Isokinetic Strength Training
Program for Muscular Imbalances in Professional Soccer Players
A.
Gioftsidou
1,
I. Ispirlidis 2,
G. Pafis 1,
P. Malliou 1,
Ch. Bikos 3,
G. Godolias1
1Department
of Physical Education and Sports Science, Democritus University of
Thrace, Komotini, Greece
2
Skoda Xanthi FC, Xanthi, Greece
3
Orthopedic
Department, General Hospital of Xanthi, Xanthi, Greece
Address correspondence to
|
Dr. Asimenia Gioftsidou,
|
|
Department of Physical
Education and Sports Science,
|
|
Democritus University of
Thrace,
|
|
Campus
|
|
69100 Komotini, Greece
|
|
tel : +302531039662
fax : +302531039623
|
|
e-mail (agioftsi@phyed.duth.gr).
|
ABSTRACT
The aim of the
study was to investigate the effect of a
muscular training program on soccer players` performance of which
initially appeared imbalanced or bilaterally asymmetrical. The
study was conducted on 68 professional soccer players (age: 24,1
± 5,7
yr,
weight: 76,8 ± 5,7
kg, height: 1,82 ±
0,7 cm) participating in the championship of the
1st
Greek division (2 years study). During the preparation period,
all the players performed an isokinetic measurement of knee flexors
and extensors (60sec-1
and 180sec-1).
These initial measurements detected muscular imbalances or deficits
in 15 players the 1st year, and in 12 players the 2nd
year. The 27 players followed a specific isokinetic training program
for 2 months, 3 times per week. After the
completion of the isokinetic training program, the 68 players
underwent the same isokinetic test. The analysis revealed
significant differences between the pre- and post-training measures
at both angular velocities in peak torque values, in differences from
one limb to the other, and in peak torque ratios for flexors and
extensors. Consequently, the application of this specific isokinetic
training program can restore imbalances in knee muscle strength
efficiently.
Key
words: soccer,
isokinetic training program,
muscle
imbalances, knee flexors and extensors
|
Soccer
is one of the most popular sports and attracts many participants all
over the world (Heidt,
Sweeterman, Carlona, Traub, Tekulve 2000; Peterson, Chomiak,
Graf-Baumann, Dvorak 2000; Soderman, Werner, Pietila, Engstrom,
Alfredson 2000).
This participation though, leads to a considerable number of
musculoskeletal injuries (Inklaar,
Bol, Schmikli, Mosterd1996; Dvorak 2000).
Some
of the factors responsible for soccer injuries are, contact with an
opponent, field conditions, or are training related, e.g.,
muscle-strength imbalances or deficits (Inklaar
1994; Heidt, Sweeterman, Carlona, Traub, Tekulve 2000).
Sahrmann (1989)
and, similarly, Caillet (1977)
define muscle imbalance as a failure of the agonist-antagonist
relationship. The terms balance or imbalance do not refer to equal
or unequal torque values, but to the balance between the torque
ratios of agonistic and antagonistic muscle groups. Practitioners
have often used ipsilateral agonist/antagonist muscle ratios as
standards by which to measure the progress of rehabilitation or to
assess muscle imbalance (Brown
2000).
Concentric hamstring-to-quadriceps torque ratios have been studied
extensively (Perrin
1993)
with reported averages ranging from 0.5 to 0.75.
Similarly,
many researchers report that bilateral differences (>15%) in
muscular performance (quadriceps and hamsting) detected with
isokinetic measures have been also considered as an important
predictor of soccer players´ injuries or a result of previous
injury due
to an incomplete rehabilitation program (Brown
2000; Leatt, Shephard, Plyley 1987; Croiser, Crielaard 2000).
Since soccer frequently involves one-sided activities such as kicking
only with one leg, asymmetries in muscle strength between the two
legs are possible (Leatt,
Shephard, Plyley 1987; Kellis, Gerodimos, Kellis, Manou 2001).
However, it is also possible that weaknesses
or muscle imbalances identified by isokinetic testing, are almost
always associated with a current or previous injury (Wrigley
2000).
The
first aim of the present study was to detect the possible imbalances
in muscular strength in soccer players. The second aim was to
investigate the effect of a specific muscle-training program to
restore the normal torque ratios of hamstring and quadriceps,
reducing bilateral differences.
Methods
Sample
The
study was conducted on 68 professional players (age: 24,1 ±
5,7
yr, weight: 76,8 ±
5,7 kg,
height: 1,82 ±
0,7
cm) who played in the first Greek National
division
(two years study). The
1st
year of the study 12
of
the
35 players
and the 2nd
year
11 from the 33 players were added to this team at
the
beginning
of
the
preparation
period.
