Kapoor & Agnihotri.: Effectiveness of isotonic and isokinetic trainings on quadriceps peak torque
Serb J Sports Sci 4(1): 17-22
Serbian Journal of Sports Sciences
ISSN 1820-6301
Original article
2010, 4(1): 17-22
ID 173771020
Received: 15 June 2009
Accepted: 15 Oct 2009
UDC 796.015.52 ; 796.012.11
THE COMPARATIVE EFFECTIVENESS
EFFECTIVENESS OF ISOTONIC
ISOTONIC AND ISOKINETIC
STRENGTH TRAININGS ON QUADRICEPS
QUADRICEPS PEAK TORQUE
Soniya Kapoor & Hitanshu Agnihotri
Maharishi Markandeshwar Institute of Physiotherapy & Rehabilitation, Maharishi Markandeshwar University,
Mullana, Ambala, INDIA.
Abstract The present study compares the effectiveness of isotonic and isokinetic exercises on peak torque of
the quadriceps in 45 healthy young males. The subjects were randomly assigned into 3 groups (n=15): Group
A-Isotonic group, Group B-Isokinetic group, Group C-Control group. Peak torque of the quadriceps at velocities
of 2200/sec and 1000/sec was tested twice with a gap of 4 weeks using isokinetic dynamometer. The isotonic
protocol included 3 sets of 10 repetitions at 50% 10 RM, 75% 10 RM and 100% 10 RM with a 1-minute rest
interval between the sets. The isokinetic protocol consisted of one set of 10 repetitions at velocities of 2200/sec,
1600/sec, 1000/sec, and 400/sec each with a 1-minute rest interval between the sets. Each exercise protocol was
performed thrice a week for 4 weeks. The subjects in the control group were not prescribed any kind of exercise
training. The comparison of peak torque values at 2200/sec (F=3.17, p>0.05) and 1000/sec (F=1.56, p>0.05) at
baseline with one way ANOVA showed statistically non-significant differences in all the groups. Post-test one
way ANOVA revealed significant differences at 2200/sec (F= 4.47, p<0.05) between and within the groups.
Isotonic exercises were found to be more effective than isokinetic exercises in increasing the peak torque at
high velocity.
Key words: Isotonic, isokinetic, peak torque, strength training, quadriceps
INTRODUCTION
The lack of force generation by the muscles is an impairment contributing to an inability to perform everyday
or sports activities. The musculature around the knee, especially the quadriceps, is important in the
prevention of injuries, as well as in the enhancement of the knee function. Isotonic and isokinetic exercises
are commonly used methods of developing quadriceps muscle strength in both sports medicine and
rehabilitation [7, 11, 16, 23].
During isotonic contractions, the neuromuscular system has to overcome an initial resistance
(constant throughout the movement) to move the lever arm [20]. On the other hand, isokinetic contractions
provide muscle training throughout the range of motion of the joint at a pre-set, constant speed of
contractions with a constantly accommodating resistance [25].
There is an ample volume of literature regarding the comparison of both isotonic as well as isokinetic
strength training programs on quadriceps muscle strength development. However, controversy still exists
regarding the use of these exercises for strength development. Several researchers have indicated isotonic
exercises to be more efficacious than isokinetic exercises for muscle training during rehabilitation [17, 21].
In contrast, Cordova et al. [9] and Wojtys et al. [24] reported isokinetic strength training to be at the upper
edge over isotonic training.
Indeed, there is a scarcity of evidence regarding the comparison of the effect of open chain and
specific training regimen types of isotonic and isokinetic exercise programs on the peak torque of the
quadriceps muscle. The relationship between joint torque and angular velocity is often used to quantify
dynamic strength, similar to the force-velocity relationship in isolated muscle [12]. The ability to perform a
dynamic task often depends on both torque production and the speed of contraction, the product of which is
power [23]. Therefore performance during dynamic muscle contractions can be examined by measuring
torque across a range of velocities.
