of original length (E30) at the
commencement of contraction. The magnitude of muscle activation, external force, acceleration as well as range of motion
(ROM) were quantified and synchronised by specific software. The data were collected from all eight repetitions but the first
(initial), the fifth (middle) and the eighth (last) repetitions were selected for further data analysis. Each selected repetition
was partitioned into a concentric and eccentric phase and then each phase was further divided into three equal segments
(3 concentric and 3 eccentric ! 6 segments per repetition). The EMG and RMT data demonstrated a bell-shaped muscle
activation and muscle torque production pattern for the three modes of exercise. The E30 resulted in 15.40% and 14.89%
higher total EMG (mV) as well as 36.85% and 17.71% higher RMT (N ! m) than E0 and DB, respectively (all P B0.05).
These findings support the contention that an elastic resistance device (E30) has the capacity to provide an appropriate high
resistance stimulus to meet the training requirement of elite athletes.
Keywords: Resistance training, elastic tubing, variable exercises, multiple repetitions maximum
Introduction
Resistance training employing free weights or specially designed machines with pulley weights or
hydraulics is a widely practised form of physical
activity for stimulating skeletal muscle hypertrophy
and strength (Baechle & Earle, 2000; Fleck &
Kraemer, 2004). This equipment is both cumbersome and costly. Among various strength training
modalities, Elastic Resistance (ER) is known as a
safe and affordable mode of exercise which can be
adapted to meet the needs of diverse populations
(Page & Ellenbecker, 2003). Numerous research
studies have recommended ER for regeneration of
muscle strength in rehabilitation settings (Hostler et
al., 2001; Kluemper, Uhl, & Hazelrigg, 2006;
Schulthies, Ricard, Alexander, & Myrer, 1998).
However, tensile force of elastic material offers an
ascending external resistance curve which has been
acknowledged by sport scientists (Anderson, Sforzo,
& Sigg, 2008; Wallace, Winchester, & McGuigan,
2006).
The benefits of this ascending elastic force can be
substantiated in exercises such as biceps curl and
shoulder abduction. In this category of exercises, the
torque generating capacity of prime movers is greater
at the beginning of the concentric phase (Harman,
2000). However when using a conventional constant
external resistance (e.g. free weights), muscles accelerate the force and create a moment of torque which
shifts to the late concentric phase and reduces
muscle stimulation (Hodges, 2006). In contrast to
using free weights, the increment of provided external force by elastic material (due to further
elongation) requires the active muscle to develop
tension over the entire concentric phase (Hodges,
Correspondence: Saied Jalal Aboodarda, University Malaya, Sport Centre, PJ. Kuala Lumpore, 56000 Malaysia.
E-mail: [email protected]
ISSN 1746-1391 print/ISSN 1536-7290 online # 2011 European College of Sport Science
http://dx.doi.org/10.1080/17461391.2011.586438
Downloaded by [SAIED JALAL ABOODARDA] at 09:27 11 November 2011
2
S.J. Aboodarda et al.
2006). While providing an ascending resistance
curve, an elastic device has been shown to provide
a bell-shaped torque curve which is compatible with
torque generating capability in many human movements including the biceps curl (Hughes, Hurd,
Jones, & Sprigle, 1999; Simoneau, Bereda, Sobush,
& Starsky, 2001).
Although these findings validate using ER for this
category of exercises, the practical difficulty of
providing a high elastic resistance, particularly at
the beginning of the concentric phase, has limited
the use of ER in high intensity training protocols
(Ebben & Jensen, 2002). Accordingly, two strategies
are recommended for increasing resistance of the
elastic device; 1) reducing the initial length of the
elastic material (Treiber, Lott, Duncan, Slavens, &
Davis, 1998); and 2) using additional elastic bands
in parallel to the current elastic device (Page et al.,
1993). We hypothesised that by applying these two
strategies, significantly higher muscle activation and
muscle torque production could be achieved with an
ER device compared with conventional free weights
when performing high resistance exercises.
This study, was thus undertaken to investigate the
electromyographic muscle activity (EMG) and Resultant Muscle Torque (RMT) profile during the
performance of an eight repetition maximum (8
RM) biceps curl exercise using free weights and
elastic devices.
Methods
Experimental approach to the problem
In this investigation, subjects completed a series of
8-RM biceps curl by three modalities of resistance
exercises comprising: (i) free weights-dumbbell
(DB), (ii) elastic tubing with initial length (E0) and
(iii) elastic tubing with 30% decrement of initial
elongation (E30). The level of muscle activation and
kinetic and kinematic values such as external force,
linear acceleration and range of motion (ROM) were
collected and synchronised by data acquisition
package Myoresearch-XP (Noraxon, Scottsdale,
USA, Master Edition). The first (initial), the fifth
(middle) and the eighth (last) repetitions were
selected for further analysis.
Table I. Physical characteristics of subjects participating in the
study.