All
the
players
were
healthy
without
obvious symptoms or pain during soccer training.
Procedure
During the preparation period, the 68 players (35
the 1st
year and 33 the 2nd
year) accomplished an isokinetic test of knee
flexor and extensor muscle groups (pre-training measure), to detect
possible imbalances or bilateral differences in muscular strength. A
Cybex Norm (Lumex Corporation, Ronkohoma, NY) dynamometer was used
for the isokinetic measurement. Procedures were in accordance with
ethical standards of the Committee on Human Experimentation at the
Institution at which the work was conducted and with the Helsinki
Declaration of 1975.
Prior to undergoing
the testing procedure, each subject performed a 10 min warm-up of
cycling and a 5 min warm up of stretching exercises. The test was
performed in a seated position (hip flexion =110).
A random specifying of
starting limb was followed to minimize the effects of learning bias.
Three submaximal and one maximal repetition of the trial at each
speed were performed before each session to prepare the subject for
the testing procedure. Testing was performed at low and moderately
high angular velocities, 60°
sec-1
and 180°
sec-1.
These angular velocities have been used by many investigators in
order to evaluate knee muscular strength of soccer players (Kellis,
Gerodimos, Kellis, Manou 2001; Dauty, Poriton-Josse, Rochcongar 2003;
Ergun, Islegen, Taskiran 2004).
A 30 sec rest was allowed between tests for all subjects (between the
two angular velocities). Following the testing of one leg, there was
a 3 minute rest and then the testing of the other leg began.
Data were recorded
during three maximal repetitions of extension and flexion movements
at each speed. The best peak torque value for each angular velocity
defined the muscular strength.
These initial
measurements detected muscular imbalances or deficits in 15 soccer
players the 1st
year, and in 12 players the 2nd
year. These
27 players gave an interview to the rehabilitation trainer of the
team about their previous injuries because most of them just had been
placed on the team.
The 27
players
followed a specific isokinetic training program for 2 months with a
frequency of 3 times per week to correct the imbalances and deficits.
The
isokinetic training program included 10 sets (velocity spectrum
exercise). The first 5 sets were executed with maximal effort in both
flexor and extensor muscle groups, while the last 5 sets were
executed maximally only for the weak muscle group based on the
initial measurement (Table
1).
Table
1.
The isokinetic training program
Angular Velocity
|
Set
|
Repetitions
|
Muscle group
|
150° sec-1
|
1
|
15
|
Extensors and flexors
|
180° sec-1
|
1
|
15
|
Extensors and flexors
|
210° sec-1
|
1
|
15
|
Extensors and flexors
|
240° sec-1
|
2
|
15
|
Extensors and flexors
|
240° sec-1
|
2
|
15
|
Extensors or flexors
|
210° sec-1
|
1
|
15
|
Extensors or flexors
|
180° sec-1
|
1
|
15
|
Extensors or flexors
|
150° sec-1
|
1
|
15
|
Extensors or flexors
|
After
the completion of the isokinetic training program the 27
involved players and the other 41 healthy soccer players
of the team underwent the same isokinetic test (post-training
measure).
Analysis
Data
were analyzed using the SPSS PC (Version 8.0) program for Windows.
Repeated-measures analysis of variance was used to test differences
between pre- and post-training measures. Statistical significance was
set at p<.05.
Results
According
to the pre-training assessments, in 27 of 68 soccer players muscular
imbalances or deficits were discovered. Differences between strengths
of muscles on different sides of the body were 24% (SD=1)
for the knee extensors and 18% (SD=11)
for the knee flexors at the angular velocity of 60°
sec-1.
At the angular velocity of 180°
sec-1
the
differences were 23% (SD=12)
for the knee extensors and 20% (SD=13)
for the knee flexors. Differences in flexor to extensor strength
ratios were also found between agonist and antagonist muscle groups.
In 60° sec-1
angular
velocity, the ratio was 52% (SD=21)
for the right leg and 51% (SD=22)
for the left leg, and at 180° sec-1
was 57% (SD=18)
for the right leg and 59% (SD=20)
for the left leg.
These
27
players were interviewed by the rehabilitation trainer about any
injuries suffered during the last 3 years. Descriptive
statistics showed that 13 players had hamstring
strains (13/27), 9 had knee ligament strains (5 Anterior Cruciate
Ligament and 4 Medial Collateral Ligament) (9/27), 3 had anterior
knee pain (3/27) and 2 had an adductor strain (2/27).
