Effects of an Electrostimulation Training Program on Strength, Jumping, and Kicking Capacities in Soccer Players

Abstract

The present study investigated the influence of a 5-week electrostimulation (EMS) training program on muscular strength, kicking velocity, sprint, and vertical jump performance in soccer players. Twenty amateur soccer players participated in the study, 10 in the electrostimulated group and the remaining 10 in a control group. Electrostimulation was applied on the quadriceps muscles over 5 weeks. Subjects were tested before, during (wk-3), and after (wk-5) the EMS training program. Maximal voluntary contraction using different contraction mode (i.e., eccentric, concentric, and isometric), vertical jump height, sprint running for 10 m, and ball speed were examined. We observed an increase in isometric and eccentric maximal knee extension torques and also a gain in ball speed performance without run up at wk-3. After 5 weeks of EMS training, eccentric, isometric, and concentric torques and ball speed had significantly improved. It appeared appropriate to conduct EMS training during at least 3 weeks to observe beneficial effects in specific soccer skills such as ball speed.

Full text

EFFECTS OF AN ELECTROSTIMULATION TRAINING
PROGRAM ON STRENGTH,JUMPING,AND KICKING
CAPACITIES IN SOCCER PLAYERS
MAXIME BILLOT,
1
ALAIN MARTIN,
1
CHRISTOS PAIZIS,
1,2
CAROLE COMETTI,
2
AND NICOLAS BABAULT
2
1
Laboratory INSERM U887 Motricity-Plasticity, Faculty of Sport Science, University of Burgundy, Dijon, France; and
2
Performance Expertise Center, Faculty of Sport Science, University of Burgundy, Dijon, France
ABSTRACT
Billot, M, Martin, A, Paizis, C, Cometti, C, and Babault, N.
Effects of an electrostimulation training program on strength,
jumping, and kicking capacities in soccer players. J Strength
Cond Res 24(5): 1407–1413, 2010—The present study investi-
gated the influence of a 5-week electrostimulation (EMS) train-
ing program on muscular strength, kicking velocity, sprint, and
vertical jump performance in soccer players. Twenty amateur
soccer players participated in the study, 10 in the electro-
stimulated group and the remaining 10 in a control group.
Electrostimulation was applied on the quadriceps muscles over
5 weeks. Subjects were tested before, during (wk-3), and after
(wk-5) the EMS training program. Maximal voluntary contraction
using different contraction mode (i.e., eccentric, concentric,
and isometric), vertical jump height, sprint running for 10 m, and
ball speed were examined. We observed an increase in
isometric and eccentric maximal knee extension torques and
also a gain in ball speed performance without run up at wk-3.
After 5 weeks of EMS training, eccentric, isometric, and
concentric torques and ball speed had significantly improved. It
appeared appropriate to conduct EMS training during at least 3
weeks to observe beneficial effects in specific soccer skills
such as ball speed.
KEY WORDS ball speed, knee extensors, isokinetic dynamometer,
isometric and eccentric strength
INTRODUCTION
Soccer necessitates explosive-type efforts such as
tackling, jumping, kicking, and sprinting (32). It has
previously been demonstrated that 10-m sprint
performance was higher in elite than in amateur
soccer players (4,9), and it is generally accepted that muscles
of the thigh play an important role in running (35), jumping,
and ball kicking (2,14,30). Some studies, such as that of Narici
et al. (27), demonstrated a positive correlation between
quadriceps maximal voluntary contraction (MVC) and maxi-
mal ball velocity. Furthermore, Wisloff et al. (35) reported
a positive correlation between maximal squat strength,
sprinting, and jumping in elite soccer players. A correlation
has also been observed between sprinting and jumping abilities
and torque at concentric velocities normalized to subjects’
body mass (10). Quadriceps muscles seem important for
soccer players. Training of these specific muscles could
therefore induce positive modifications in soccer performance.
It has been reported that a 12-week (4 days a week)
voluntary isometric training program induced a significant
increase in squat jump (SJ)–height performance in young
adults (20). In the specific case of soccer, previous studies
have found that voluntary strength training improved
performance in a specific kicking ball task in soccer (8,11).