Subjects
Age
Percent
Height (cm) Mass (Kg) body fat (%)
Male (n ! 10) 24.492.9 178.396.8 77.395.7
Female (n ! 6) 27.294.8 158.994.7 61.195.7
13.293.9
17.397.4
main testing session. They had no history of injury or
surgery, and were not currently receiving medical
treatment. This experiment was approved by the
Ethics Committee of the Sport Centre, University
Malaya.
Equipment
The neuromuscular activation pattern during 8-RM
Biceps curl exercise was measured via electromyography (EMG) of the biceps brachii muscle with a
sample rate of 1000 Hz using a 16-bit acquisition
mode with an eight-channel TeleMyoTM 2400T G2
EMG system (Noraxon, Scottsdale, Arizona, USA).
The EMG signals were passed through inbuilt
preamplifier leads with Input impedance !100
MV with common mode rejection ratio !80 dB. A
receiver unit collected the telemetry signals from the
receiver and amplified and filtered (15 Hz to 1000
Hz) the signals. The range of motion of the
dominant elbow was monitored using a 2-D electrogoniometer (Noraxon, Scottsdale, Arizona, USA).
A 2-D accelerometer (10g; Noraxon, Scottsdale,
Arizona, USA) was placed over the lateral side of
the wrist to measure linear acceleration of the
forearm and hand in the X and Y axis. The external
resistance of the elastic device was measured using a
force transducer (Noraxon, Scottsdale, Arizona,
USA) placed in series with the elastic device. Data
were collected and synchronised using the data
acquisition package Myoresearch-XP, Master Edition (Noraxon, Scottsdale, Arizona, USA). Before
testing, sensors were calibrated based on the recommended instructions of the manufacturer. The
elastic tubing (yellow, red, green, blue, black and
silver; Hygienic Corporation, Akron, OH) and
standard dumbbell (MuJo Products) were used as
training apparatuses.
Experimental protocol
Subjects
Sixteen healthy male (n !10) and female (n ! 6)
recreationally active volunteers gave their informed
consent to participate in this study. Their physical
characteristics are presented in Table I. The subjects
had no experience of resistance training in the past
12 months and were requested to abstain from any
exercises involving arm muscles 48 hours before the
Physical characteristics of subjects. All subjects attended a preliminary testing session where anthropometric measurements including height, body mass
and the length of the subject’s dominant forearm
(distance from the elbow joint to the wrist joint) and
forearm plus hand (tip of middle finger of the hand
to the elbow) were undertaken and recorded from
the subjects. The percentage of body fat was assessed
Muscle torque and electromyographic activity
Downloaded by [SAIED JALAL ABOODARDA] at 09:27 11 November 2011
using a four-skinfold site (thigh, triceps, suprailiac,
and abdomen) equation (Jackson & Pollock, 1978).
Elastic resistance device. The resting un-stretched
length of E0 was determined for each subject by
measuring the distance from the origin (ground) to
the axis (distal end of the load cell attached to the
handle of the elastic device held by the subject
standing in anatomical position). The resting length
of E30 was therefore calculated as the length of E0 "
30%. The subjects were then familiarised with the
testing procedure by practising maximal voluntary
isometric contractions (MVICs) and dynamic exercises. The resistance required for 8 RM was
assessed by the three types of resistance training
devices (dumbbell, the elastic resistance device at
E0, and E0 length " 30%) prior to the day of testing.
The 8 RM was selected for the current study because
it has been widely recommended for training protocols designed to develop muscle strength (Fry, 2004;
Kraemer et al., 2002). The external load in each
mode of training was either added or removed to
meet the load required for an actual 8 RM. To
achieve this, different combinations of elastic colour
codes were examined for E0 and E30 (each colour
denotes specific resistance; for a review see Simoneau et al., 2001). Accordingly, the colour codes of
E0 and E30 were dictated by the requirement to
successfully complete 8 RM and therefore differed
between the two modes of training. The actual 8 RM
was achieved within the first or second trial.
To avoid inaccurate location of electrodes from
day to day testing, all data were collected within one
testing session. The test protocol began with a 5-min
warm up consisting of 30s to 60s biceps curl exercise
with minimal resistance followed by stretching of the
upper limb musculature. Subjects then rested for 5
minutes during which time the electrogoniometer
and accelerometer were strapped to the subject’s
dominant arm. A pair of surface electrodes (20 mm
interelectrode distance) was placed on the centre of
the muscle belly in the direction of the underlying
muscle fibres as recommended by Hermens et al.
(1999). The ground electrode was placed at the
acromial process. Before placement of electrodes,
the area of skin was shaved, abraded to remove dead
skin with sandpaper and cleaned with alcohol to
decrease skin resistance.