Henceforth, the present study was undertaken to evaluate the comparative effectiveness of isotonic
and isokinetic strength training programs on quadriceps peak torque in order to find the most appropriate
method of developing muscle strength amongst healthy young males. Significant neurophysiological
17
Kapoor & Agnihotri.: Effectiveness of isotonic and isokinetic trainings on quadriceps peak torque
Serb J Sports Sci 4(1): 17-22
adaptations to resistance training occur in 4 weeks [15]. Henceforth, it was hypothesized that both strength
training methods will enhance the quadriceps peak torque after 4 weeks. As previous research has
documented both training methods to be superior to each other, we further hypothesized that either of the
two exercises may be better than the other.
MATHERIALS AND METHODS
METHODS
SAMPLES
AMPLES
Sixty healthy young males of 19-25 years of age were randomly taken from Maharishi Markendeshwar
University, Mullana. Out of the sixty, only fifty-one subjects met the inclusion criteria of having normal Body
Mass Index (BMI) value i.e. 18.5 - 24.9 Kg/m2. Out of these fifty-one subjects, six were removed as they
matched the exclusion criteria of either having history or evidence of lower extremity musculoskeletal or neurological
problems, cardio-vascular, respiratory or major systemic disorders, insufficient strength to complete base line testing
or participation in any type of vigorous or recreational activity, aerobic or weight training program during 6 months
prior to the study. The remaining forty-five male subjects were familiarized with the experimental protocol and
informed about the possible risks and benefits involved in the study both verbally and in writing before
giving written consent. The study was approved by Institutional Medical Ethics Committee.
INSTRUMENTATION
Easytech Genu 3 Isokinetic dynamometer, manufactured by Biomed-Inc., New Delhi was used for both
assessment of Peak torque (Newton-meter) and isokinetic strength training. Quadriceps strengthening
table, manufactured by Biomed-Inc, New Delhi was used for isotonic strength training. A static lower limb
bicycle ergometer was used for warm-up prior to each assessment and training session. A weighing
machine and an anthropometric rod were used to measure body weight and height, respectively.
TESTING PROTOCOL
Forty-five subjects were randomly assigned into 3 groups of 15 subjects each (n=15): Group A - Isotonic
group, Group B - Isokinetic group, Group C – No exercise Control group. All the subjects of the three
groups were pre-tested and post-tested with a gap of four weeks using isokinetic dynamometer to evaluate
peak torque of the quadriceps. The subjects were asked to perform 10 repetitions at 2200/sec followed by
10 repetitions at 1000/sec with a rest interval of 1 minute between the sets. The peak torque of the
quadriceps at both velocities was recorded. A general body warm-up of 5-minute easy stationary cycling
followed by a 5-minute rest interval was included before each testing.
TRAINING PROTOCOL
Group A (Isotonic group):
Each subject was asked to do general body warm-up of 5-minute easy stationary cycling followed by a 5minute rest interval before each exercise session. 1RM was estimated using Brzyncki [6] equation:
•
1RM = Weight lifted during n RM / (1.0278 - 0.0278(n))
10 RM was determined through 75% of the 1 RM [15]. Each exercise session consisted of three sets of 10
repetitions and 1-minute rest between the sets. Each exercise session was performed three times a week
for four weeks.
Isotonic protocol• 10 repetitions with 50% 10 RM
• 10 repetitions with 75% 10 RM
• 10 repetitions with 100% 10 RM
Group B (Isokinetic group):
Subjects were asked to do general body warm-up of 5-minute easy stationary cycling followed by a 5minute rest interval before exercise.
Isokinetic protocol• Speed (Deg/sec)
220 160 100
• Reps
10
10
10
• Sets
1
1
1
• Rest - 1 minute between the sets
• Duration - 3 days a week for 4 weeks
18
40
10
1
Kapoor & Agnihotri.: Effectiveness of isotonic and isokinetic trainings on quadriceps peak torque
Serb J Sports Sci 4(1): 17-22
Group C (Control group):
The subjects in the control group were tested twice with the gap of 4 weeks.
STATISTICAL ANALYSIS
All data are presented as the mean ± standard deviation (SD). The data were analyzed for statistical
significance by using the statistical package for social sciences (SPSS 16.0) software. Two way ANOVA
followed by post hoc multiple Scheffe analysis was done.