Therefore, voluntary strength training induces benefits in
specific soccer abilities. Among the different training
methods, the electrostimulation (EMS) method could
improve muscle strength production (5,12,13,21). Indeed,
enhancement in strength production was evident in many
muscular groups after EMS training ranging from 10 to 41%
for quadriceps muscles (3,7,15,16,23,25). Some authors have
tested the effects of EMS training on sport performance.
After 4 weeks of EMS training on quadriceps and triceps
surae muscles, Malatesta et al. (23) reported the positive
effects on vertical jump performance in volleyball players.
Furthermore, Maffiuletti et al. (23) found that SJ performance
in basketball players was improved by 14% after 4 weeks of
EMS training on quadriceps muscles. Similarly, it was
reported that 3 weeks of EMS on latissimus dorsi and
quadriceps muscles decreased stroke and sliding sprint time
in swimming and ice hockey, respectively (7,31). On the
other hand, Babault et al. (3) measured an increment in squat
performance after 6 and 12 weeks of quadriceps EMS
training, but observed no significant change on specific
scrumming tasks in rugby players.
It thus appeared that EMS training may enhance specific
sports movements such as stroke and sliding sprint (3,7,23–25,31),
Address correspondence to Maxime Billot, maxime.billot@u-bourgogne.fr.
24(5)/1407–1413
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Ó2010 National Strength and Conditioning Association
VOLUME 24 | NUMBER 5 | MAY 2010 | 1407

whereas improvements in others, such as jump height and
sprint time, remain unclear in the literature. To date, no study
has investigated the evolution of specific performance in
soccer after an EMS training program. Indeed, analysis of the
physiological profile of soccer players reveals the importance
of anaerobic power in most decisive skills such as jump,
sprint, and ball-kicking ability (4). It was also reported that
quadriceps femoris muscles are important for specific soccer
abilities. Thus, the aim of this study was to test the effects of
a 5-week EMS training program on the quadriceps femoris of
soccer players. With this intention, strength was measured in
different contractile conditions (i.e., isometric, concentric,
and eccentric). Moreover, special interest was given to the
evaluation of specific soccer tasks such as vertical jump,
sprint, and ball speed during kicking. We hypothesized
that a 5-week EMS training program on the quadriceps
femoris improved muscle strength and sport performance in
soccer players.
METHODS
Experimental Approach to the Problem
This study was designed to determine the beneficial effects of
a 5- weeks EMS training program in soccer players. Strength
adaptations were investigated by measuring the isokinetic
torque during maximal voluntary eccentric, isometric, and
concentric knee extensions. Sport performance adaptations
were investigated using ball speed after kicking, vertical
jumps, and sprinting. These variables were tested before, 3
weeks (wk-3) and 5 weeks (wk-5) after the beginning of
training. Two groups of soccer players were considered.
During the 5-week period, the first group (control, C) only
followed soccer trainings. The second group (electrostimu-
lated, EMS), in addition to the same soccer training,
underwent a 5-week EMS training on the knee extensors.
During the 5 weeks, the EMS training program consisted of 3
sessions a week. Statistical analyses allowed us to evaluate the
effect of EMS training on physical performances of soccer
players. Independent variables
were time (before, wk-3, and
wk-5) and groups (EMS and C).
Values obtained for the different
tests were used as dependent
variables.
Subjects
Twenty male soccer players
from the faculty of sport science
competing at least in the re-
gional division of the French
Football Federation voluntarily
participated in this study. They
were randomly assigned to an
electrostimulated group (EMS,
n= 10; age 20.1 62.1 years;
height 1.76 60.06 m; mass
69.5 67.4 kg) or control group
(C, n= 10; age 21.7 63.4 years;
height 1.80 60.05 m; mass
70.7 611.0 kg). All players
technically trained twice a week
(without physical training) and
competed once a week for a
total of practical soccer averag-
ing 5 hours a week. They were
asked to maintain their usual
training, food intake, and hy-
dration. The experiment was
conducted during March, cor-
responding to the last part of
the championship. None of
them had previously engaged
in systematic strength or EMS
training. Written informed con-
sent was obtained. All
Figure 1. Torque-angular velocity of knee extensors in electrostimulation group and control group. Values
measured before and after wk-3 and wk-5 are means 6SD. *,**, and ***Significant differences at p,0.05,
p,0.01, and p,0.001, respectively.