Prior to the dynamic exercises, subjects performed
three MVICs for 5s each at 2-min intervals. Measurements were performed while the subject stood
on a test platform (height: 30 cm), holding the
handle of a non-extensible strap and the elbow was
positioned at 908 (Alway, Grumbt, Stray-Gundersen, & Gonyea, 1992). The MVIC was calculated as
the average amplitude over a one second window of
3
the highest rectified EMG signals (automatically
selected by Myoresearch-XP). This measure became
a reference value (100% EMG) for normalising
muscle activation data during dynamic actions (%
MVIC).
The subjects then completed 8 RM biceps curl
exercises in a randomised order across each of the
three training modalities. Ten to 15 minutes resting
period was assigned between exercise modes. To
control the arm position during dynamic contractions, two laser beams connected to an alarm system
limited the ROM (20"1408 of flexion) at each
extremity. Therefore, an alarm sounded if the subject’s hand extended beyond the laser spectrums.
The cadence of performing the bicep curls was 2s
concentric and 2s eccentric which was maintained by
the auditory signal of a metronome. One second
pause between every repetition was assigned to avoid
potential stretch-shortening cycle interference. An
attempt at 8 RM was deemed successful if all
repetitions were performed in accordance with the
pace of the metronome without any compromise in
ROM, plus failure to complete 9 RM. Ten subjects
were randomly selected to perform the same procedures and protocol 5 days following the test day. The
test-retest reliability for the magnitude of external
force during performance of 8 RM dynamic trials
was 0.89, 0.84 and 0.93 for E30, E0 and DB,
respectively.
The data were collected from all eight repetitions
with the first (initial), the fifth (middle) and the
eighth (last) repetitions selected for further data
analysis. Each of the assigned repetitions was partitioned into a concentric and eccentric phase based
on the end points determined from the electrogoniometer traces. Each concentric and eccentric phase
was divided into three equal segments (3 concentric
and 3 eccentric ! 6 segments per repetition). The
Root Mean Square (RMS) of rectified EMG signals
was computed for each phase of movement. The
average of six segments was used to calculate the
value of every repetition. Finally, the obtained values
from first, fifth and eighth repetitions were used to
calculate the ‘total average EMG’ (average of 6
segments #3 repetitions) for each exercise modality.
The magnitude of Resultant Muscle Torque was
calculated according to the equation recommended
by Enoka (2002). The equation is as follows:
sm ¼ F " D1 þ m " D2 þ Iaþðm " a " dvÞ
þ ðF " a " dyÞ þ ðF " a " dxÞ
þ þðF " a " dyÞ
(1)
Where:
t m ! Resultant Muscle Torque, F !external force,
D1 ! perpendicular horizontal distance from point
4
S.J. Aboodarda et al.
Statistical analyses
Results
EMG (mV)
Figure 1. A schematic of the horizontal distance from point of
applied force to the elbow (D1), the horizontal distance from
centre of mass to the elbow (D2), the distance which centre of
mass and external force pass horizontally on the x axis (dx), and
the distance which centre of mass and external force pass vertically
on the y axis (dy). During elbow flexion, D1 and D2 changes
throughout the biceps curl movement. Therefore, although elastic
force increases with elongation, the actual torque production of
the joint accommodates the ascending-descending characteristics
of most strength curves of joints in the body.
of applied force to axis of rotation, m ! mass of the
segment, D2 ! perpendicular horizontal distance
from centre of mass to axis of rotation, I ! moment
of inertia of the body segment, a ! angular acceleration, a ! acceleration, dx !distance which centre
of mass and external force pass horizontally on the x
axis, and dy ! distance which centre of mass and
external force pass vertically on the y axis. Figure 1
In this equation, the effect of gravity on various
phases of motion was adjusted based on joint angle
and phase of contractions according to the method
recommended by Enoka (2002). In addition, the
direction of acceleration (a) was perpendicular to
the line of the arm and its values were determined
by a 2-D accelerometer on the X and Y axis. The
mass of the forearm plus hand (M) and the location
of the Centre of Mass (CoM) was calculated using
Zatsiorsky’s tables (Zatsiorsky, 2002) and Winter’s
table C9.1 (Winter, 2004), respectively. The moment of inertia (Ia) was determined based on the
equation recommended by Grimshaw, Fowler,
Lees, & Burden (2006). The angular acceleration
(a) was calculated using linear acceleration (measured by accelerometer ! m ! s $2) divided by the
distance of the accelerometer to the axis of rotation
and converted to angular form (rad ! s $2).
The results addressing the total average EMG are
presented in Figure 2. Analysis of variance revealed a
significantly higher value for E30 compared with
both E0 (62920 vs 53920) and DB (62920 vs
55918; P !0.00). No significant difference was
observed between E0 and DB. The differences in
EMG activity between similar segments across the
three modes of exercise are presented in Figure 3 and
Table II.