Regarding
the effectiveness of the training program applied to the 27 players
(training group),
repeated
measures analysis of variance showed significant differences between
pre and post training measures only for the training group.
More specifically, the training group appeared to improve in
peak torque values;
for
right knee extensors at the angular velocity of 60°
sec-1
F(1,26)=424,6
p<.05,
and 180°
sec-1
F(1,26)=317,8
p<.05
and for right knee flexors at the angular velocity of 60°
sec-1
F(1,26)=411,23
p<.05,
and 180°
sec-1
F(1,26)=319,22
p<.05
(Table
2).
Similarly
results revealed for the for left knee extensors at the angular
velocity of 60°
sec-1
F(1,26)=431,5
p<.05,
and 180°
sec-1
F(1,26)=339,42
p<.05
and for left knee flexors at the angular velocity of 60°
sec-1
F(1,26)=411,13
p<.05,
and 180°
sec-1
F(1,26)=335,45
p<.05
(Table
2).
Table
2.
Means and standard deviations of
knee extensors´ and flexors´
peak torque for the right and left legs
Angular
Velocity |
|
|
60° sec-1 |
180° sec-1 |
|
|
Right Leg |
Left Leg
|
Right Leg |
Left Leg |
Knee Extensor Strength (Nm)
|
|
|
|
|
|
Healthy Group |
|
|
|
|
|
Pre-training |
Μ |
244.7 |
243.1 |
161.4 |
160.9 |
|
SD |
25.3 |
25.9 |
21.2 |
19.8 |
Post-training |
Μ |
245.8 |
242.7 |
163.1 |
161.7 |
|
SD |
25.3 |
24.1 |
20.2 |
18.9 |
Training Group |
|
|
|
|
|
Pre-training |
Μ |
232.6a |
231.8a
|
156.3a |
154.2a |
|
SD |
31.2 |
31.9 |
25.3 |
22.8 |
Post-training |
Μ |
246.6 a |
243.3a
|
163.6
a |
162.6 a |
|
SD |
21.5 |
16.8 |
13.5 |
16.3 |
Knee Flexor Strength
(Nm) |
|
|
|
|
|
Healthy Group |
|
|
|
|
|
Pre-training |
Μ |
166.1 |
166.5 |
123.2 |
123.6 |
|
SD |
20.3 |
21.6 |
18.3 |
16.5 |
Post-training |
Μ |
167.8
|
169.6 |
126.1 |
125.9 |
|
SD |
18.4 |
19.6 |
16.8 |
16.3 |
Training Group |
|
|
|
|
|
Pre-training |
Μ |
154.9b
|
156.5 b
|
112.7 b |
111.4 b |
|
SD |
26.1
|
27.1 |
19.2 |
18.4 |
Post-training |
Μ |
169.8 b
|
170.7 b
|
129.4
b |
126.8
b |
|
SD |
19.4
|
19.2 |
15.2 |
15.7 |
ab p<.05
In
addition, significant differences in peak torque ratios of flexors to
extensors were found between the pre- and post-training measurements.
At 60°
sec-1
angular velocity, the ratio changed from 0.52 (±21)
to 0.66 (±8)
for the right leg, and from 0.51 (±22)
to 0.65 (±8)
for the left leg. Respectively, at the 180°
sec-1
angular velocity, the ratio changed from 0.57 (±18)
to 0.67 (±7)
for the right leg, and from 0.59 (±20)
to 0.67 (±9)
for the left leg.
For the training
group, at the post training measures the bilateral differences
decreasing significantly (Table 3).
Table
3.
Pre- and Post-training Bilateral Differences in Muscle Strength
Angular velocity |
Bilateral Differences (%) |
°sec-1
|
Knee Extensors |
Knee Flexors |
|
Pre-training |
Post-training |
Pre-training |
Post-training |
|
M |
SD |
M |
SD |
M |
SD |
M |
SD |
60°sec-1
|
24 |
15 |
10** |
5 |
15 |
7 |
7** |
7 |
180°sec-1
|
18 |
12 |
8** |
6 |
17 |
5 |
4** |
4 |
**
p<. 01 significant statistical difference between pre and post
training measures
Finally,
at the post-training measures there were not significant differences
(p>.05) between the training group (27 players) and the rest
healthy soccer players (41 players) in peak torque values for knee
extensors and flexors at both angular velocities (Table 2).
Discussion
Some
coaches, athletes, medical personnel, strength and conditioning
staff, believe that injury is often the result of weaknesses in
particular muscle groups, which can be detected by isokinetic testing
(Wrigley
2000).