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experimental procedures conformed to the standards set by
the Declaration of Helsinki and were approved by the local
Committee on Human Research.
Procedures
The EMS group participated in a 5-week training program
that consisted of 12-minute EMS sessions, at a rate of 3
sessions per week. Electrostimulation was performed on both
quadriceps femoris muscles. During the stimulation, subjects
were seated on a machine used for strength quadriceps
strength training (Multi-form, La Roque D’anthe
´ron, France)
with the knee fixed at a 60°angle (0°corresponding to the full
extension of the leg). A portable battery-powered stimulator
(Compex-Energy, Medicompex SA, Ecublens, Switzerland)
was used. Three 2-mm-thick self-adhesive electrodes were
placed over each thigh. The positive electrodes, measuring 25
cm
2
(5 cm 35 cm), which had membrane-depolarizing
properties, were placed as close as possible to motor points of
vastus medialis and vastus lateralis muscles. Negative
electrodes, measuring 50 cm
2
(10 cm 35 cm), were placed
near the proximal insertion of rectus femoris muscle.
Rectangular wave pulsed currents (100 Hz) lasting 400 ms
were used. Electrical stimulation was 3-second long and was
followed by a rest period of 17-second (duty cycle 15%). This
program was adapted from Compex commercially strength
programs. During the training sessions, 36 contractions were
performed. Stimulation intensity was determined by the pain
tolerance of the subject. The maximally tolerated intensity
varied between 60 and 120 mA. The level of force produced
by EMS was measured with a myostatic type dynamometer
(Allegro, Sallanches, France),
and it was verified by the
examiner to produce a force
higher than 60% of MVC
during each training session.
For both EMS and C groups,
similar soccer training was
conducted twice a week.
Testing
Strength Tests. Tests were per-
formed before and after
a 3-week (wk-3) and 5-week
(wk-5) period. We used an
isokinetic dynamometer (Bio-
dex Corporation, Shirley, NY,
USA) to test the strength of the
dominant leg (i.e., kicking leg)
of each subject. The reliability
of strength measurements of
the isokinetic dynamometer
was previously validated (34).
Before the test, a warm-up was
carried out by means of 2 series
of 10 concentric actions
(30°s
21
) with increasing inten-
sities. Subjects were seated with
the hip at a 90°angle. To
minimize hip and thigh motion
during the contractions, straps
were applied across the chest
and pelvis and at midthigh.
Another strap secured the leg
to the Biodex lever arm, and
the alignment between the
center of rotation of the dyna-
mometer shaft and the axis of
the knee joint was checked at
the beginning of each trial. The
arms were positioned across
Figure 2. Ball speed during soccer kicking in electrostimulation group and control group. Measured values before
and after a wk-3 and a wk-5 period are means 6SD. *,**, and ***Significant difference between before, wk-3, and
wk-5 at p,0.05, p,0.01, and p,0.001, respectively.
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the chest with each hand clasping the opposite shoulder.
Strength measurements consisted of 2 series of 4 consecutive
maximal knee extensions and flexions from 90°of flexion
to full extension (0°). Contractions were performed at 3 ran-
domized angular velocities (concentric: +60 and +240°s
21
;
and eccentric: 260°s
21
), then 3 MVCs were performed in
isometric conditions at 60°. A 3-minute rest period was
allowed between series to eliminate the effects of fatigue. The
peak torque was directly measured by the Biodex software.
For each condition, only the best trial was included in the
analysis. Torques were gravity corrected at each joint angle,
using the resistive torque of the weight of the limb obtained
at the joint angle where the gravity effect was greatest.
Kicking Tests. Kicking performance was determined from
maximal ball speed during shots. The speed, was measured
with 44 Check Speed Radars (Tibar Industries, Downview,
Ontario, Canada). Check Speed Radars operate with
10.25-GHz frequency, and the frame of the signal is
approximately 60°vertical by 40°horizontal. Radars were
positioned in both upper and lower corners, behind the goal.