RMT (N !m)
The results addressing the total average RMT
between modalities of exercise are presented in
Figure 4. Analysis of variance exhibited a significantly higher value for DB compared with E0 (2397
vs 2097; P ! 0.00). In addition, E30 represented a
significantly higher value than both E0 (27910 vs
2097; P !0.00) and DB (27910 vs 2397;
P ! 0.012). The differences in magnitude of force
and RMT between similar segments across the three
80
Mean
70
EMG (%MVC)
Downloaded by [SAIED JALAL ABOODARDA] at 09:27 11 November 2011
Test-retest reliability was evaluated using the data
obtained from the main testing session and the
follow-up testing session (5 days later) and interclass
correlation coefficient (ICC) of average dynamic
force was computed for the three types of training.
The average force, EMG and RMT values during
various segments (1 to 6), repetitions (initial, middle
and end) and modalities of exercise (DB, E0 and
E30) were analysed using a one way analysis of
variance (ANOVA) (SPSS v 15) and post-hoc Bonferroni comparison. Significance was defined as
P B 0.05.
* †
60
50
40
30
20
10
0
DB
E0%
Exercise Modes
E30%
Figure 2. Total average EMG (% of MVIC) within various
exercise modes. The value of every column is comprised of the
average of three repetitions and six segments. * ! E30 is
significantly higher than E0. $!E30 is significantly higher than
DB.
Muscle torque and electromyographic activity
†*
100
90
†
DB
E0
E30
‡ †
40.4
*
Force (N)
40
30
20
100
80
60
40
10
0
20
1
2
3
4
Concentric
5
6
0
1
Eccentric
2
Segments
3
4
Segments
DB
Figure 3. EMG (% of MVIC) within various segments of exercise
modes. The value of every phase comprises of average of
1st%5th%8th repetitions. ! ! DB is significantly higher than
E0. % ! E0 is significantly higher than DB. $!E30 is significantly
higher than DB. # ! DB is significantly higher than E30. * ! E30
is significantly higher than E0.
E0
5
6
E30
Figure 5. The magnitude of applied Force (N) in the three modes
of training within various segments of motion. The value of every
phase includes the average of 1st%5th%8th repetitions. The values
above the E0 and E30 are the mean different between the two
modes of training. ! ! DB is significantly higher than E0.
$ ! E30 is significantly higher than DB. * ! E30 is significantly
higher than E0.
Table II. EMG activity of various segments of motion in the three
modes of exercise.
Total Average EMG (%MVIC)
E0
53.45 (19.71)
60
E30
61.93* (19.98)
Mean (S) of EMG activity for segment of motion(n !16)
1
2
3
4
5
6
70.9
78.2
49.3
30.4
42.2
43.4
! (10.2)
(10.4)
(8.8)
(8)
(9.6)
! (11.4)
54.1 (9.7)
79.2 (10.1)
69.9% (9.2)
45.7% (8.1)
39.7 (9.1)
24.5 (7.7)
67.2* (7.2)
88*$ (6.6)
83.8*$ (6.3)
46.1$ (9.4)
46.6* (13.4)
38.7* (6.7)
Note:The value of every segment includes the average of 1th % 5th
% 8th repetitions. ! ! DB is significantly higher than E0. * ! E30
is significantly higher than E0. $ ! E30 is significantly higher than
DB. % ! E0 is significantly higher than DB.(All in P B0.05).
40
Mean
*†
†*
50
RMT (N . m)
DB
54.90 (18.26)
‡
†*
DB
E0%
E30%
40
30
*
*
20
10
0
1
2
3
4
concentric
5
6
eccentric
Segments
Figure 6. RMT (N ! m) values within various segments of
exercise modes. The value of every segment includes the average
of 1st%5th%8th repetitions. ! ! DB is significantly higher than
E0. % ! E0 is significantly higher than DB. $!E30 is significantly
higher than DB. * ! E30 is significantly higher than E0.
35
modes of exercise are presented in Figures 5 and 6
and Table III.
30
RMT (N . m)
Downloaded by [SAIED JALAL ABOODARDA] at 09:27 11 November 2011
22.5
120
*
50
*
39.0
18.5
140
60
20.8
*
160
70
†
21.3
*
80
EMG (% of MVC)
‡
†*
5
25
20
15
Discussion
10
5
0
DB
E0%
Exercise Modes
E30%
Figure 4. Total average RMT (N ! m) within various exercise
modes. The value of every column is comprised of the average of
three repetitions and six segments. * ! E30 is significantly higher
than E0. $!E30 is significantly higher than DB. ! ! DB is
significantly higher than E0.
The purpose of this descriptive study was to quantify
and compare the electromyographic activity and the
resultant muscle torque pattern between three
modes of resistance training (DB, E0 and E30)
during the performance of high resistance biceps
curl exercises. Previous investigators have speculated
that ER does not elicit maximal activation because
the external force is less than that requiring maximal
activation (Matheson, Kernozek, Fater, & Davies,
6
S.J. Aboodarda et al.