RESULTS
The Mean ± Standard Deviation (SD) values for Group A, Group B, Group C at Pre and Post testing at
2200/sec and 1000/sec are shown in Table 1, Table 2, and Table 3, respectively. The comparison of peak
torque values at 2200/sec (F=3.17, p>0.05) and 1000/sec (F=1.56, p>0.05) at baseline with one way ANOVA
showed statistically non significant differences in all the groups. One way ANOVA revealed statistically
significant changes only at 2200/sec (F= 4.47, p<0.05) (Table 4). Post hoc multiple Scheffe analysis showed
peak torque of isotonic group to be higher than in the isokinetic group. The control group showed least peak
torque values.
0
0
Table 1. Intra group comparison for peak torque at 220 /sec and 100 /sec for Group A (Isotonic group).
0
220 /sec
0
220 /sec
0
100 /sec
0
100 /sec
VariablePeak Torque
Peak Torque Pre
Peak Torque Post
Peak Torque Pre
Peak Torque Post
Mean
(Newton meter)
90.80
135.53
142.40
183.60
** = Highly significant (p< 0.001) * = Significant (p<0.05)
ns
Std
Deviation
44.11
55.49
63.54
51.79
Mean ∆ %
differences
t value
49.26
4.62
28.93
2.49
**
*
= Non-significant (p>0.05)
0
0
Table 2. Intra group comparison for peak torque at 220 /sec and 100 /sec for Group B (Isokinetic group).
0
220 /sec
0
220 /sec
0
100 /sec
0
100 /sec
VariablePeak Torque
Peak Torque Pre
Peak Torque Post
Peak Torque Pre
Peak Torque Post
Mean
(Newton meter)
109.53
125.20
173.13
206.53
** = Highly significant (p< 0.001) * = Significant (p<0.05)
ns
Std
Deviation
34.50
45.71
40.70
71.38
Mean ∆ %
differences
t value
14.31
3.42
19.25
1.80ns
*
= Non-significant (p>0.05)
0
0
Table 3. Intra group comparison for peak torque at 220 /sec and 100 /sec for Group C (Isokinetic group).
0
220 /sec
0
220 /sec
0
100 /sec
0
100 /sec
VariablePeak Torque
Peak Torque Pre
Peak Torque Post
Peak Torque Pre
Peak Torque Post
Mean
(Newton meter)
76.87
88.67
172.27
183.60
** = Highly significant (p< 0.001) * = Significant (p<0.05)
ns
Std
Deviation
26.12
30.64
58.62
52.59
Mean ∆ %
differences
t value
15.35
2.02ns
6.58
0.82ns
= Non-significant (p>0.05)
Table 4. Post test ANOVA between and within groups.
Peak
torque
220
Peak
torque
100
Between Groups
Within Groups
Total
Between Groups
Within Groups
Total
Sum of
Squares
18189.73
85513.47
103703.20
9608.93
159416.27
169025.20
** = Highly significant (p< 0.001) * = Significant (p<0.05)
df
2
42
44
2
42
44
ns
Mean
Square
9094.87
2036.04
F value
4804.47
3795.63
4.47
1.26
**
ns
= Non-significant (p>0.05)
19
Kapoor & Agnihotri.: Effectiveness of isotonic and isokinetic trainings on quadriceps peak torque
Serb J Sports Sci 4(1): 17-22
220 deg/s
140
135.53
130
125.2
Peak Torque (Nm)
120
109.53
110
100
90
90.8
88.67
A group
B group
C group
80
70
76.87
60
0 w eek
4th w eek
Training Duration
Figure 1. Intra group comparison of peak torque (Nm) at 220 deg/sec for group A, B and C.
110 deg/s
220
210
206.53
Peak Torque (Nm)
200
190
180
183.6
173.13
183.6
170
160
172.27
150
140
A group
B group
C group
142.4
130
120
0 week
4th week
Training Duration
Figure 2. Intra group comparison of peak torque (Nm) at 110 deg/sec for group A, B and C.
DISCUSSION
The findings from the present study suggest that both Isotonic (at 2200/sec and 1000/sec) and Isokinetic (at
2200/sec) strength training programs improved the peak torque of the quadriceps after 4 weeks. On the other
hand, non-experimental control group did not yield any significant changes in the intra-group comparison.