This goal was materialized on a net by means of an adhesive
strip (3 m wide and 2 m high). The soccer ball was placed at
a distance of 9 m. For speed values, we retained speed from the
radar nearest the ball impact. The ball characteristics were in
accordance with Fe
´de
´ration Internationale de Football
Association approval (size: 5, weight: 440 g, circumference:
69 cm, and pressure: 1,000 gcm
22
), and the pressure was
verified before each testing session. Shots were effectuated
using the dominant leg without run-up (one step before
kicking) and with run-up (3 steps before kicking). The best of
3 trials was analyzed for each subject.
Vertical Jump Tests. Each subject performed vertical jumps on
an Optojump system (Optojump, Microgate, Bolzano, Italy).
A digital timer was connected to the system to measure the
flight times of the jumps. The SJ was measured starting from
a static semisquatting position (knee angle 90°) and without
any preliminary movement. The countermovement jump
(CMJ) was performed starting from a standing position, then
squatting down to a knee angle of 90 65°and then extending
the knee in one continuous movement. During these tests,
the arms were kept close to the hips to minimize their
contribution. The third jump was a CMJ in which the
movement of the arms was free (CMJf ). The position of the
upper body was also controlled so as to minimize trunk
flexion and extension. Subjects were asked to jump as high as
they could 3 times, and the best performance was reported.
Sprint Test. Subjects performed 3 10-m sprints, separated by
3-minute recovery periods. Speed was measured with infrared
photoelectric cells positioned at 1 m from the floor and 10 m
from the start line and controlled by TAC (Test Atletici
Computerizzati, TEL.SI. s.r.l. Vignola, Italy) software. After
a visual signal, the players started from a standing position and
ran the 10-m distance as fast as possible. Performances did not
include reaction time. The fastest of 3 trials was used for
subsequent analysis.
Statistical Analyses
Standard statistical techniques were used to calculate means
and SDs. A 2-way analysis of variance (group 3time) with
repeated measures was used to compare MVC, jump height,
sprint, and ball speed. When significant effects occurred,
Tukey post hoc analyses were used to test significant
differences among values. Statistical power values were
calculated for various significant differences. The level of
significance was set at p#0.05 for all procedures. All
statistical tests were performed with Statistica software
(version 6.1, StatSoft, Tulsa, OK, USA).
RESULTS
Reliability of measurement showed that the statistical power
values for various significant differences ranged from 0.64
to 0.99.
Before training, EMS and C groups were similar in physical
characteristics, knee extensor strength, ball speed, vertical
jump, or sprint performance (p.0.05). No significant time
effect was observed for the C group in all tests (p.0.05).
Concerning the EMS group, eccentric torque increased
significantly at wk-3 (+11.5 610.4%, p,0.01) and wk-5
(+22.1 616.4%, p,0.001) as compared with before. A
further increase was observed from wk-3 to wk-5 (+9.6 6
8.1%, p,0.01) (Figure 1). A similar significant increase was
obtained in isometric conditions from before to wk-3 and wk-
5 (+16.3 621.3, p,0.01 and +27.1 622.6%, p,0.001,
respectively) and from wk-3 to wk-5 (+9.2 67.4%, p,0.05).
We observed no significant increment between before and
wk-3 for both concentric conditions. However, we observed
a significant increment between before and wk-5 (+14.0 6
9.9% at 60°s
21
and +23.2 618.9% at 240°s
21
,p,0.001)
TABLE 1. Vertical jump performance during SJ, CMJ,
and CMJf in EMS and C groups, mean values 6SD.*
SJ (cm) CMJ (cm) CMJf (cm)
EMS group
Before 32.0 66.4 35.1 66.5 40.9 66.1
wk-3 31.7 65.9 33.7 66.3 39.7 66.1
wk-5 33.1 66.2 35.9 65.9†41.6 65.1
C group
Before 29.7 64.4 34.4 64.7 40.5 65.8
wk-5 29.3 64.1 33.9 64.8 40.8 65.8
*SJ = squat jump; CMJ= countermovement jump;
CMJf = countermovement jump free; C = control; EMS =
electrostimulation.
†Significant difference between wk-3 and wk-5
(p,0.05).