Table III. RMT values in various segments of motion for the
three modes of exercise.
Total Average RMT (N . m)
DB
E0
E30
23.31 ! (7.58)
20.05 (6.64)
27.44*$ (10.21)
Mean (s) of RMT values for segment motion (n !16)
Downloaded by [SAIED JALAL ABOODARDA] at 09:27 11 November 2011
1
2
3
4
5
6
21 ! ( 6.9)
33.7 (3.6)
20.8 (6.5)
21.2 (11.4)
23.3 ! (13.2)
21.4 ! (18.3)
9.1 (7)
34.1 (18)
32.4% (23.4)
21.3 (7.4)
15.4 (7.4)
8.9 (7.9)
16.3* (8.4)
44*$ (5.9)
42.1*$ (8.9)
21.6 (7.89)
20.2 (13)
19* (8.3)
Note: The value of every segment includes the average of
1st%5th%8th repetitions. ! ! DB is significantly higher than
E0. * ! E30% is significantly higher than E0. $ ! E30 is
significantly higher than DB. % ! E0 is significantly higher than
DB. (all in P B0.05).
2001; Page et al., 1993; Hostler et al., 2001). It
should be noted that in the present investigation no
equalisation of external force was performed among
the three modes of training. Instead, subjects completed 8 RM biceps curl by each of the three exercise
modes (DB, E0 and E30). The rationale for selecting
this novel method was based on the fact that: (i) no
scientific method has been established to equalise the
magnitude of external force; and (ii) the repetitions
maximum strategy is known as a popular method for
prescribing high resistance training protocols. A
further consideration was that undertaking 8 RM
was believed to make the research outcomes more
applicable to athletic conditioning.
Total average EMG and RMT
Comparing the values obtained from the three
modes of training (Figures 2 and 4) revealed that
E30 demonstrated 15.40% and 14.89% higher
muscle activation (EMG) and 36.85% and 17.71%
higher muscle torque production (RMT) compared
with E0 and DB, respectively. This highlights the
ability of the elastic device to meet the training
requirement for an elite athlete who needs to practise
with high exercise intensities. In line with our
finding, Matheson et al. (2001) and Muhitch
(2006) concluded that elastic resistance could be
used as a viable alternative to conventional free
weights, provided that adequate external resistance
is applied. Our findings question the recommendations of prior studies that are based on a low tensile
force of elastic material and conclude that the utility
of elastic devices is not confined to applications
centred on rehabilitation (Hintermeister, Lange,
Schultheis, Bey, & Hawkins, 1998; Hostler et al.,
2001).
Theoretically, developing muscle strength has
been closely related to greater force application,
longer duration of muscle tension and a greater total
amount of work (Hortobagyi et al., 1996; Linnamo,
Pakarinen, Komi, Kraemer, & Häkkinen, 2005). In
high resistance weight training the initial gains in
strength are primarily attributed to a greater central
neural drive to the muscle with further subsequent
strength gains associated with muscle hypertrophy
(Moritani, 1992). On this basis, one would expect
that higher total average muscle activation and
muscle torque production in E30 may result in
greater strength gains compared with E0 and DB.
This expectation is premised on there being a direct
relationship between increases in muscle activation
and increases in muscle force. However this relationship may be confounded by muscle-tendon compliance and the activation of some motor units to
maintain stability during the E30 trial. Further
research is required to substantiate this postulate.
EMG and RMT pattern
The present EMG and RMT data acquired from six
segments of contraction demonstrated a bell-shaped
muscle activation and muscle torque production
pattern for the three modes of exercise (Figures 3
and 6). These data support previous findings concluding that although elastic force increases with
elongation, the interaction effects of leverage systems
and the stretch-shortening cycle create an ascendingdescending torque curve which is compatible with
torque generating capability in the elbow flexors
(Lim & Chow, 1998). In this case, shorter moment
arm length (horizontal distance from line of action of
elastic device to the elbow joint) at the beginning and
end of the concentric phase creates a bell-shaped
torque curve with the elastic device, thus making the
lifting motion easier in these areas (Hughes et al.,
1999).
However, the key finding of the present study
concerns the positive influence of manipulating the
initial elastic device length and resistance (and
matching colour codes of elastic material) in achieving higher EMG activity and RMT with the elastic
device. Firstly, it is worth mentioning that in order to
achieve 8 RM exercise intensity, it is inevitable that
additional elastic tubing has to be used in parallel to
the current device. Hughes et al. (1999) reported the
resistance of an elastic device (Hygienic Corporation, Akron, Ohio) from 3.3 N (yellow) to 70.1 N
(silver) when elastic materials were at 18% (minimum) and 159% (maximum) of deformation from
resting length (un-stretched), respectively. These
data indicate that one unit of the commercially
Downloaded by [SAIED JALAL ABOODARDA] at 09:27 11 November 2011
Muscle torque and electromyographic activity
produced elastic tubing cannot possibly provide
adequate external force necessary to accomplish
high exercise resistance training for an elite athlete.