As previously stated, there have been decades of compiling a substantial database relevant to the
effects of both types of strength trainings on various muscle groups throughout the body [1, 4, 5, 18, 19].
Although both isotonic and isokinetic contractions present different biomechanical characteristics, they both
load the neuromuscular system [22]. An increase in the number and frequency of firing motor units has
been observed after isotonic and isokinetic strength training [21]. Remaund et al. [20] suggested that
specific changes on the torque-angle and torque-velocity relationship may be induced with both isotonic and
isokinetic strength training.
Furthermore, the isotonic group revealed the highest peak torque value on post-training at 2200/sec,
followed by the isokinetic and control groups respectively. Besides Kovaleski et al. [17] and Schmitz and
Westwood [21], similar results have also been reported by Smith and Melton [22]. There may be many underlying
factors responsible for such findings. Greater motor unit activation per unit of work performed with isotonic
exercise as compared to isokinetic exercises may be one of the reasons for better improvement with
isotonic strength training as observed by Schmitz and Westwood [21]. Kovaleski et al. [17] also found
20
Kapoor & Agnihotri.: Effectiveness of isotonic and isokinetic trainings on quadriceps peak torque
Serb J Sports Sci 4(1): 17-22
greater strength improvement with isotonic training than with isokinetic training on isometric tests at 100,
300, 500, 700 and 900 of knee flexion. They reported similar findings for isotonic and isokinetic power.
According to Connelly and Vandervoot [8], isotonic exercises are the closest form of exercise to
normal movement, that is, they are close to functional movement. So, it would not be surprising to find that
these exercises increase muscle strength at double the speed of isometric and isokinetic exercises in the
untrained population.
Another important explanation for lower peak torque values following isokinetic strength training may
be that it provides constantly accommodating resistance rather than maximal resistance during the exercise
because the resistance provided by the isokinetic dynamometer matches the force exerted on the
attachment arm by the user through the range of motion of an exercise [10]. Hostler [13] has reported that
optimal strength development can occur only when a muscle contracts against a degree of resistance high
enough to reach a maximal or near maximal effort, which is enough to cause fatigue to the trained muscle.
Moreover, isokinetic exercise involves three phases of movement; acceleration, constant velocity,
and deceleration. The acceleration phase, the rate of velocity development, represents the beginning part of
the motion and is performed without resistance. The constant velocity phase follows the acceleration phase
of movement and corresponds to the match between mechanically imposed velocity and the subject’s
movement. The third phase of motion, the deceleration phase, represents slowing down of the device prior
to contacting the end stop [3]. By definition, only the constant velocity portion of the range of motion
represents load range [4]. Thus, maximal loading of the neuromuscular system may occur only during the
second phase of the isokinetic exercise.
Another important factor is co-activation of the hamstring muscle during isokinetic knee extension
which may have led to weaker work:repetition ratio with isokinetic strength training. Co-activation of the
hamstring muscle during isokinetic knee extension exercises has been reported by many researchers in the
past [2, 14, 20].
CONCLUSIONS AND PRACTI
PRACTICAL
TICAL APPLICATION
The findings of this study can be summarized as follows: both isotonic and isokinetic exercises are effective
in increasing the quadriceps muscle strength. However, isotonic exercises are more effective than the
isokinetic exercises in increasing the peak torque at high velocity i.e. 2200/sec. Thus, considering the above
findings, isotonic strength training should be used in order to enhance strength indices and possibly in
competition results in sprint and power sports requiring more quadriceps strength. Future studies need to
focus on other factors such as different velocities, repetitions, duration of training, as well as examining the
interaction of fatigue and velocity spectrum training on larger sample sizes. Since it is an easily
understandable and applicable method, we recommend health professionals to add open chain isotonic
training in rehabilitation program following injury.
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Address for correspondence:
Hitanshu Agnihotri,
House Number-339,
Sector - 41 A,
Chandigarh-160036, India
Tel.: 91-172-2628249; 91-9417913358
E-mail: [email protected]
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