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Electrostimulation in Soccer Players

and from wk-3 to wk-5 (+10.0 69.6% at 60°s
21
and +14.2 6
16.5% at 240°s
21
,p,0.01). Our measurements showed that
ball speed without run-up improved significantly at wk-3
(+6.6 68.7%, p,0.05) and wk-5 (+9.6 610.6%, p,0.001)
compared with measurements taken before the program. Ball
speed with run-up improved significantly at wk-5 (+5.6 6
4.0%, p,0.05) (Figure 2).
For jump performance, we observed a significant increase
from wk-3 and wk-5 in CMJ condition for the EMS group
(+6.7 66.3%, p,0.05) (Table 1). However, no significant
difference was observed in SJ, CMJ, and CMJf conditions at
wk-3 or wk-5 compared with before. Moreover, no signifi-
cant time effect was observed either in sprint time or velocity
after the wk-3 and wk-5 period in either group (Table 2).
DISCUSSION
The main finding of this study was that in addition to the well-
known strength increase, EMS training could lead to benefits
in more specific attributes such as kicking speed, with and
without run-up. However, strength gains were not directly
transferable to jumping ability or sprint performance in our
soccer players.
The results of the present study showed smaller strength
increases than those previously observed in elite ice hockey
players in eccentric conditions (12 vs. 24% in soccer players
and ice hockey players, respectively) after 3 weeks of EMS
training (7). However, these authors also found a significant
increase in the C group and explained gains in eccentric
conditions by noting the fact that subjects were more
accustomed to performing isokinetic contractions at pretests.
Furthermore, it was suggested that fast-twitch fibers might be
preferentially recruited during eccentric submaximal con-
tractions (22,33) and that total recruitment may take place
during eccentric maximal contractions (19). In addition,
Jubeau et al. (19) reported that EMS contractions may result
in neither motor unit recruitment according to Henneman’s
size principle nor in a reversal in this voluntary recruitment
order. Thus, a random recruitment of motor units during
EMS training may activate easily fast fibers in comparison
with voluntary contraction during submaximal level of force.
In our study, we suggested that eccentric adaptations may be
because of the result of motor unit recruitment. In fact,
Nardone et Schieppati (26) reported a greater fast MUs
recruitment during eccentric contraction.
The enhancements we observed in isometric conditions
corroborated the existing literature. For example, Gondin
et al. (16) observed an increment of 15% in the isometric
MVC of quadriceps muscles after 4 weeks of EMS training.
Early progress in strength production after wk-3 in isometric
but not in concentric conditions may be explained by the fact
that the angular position during EMS sessions was the same
as the isometric test position (i.e., 60°) (16). We also observed
that 2 additional weeks of EMS training induced significant
enhancements in MVCs in eccentric, isometric, and
concentric conditions. We would suggest that benefits
observed after 3 and 5 weeks of EMS training were mainly
because of neural adaptation. Indeed, it has been previously
reported that adaptations observed after 4 weeks of EMS
training on quadriceps muscles were mainly because of
neural adaptations, whereas changes in muscle mass and
architecture became significant between the fourth and the
eighth weeks (16). However, our measurements could not
confirm these previous adaptive mechanisms.
Research dealing with EMS training and kicking has until
now not been undertaken. This study reported an increase in
kicking performance without run-up after 3 weeks of EMS
training on the quadriceps muscle. Increments were higher
and significant after 5 weeks of EMS training in both
conditions (with and without run-up). We can thus suggest
that strength improvements are transferable to a specific
movement such as kicking in soccer players. This finding
confirms that quadriceps muscles play an important role
during kicking movements (2,28–30). Other studies have
found that EMS training could improve specific movements
in sports. Indeed, a beneficial effect in swimming sprint and
skating performance has previously been reported after 3
weeks of EMS training on latissimus dorsi and quadriceps
muscles, respectively (7,31). Conversely, Babault et al. (3)
found no improvement in a scrumming task after 6 weeks of
EMS training in elite rugby players. These authors explained
that the lack of gains in the scrum test may be partly
attributed to technical and motivational factors. Technical
considerations cannot, therefore, be excluded from criteria of
specific performance. Our results, therefore, suggest that
EMS training appears to be a viable approach for developing
specific attributes used in soccer.