Therefore, matching various colour codes of elastic
material (of different grades of ‘stiffness’) is a basic
strategy to increase the external force required in
using the ER device for training purposes.
Alternatively, the length of elastic material concerned may be shortened to require an increased
force of ‘stretching’ to approximate the force required for training purposes. This approach was
used with the E30 condition which resulted in
significantly higher EMG activity and RMT compared with E0 across all concentric phases (Figures 3
and 6). These data disclose the importance of
reducing the initial length as an essential strategy to
develop muscle activation and torque production
when using an ER device. Thus, although initially
matching elastic colour codes were implemented in
both E30 and E0, this strategy in E0 was insufficient
in eliciting maximal activation of the muscle. In the
eccentric phase however the differences between E0
and E30 diminished (Figures 3 and 6). During the
fourth segment, the forearm is accelerating in the
same direction that elastic force is acting (downward). Since muscle tension must reduce to facilitate
extension motion, the variation of external force
between E30 and E0 does not make any significant
EMG and RMT difference between the two modes
of training. However, to decelerate and to stop the
forearm motion in the fifth and sixth segments,
higher muscle activation is required to overcome
the greater torque generated by E30.
The question that arises regarding the present data
is: ‘How did subjects complete the same number of
repetitions (8 RM) with E0 and E30, although
higher EMG and RMT values were achieved by
E30 (Figures 3 and 6)?’ One might speculate that
due to increased resistance with shorter elastic
tubing (in E30) subjects should not be able to
complete 8 RM. There are several possible explanations for these apparent paradoxical findings. Firstly,
in the present study, the 8 RM was assigned as an
equating criterion between the three modes of
training. On this basis, subjects naturally used less
resistive tubing for E30 to counterbalance the effect
of the shorter length; unless, they were not able to
complete 8 RM. As a result, E0 and E30 provided
different patterns of tensile force across the ROM
(Figure 5). The data indicates that although E30
offers greater force across all phases compared with
E0, only significant differences were observed at the
first and sixth phases (mean difference !40 N,
Figure 5). The two phases (first and sixth) where
there was a significant increase in E30 force compared with E0 were in actual fact the two lowest
forces across the six phases analysed. Although the
7
E30 force was marginally greater compared with E0
across the remaining four phases, this insignificant
increase in force did not provide sufficient stimulus for subjects to exceed their 8 RM. Thus, these
findings suggest that although the interplay between
resistance and length of tubing in E30 could have
resulted in higher EMG and RMT compared with
E0, it was not of a magnitude that changed the
number of repetitions.
Another explanation for subjects achieving 8 RM
in the E30 condition despite overcoming a greater
‘lifting’ resistance may involve a neurophysiological
mechanism whereby a signalling pathway increases
motor unit recruitment to overcome the resistance.
Previous investigations have demonstrated that preloading muscle at the inception of concentric and
end of eccentric phases (what presumably happens
in E30) could stretch the intrafusal muscle fibres,
facilitate greater discharge of efferent impulses to
extrafusal fibres and increase the force of the
contraction in the muscle (Aura & Komi, 1986;
Enoka 2000). In addition, muscle preloading has
been shown to reduce time constants of the stimulation-active state coupling as well as the interaction
between series elastic components and contractile
elements, that helps to enhance muscle stimulation
during the concentric phase (Bobbert, Gerritsen,
Litjens, & Van Soest, 1996). These mechanisms
however have been suggested to increase force
production during exercises involving the stretchshortening cycle (SSC) action (Moore & Schilling,
2005; Sheppard et al., 2008); while in the present
study a one second pause at the transition from
eccentric to concentric phase was designed to
dissipate stored elastic energy within the muscles.
Clearly more investigation is required to determine
the effects of preloading muscle by elastic devices on
the pattern of subsequent muscle force production.
The comparison between E30 and DB also
indicated superiority of E30 in producing considerably higher EMG in the second, third and fourth
segments and greater RMT in the second and third
segments of contraction (Figures 3 and 6). These
data support the hypothesis that the ascending
elastic force curve causes the prime movers to
develop muscle tension across the entire concentric
phase to enable completion of the lifting motion
(Hodges, 2006). However, providing constant external force by DB resulted in reduced muscle
activation and muscle torque production at the end
of the concentric phase. In this case, given that the
torque generating capability of elbow flexors is
greater at the beginning of the concentric phase
(Harman, 2000), the load is accelerated across the
first segment and produces a moment of torque
which would shift to the third segment and reduce
muscle activation. Numerous investigators have
Downloaded by [SAIED JALAL ABOODARDA] at 09:27 11 November 2011
8
S.J. Aboodarda et al.
highlighted this period of low muscle stimulation as
one of the limitations of conventional free weights
(Cronin & Henderson, 2004; Wallace et al., 2006).