However, it is still more important that, weaknesses identified by
isokinetic testing, are almost always associated with a current or
previous injury (Wrigley
2000).
More specifically, Schwellnus
(2004) reported that many factors are postulated to increase the
risk of developing acute muscle injuries, such as previous recent
muscle injury (Orchard 2001; Emery, Meeuwisse 2001; McHugh
2004) and past muscle injury (Orchard 2001; McHugh
2004).
Hagglund,
Walden and Ekstrand (2005),
reported that in Denmark and Sweden 30% and 24% of the injuries in
soccer were re-injuries. This is within the range of what has been
reported from most studies, where 22-42% were re-injuries (Nielsen,
Yde 1989; Engstrom, Forssblad, Johansson, Tornkvist1990; Hawkins,
Fuller 1996). Inadequate rehabilitation and premature return to play
after injury have been suggested as risk factors for recurrence of
injury in previous studies (Hagglund, Walden, Ekstrand, 2005).
In
addition, Schwellnus
(2004) reported and some other factors who increase the risk of
developing acute muscle injuries, such as decreased muscle strength
(mainly eccentric muscle strength) (Askling, Karlsson, Thorstensson
2003), and muscle imbalance (decreased eccentric (antagonist) to
concentric (agonist) muscle strength) (Dauty, Poriton-Josse,
Rochcongar 2003).
The
most effective interventions to reduce the incidence of muscle
injuries will be those that address known risk factors
(McHugh
2004). The best approach is to identify risk factors for the
population of interest and then develop interventions specifically
for that population. In practice, most teams are interested in
applying an intervention without first studying the injury patterns
and risk factors in their own athletes. In this situation, one of the
most obvious risk factors to address is a history of a previous injury
(Emery, Meeuwisse 2001; McHugh
2004).
The high rate of recurrence for muscle injuries indicates incomplete
recovery and may be attributable to inadequate rehabilitation.
Therefore athletes with a history of previous injuries could be
placed on a rehabilitation programme to address the involved muscle
group (McHugh
2004).
The
isokinetic measurement performed in the present study detected many
muscle strength imbalances (concentric
hamstring-to-quadriceps ratio lower than 0.6)
(Heiser,
Weber, Sullivan, Clare, Jacobs 2002),
and
deficits (bilateral
differences >15%)
(Leatt,
Shephard, Plyley 1987; Croiser, Crielaard 2000; Wrigley 2000).
More
specifically,
in two years, 27 of 68 soccer players on this team appeared to have
deficits and/or imbalances in the knee joint muscles, also
due to an incomplete rehabilitation program after knee injuries. In
accordance with the present study statement is a study performed on
sprint runners. Jonhagen and his coworkers (Johnagen,
Nemeth, Eriksson 1994)
found that sprint runners with a history of very severe hamstring
strains were weaker than the uninjured sprinters. Similarly, Ekstrand
and Gillquist (1983)
studied 180 senior amateur soccer players and mentioned that
non-contact knee injuries occurred in knees with pathological
ligamentous laxity due to previous knee injuries.
The 27 soccer players
followed the specific isokinetic training program for 2 months with a
frequency of 3 times per week in order to correct the imbalances and
the deficits. As regards the isokinetic training program, it used
a method of strength training appropriate to
promote an optimal neuromuscular response, a velocity spectrum
exercise protocol included 10 sets (Kovaleski,
Heitman 2000).
The
first 5 sets were executed with maximal effort in both flexor and
extensor muscle groups, in order to improve the muscle strength,
while the last 5 sets were executed maximally only for the weak
muscle group (as determined by the initial measurement), in order to
correct the muscle imbalances and deficits (Table 1).
The results showed
that there were significant differences between the pre- and
post-training measures in peak torque values for knee extensors and
flexors at both angular velocities. In addition, it is important that
these players not only increase their peak torque values but also
decrease the variability (standard
deviations) of
strength measures. Moreover, at the post-training measures there
were no significant differences (p>.05) between the training
group (27 players) and the healthy soccer players (41 players)
in peak torque values for knee extensors and flexors at both angular
velocities.
Examining the effectiveness of the training program in
correcting strength deficits and/or imbalances, the results showed
that a specific isokinetic training program, performed for 2 months
with a frequency of 3 times per week, can restore efficiently the
muscular performance expressed by peak torque (Table 2). Thus, the
application of an isokinetic test is useful in examination of
possible muscle strength imbalances or bilateral differences in
strength of knee muscle groups, and the performance of a specific
isokinetic training program could eliminate these strength deficits
and/or imbalances.
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