We observed no significant increase in vertical jump
performance after 3 or 5 weeks of our EMS training program.
These results were in contradiction with Maffiuletti et al. (23)
who observed an increment of 14% in SJ after 4 weeks of
TABLE 2. Sprint time and velocity at 10 m in EMS and
C groups before, after wk-3, and after wk-5.*
10-m Sprint
time (s)
Velocity at
10 m (ms
21
)
EMS group
Before 1.91 60.06 6.83 60.37
wk-3 1.91 60.07 6.95 60.56
wk-5 1.90 60.05 6.83 60.29
C group
Before 1.91 60.06 7.24 60.70
wk-5 1.93 60.07 7.37 60.61
*EMS = electrostimulation; C = control.
Values are means 6SD.
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EMS training on quadriceps femoris. These different results
could be explained by the fact that fewer contractions were
performed in our study for each training session. However,
some previous studies were in accordance with our results
and reported no significant increase in vertical jump
performance. In fact, Malatesta et al. (25) and Herrero
et al. (17) reported no significant increase in SJ and CMJ after
4 weeks of EMS training on knee extensors. In addition,
a decrease in jumping ability after 3 weeks of EMS training in
ice hockey players has been reported (7). The lack of
increment or even decline in vertical jump performance
might be explained by fatigue or overtraining induced by
short EMS training programs. Some studies have reported
that a recovery period after EMS or resistance training is
necessary to allow an enhancement in jumping performance
(1,23–25). Furthermore, it has been previously demonstrated
that SJ and CMJ involve not only knee extensor muscles but
also plantar flexors (6,18). In this way, Malatesta et al. (25)
found a significant increase in mean height during consec-
utive CMJs after 4 weeks of EMS training of the quadriceps
femoris and triceps surae muscles. An increment in jump
performance may therefore necessitate training of more than
just the quadriceps femoris muscles. It has also been
previously reported that EMS training coupled with specific
training such as plyometric training induced gains in jump
ability (17). Indeed, plyometric training solicits quadriceps
muscles in the same way as jumping. Thus, an increase in
strength production of quadriceps muscles by EMS and the
specificity of plyometric training could induce an enhance-
ment in jumping ability.
Electrostimulation training induced adaptations on explo-
sive type movements such as sprint performance. In this
study, sprint time and velocity at 10 m did not change
significantly after 3 and 5 weeks of EMS training. These
findings are contradictory to those of a previous study. Indeed,
Herrero et al.(17) reported a significant improvement in 20-m
sprint performance after 4 weeks of EMS training on
quadriceps muscles. The lack of gain in sprint performance in
our study could be explained by the complexity of the
running task in which many muscles are involved and by the
technical level of the amateur soccer players tested here. The
transfer of strength gains after EMS training appeared more
difficult for nonspecific sport performance (i.e., vertical jump
and sprint) than specific sport performance (i.e., kicking) in
soccer players.
PRACTICAL APPLICATIONS
In summary, soccer necessitates not only technical and
strategic training, but also physical conditioning. Three weeks
of EMS training programs seems appropriate to improve knee
extensors muscle strength in eccentric and isometric
conditions in soccer players. However, 2 additional weeks
appears necessary to observe increments in all contractile
conditions. Moreover, EMS training leads to an improvement
in specific soccer tasks such as ball speed performance after
kicking. Exclusive EMS training of the quadriceps femoris
muscles may be of limited value for improving jumping
performance in amateur soccer players. However, some of the
following might provide a significant training effect for
jumping including (a) the concurrent training of the triceps
surae, gluteus maximus, and hamstrings, (b) the inclusion of
an optimal recovery period, and (c) the coupling of EMS
training with plyometric training. Additionally to traditional
soccer training, an EMS training program of 3- or 5-week
period appears to represent a viable means for improving force
and specific soccer tasks at preseason and during the season.
In fact, this original method might be used to complement
traditional training for soccer. It would infuse variability into
the training program, which might enhance the motivation
of some players. Furthermore, EMS might also be used for
injured athletes to attenuate or eliminate detraining effects.
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