These researchers have speculated that the reduction
of muscle tension in the late concentric phase can
constrain strength development in this area of range
of motion. In addition, as demonstrated in Figures 3
and 5, the E30 condition achieved EMG and RMT
values similar to the DB in segments 1and 6. Thus, it
may be that applying E30 could partially offset the
weakness of standard ER exercises in not providing a
high external force to overcome during the early
concentric phase of contraction. Although this study
validates utilising ER for achieving a higher stimulus
for muscle activation among athletes, our comments
are speculative as to whether adaptation to the E30
condition could result in even higher levels of central
neural activation, muscle hypertrophy and increased
strength development.
References
Alway, S.E., Grumbt, W.H., Stray-Gundersen, J., & Gonyea, W.J.
(1992). Effects of resistance training on elbow flexors of highly
competitive bodybuilders. Journal of Applied Physiology, 72,
1512"1521.
Anderson, C.E., Sforzo, G.A., & Sigg, J.A. (2008). The effects of
combining elastic and free weight resistance on strength and
power in athletes. The Journal of Strength & Conditioning
Research, 22, 567"574.
Aura, O., & Komi, P.V. (1986). Effects of prestretch intensity on
mechanical efficiency of positive work on elastic behavior of
skeletal muscle in stretch-shortening cycle exercises.
International Journal of Sport Medicine, 7, 137"143.
Bobbert, M.F., Gerritsen, K.G.M., Litjens, M.C.A., & Van Soest,
A. (1996). Why is countermovement jump height greater than
squat jump height? Medicine & Science in Sports & Exercise,
28(11), 1402"1412.
Cronin, J.B., & Henderson, M.E. (2004). Maximal strength and
power assessment in novice weight trainers. The Journal of
Strength & Conditioning Research, 18(1), 48"52.
Ebben, W.E., & Jensen, R.L. (2002). Electromyographic and
kinetic analysis of traditional, chain, and elastic band squats.
The Journal of Strength & Conditioning Research, 16, 547"550.
Enoka, R. (2002). Neuromechanics of human movement (3rd ed).
Champaign, IL: Human Kinetics.
Fleck, S.J., & Kraemer, W.J. (2004). Designing resistance training
programs. Champaign, IL: Human Kinetics.
Fry, A.C. (2004). The role of resistance exercise intensity on
muscle fiber adaptations. Sport Medicine, 34, 663"679.
Grimshaw, P., Fowler, N., Lees, A., & Burden. A. (2006). Sport
and exercise biomechanics. Taylor and Francis Inc. United State.
Harman, H. (2000). The biomechanics of resistance exercise. In
T.R. Baechle, & R.W. Earle (Eds.), Essentials of strength training
and conditioning (pp. 26"56). Champaign, IL: Human Kinetics.
Hermens, H.J., Freriks, B., Merletti, R., Hägg, G.G., Stegeman,
D., Blok, J., Rau, G., & Disselhorst-Klug, C. SENIAM 8:
European Recommendations for Surface ElectroMyoGraphy,
deliverable of the SENIAM project. Roessingh Research and
Development b.v., 1999, ISBN: 90-75452-15-2.
Hintermeister, R.A., Lange, G.W., Schultheis, J.M., Bey, M.J., &
Hawkins, R.J. (1998). Electromyographic activity and applied
load during shoulder rehabilitation exercises using elastic
resistance. The American Journal of Sports Medicine, 26(2),
210"220.
Hodges, G.N. (2006). The effect of movement strategy and elastic
starting strain on shoulder resultant joint moment during elastic
resistance exercise. Manitoba, Canada: University of Manitoba
(Unpublished Thesis).
Hopkins, J.T., Christopher, D.I., Michelle, A.S., & Susan, D.B.
(1999). An electromyographic comparison of 4 closed chain
exercises. Journal of Athletic Training, 34(4), 353"357.
Hostler, D., Schwirian, C.I., Campos, G., Toma, K., Hagerman,
F.C., & Staron, R.S. (2001). Skeletal muscle adaptation in
elastic resistance training young men and women. European
Journal of Applied Physiology, 86, 112"118.
Hortobagyi, T., Barrier, J., Beard, D., Braspennincx, J., Koens, P.,
Devita, P., et al. (1996). Greater initial adaptations to
submaximal muscle lengthening than maximal shortening.
Journal of Applied Physiology, 81, 1677"1682.
Hughes, C.J., Hurd, K., Jones, A., & Sprigle, S. (1999).
Resistance properties of Thera-Band† tubing during shoulder
abduction exercise. Journal of Orthopedic and Sports Physical
Therapy, 29(7), 413"420.
Jackson, A.S., & Pollock, M.L. (1978). Generalized equation for
predicting body density of men. British Journal of Nutrition, 40,
497"504.
Kluemper, M., Uhl, T.L., & Hazelrigg, H. (2006). Effect of
stretching and strengthening shoulder muscles on forward
shoulder posture in competitive swimmers. Journal of Sport
Rehabilitation, 15(1), 58"70.
Kraemer, W.J., Dudley, G.A., Dooly, C., Feignbaum, M.S.,
Fleck, S.J., Franklin, B., et al. (2002). Progression models in
resistance training for healthy adults. Medicine & Science in
Sports & Exercise, 34, 364"380.
Kraemer, W.J., & Ratamess, N.A. (2004). Fundamentals of
resistance training: Progression and exercise prescription.
Medicine & Science in Sports & Exercise, 36, 674"688.
Kraemer, W.J., & Ratamess, N.A. (2005). Hormonal response
and adaptation to resistance exercise and training. Journal of
Sport Medicine, 35, 339"361.
Kroon, G.W., & Naeije, M. (1991). Recovery of the human biceps
electromyogram after heavy eccentric, concentric or isometric
exercise. European Journal of Applied Physiology, 63(6), 444"
448.
Lim, Y., & Chow, J. (1998). Electromyographic comparison of
biceps curls performance using a dumbbell and an elastic
tubing. Paper presented at the North American Congress on
Biomechanics, Waterloo, Canada.
Linnamo, V., Newton, R.U., Häkkinen, K., Komi, P.V., Davie, A.,
McGuigan, M., et al. (2000). Neuromuscular responses to
explosive and heavy resistance loading. Journal of Electromyography and Kinesiology, 10, 417"424.
Linnamo, V., Pakarinen, A., Komi, P., Kraemer, W., & Häkkinen,
K. (2005). Acute hormonal responses to submaximal and
maximal heavy resistance and explosive exercises in men and
women. Journal of Strength and Conditioning Research, 19(3),
566"571.
Matheson, J.W., Kernozek, T.W., Fater, D.C.W., & Davies, G.J.
(2001). Electromyographic activity and applied load during
seated quadriceps exercises. Medicine & Science in Sports &
Exercise, 33, 1713"1725.
Moore, C.A., & Schilling, B.K. (2005). Theory and application of
augmented eccentric loading. Strength and Conditioning Journal,
27(5), 20"27.
Moritani, T. (1992). Time course of adaptations during strength
and power training. In P.V. Komi (Ed.), Strength and power in
sport (pp. 266"278). Oxford: Blackwell Scientific.
Muhitch, L. (2006). Electromyographic investigation of free weights
and Thera-Band. State University of New York College at
Cortland, New York, USA (Unpublished Thesis).
Muscle torque and electromyographic activity
Downloaded by [SAIED JALAL ABOODARDA] at 09:27 11 November 2011
Newsam, C., Leese, C., & Fernandez-Silva, J. (2005). Intratester
reliability for determining an 8-repetition maximum for 3
shoulder exercises using elastic bands. Journal of Sport
Rehabilitation, 14(1), 35"47.
Page, P., & Ellenbecker, T. (2003). The scientific and clinical
application of elastic resistance. Champaign, IL: Human Kinetics.
Page, P., Lamberth, J., Abadie, B., Boling, R., Collins, R., &
Collins, R. (1993). Posterior rotator cuff strengthening using
Theraband† in a functional diagonal pattern in collegiate
baseball pitchers. Journal of Athletic Training, 28, 346"354.
Schulthies, S.S., Ricard, M.D., Alexander, K.J., & Myrer, J.W
(1998). An electromyographic investigation of 4 elastic-tubing
closed kinetic chain exercises after anterior cruciate ligament
reconstruction. Journal of Athletic Training, 33(4), 328"335.
Sheppard, J., Hobson, S., Barker, M., Taylor, K., Chapman, D.,
McGuigan, M., et al. (2008). The effect of training with
accentuated eccentric load counter-movement jumps on
strength and power characteristics of high-performance volley-
9
ball players. International Journal of Sports Science & Coaching,
3(3), 355"363.
Simoneau, G.G., Bereda, S.M., Sobush, D.C., & Starsky, A.J.
(2001). Biomechanics of elastic resistance in therapeutic
exercise programs. Journal of Orthopedic and Sports Physical
Therapy, 31, 16"24.
Treiber, F.A., Lott, J., Duncan, J., Slavens, G., & Davis, H.
(1998). Effects of Theraband and lightweight dumbbell training on shoulder rotation torque and serve performance in
college tennis players. The American Journal of Sports Medicine,
26, 510"515.
Wallace, B.J., Winchester, J.B., & McGuigan, M.R. (2006).
Effects of elastic bands on force and power characteristics
during the back squat exercise. The Journal of Strength &
Conditioning Research, 20, 268"272.
Winter, D.A. (2004). Biomechanics and motor control of human
movement. Waterloo: Wiley InterScience.
Zatsiorsky, V.M. (2002). Kinematics of human motion. Champaign,
IL: Human Kinetics.