EFFECTS OF IN-SEASON SHORT-TERM PLYOMETRIC
TRAINING PROGRAM ON LEG POWER, JUMP- AND
SPRINT PERFORMANCE OF SOCCER PLAYERS
MOHAMED SOUHAIEL CHELLY,1,2 MOHAMED ALI GHENEM,3 KHALIL ABID,1 SOUHAIL HERMASSI,1,2
ZOUHAIR TABKA,3 AND ROY J. SHEPHARD4
1
Research Unit ‘‘Evaluation and analysis of factors influencing sport performance’’, Higher Institute of Sport and Physical
Education of Ksar Said, Tunis, Tunisia; 2Higher Institute of Sport and Physical Education of Ksar Said, Tunis, Tunisia;
3
Laboratory of Physiology, Faculty of Medicine Ibn-El-jazzar, Sousse, Tunisia; and 4Faculty of Physical Education and Health,
University of Toronto, Toronto, Ontario, Canada
ABSTRACT
Chelly, MS, Ghenem, MA, Abid, K, Hermassi, S, Tabka, Z, and
Shephard, RJ. Effects of in-season short-term plyometric
training program on leg power, jump- and sprint performance
of soccer players. J Strength Cond Res 24(10): 2670–2676,
2010—Our hypothesis was that the addition of an 8-week lower
limb plyometric training program (hurdle and depth jumping) to
normal in-season conditioning would enhance measures of
competitive potential (peak power output [PP], jump force, jump
height, and lower limb muscle volume) in junior soccer players.
The subjects (23 men, age 19 6 0.7 years, body mass 70.5 6
4.7 kg, height 1.75 6 0.06 m, body fat 14.7 6 2.6%) were
randomly assigned to a control (normal training) group (Gc;
n = 11) and an experimental group (Gex, n = 12) that also
performed biweekly plyometric training. A force–velocity
ergometer test determined PP. Characteristics of the squat
jump (SJ) and the countermovement jump (CMJ) (jump height,
maximal force and velocity before take-off, and average power)
were determined by force platform. Video-camera kinematic
analyses over a 40-m sprint yielded running velocities for the
first step (VS), the first 5 m (V5m) and between 35 and 40 m
(Vmax). Leg muscle volume was estimated using a standard
anthropometric kit. Gex showed gains relative to controls in PP
(p , 0.01); SJ (height p , 0.01; velocity p , 0.001), CMJ
(height p , 0.001; velocity p , 0.001, average power p ,
0.01) and all sprint velocities (p , 0.001 for V5m and Vmax, p ,
0.01 for VS). There was also a significant increase (p , 0.05) in
thigh muscle volume, but leg muscle volume and mean thigh
cross-sectional area remain unchanged. We conclude that
Address correspondence to Dr. Mohamed Souhaiel Chelly, csouhaiel@
yahoo.fr.
24(10)/2670–2676
Journal of Strength and Conditioning Research
Ó 2010 National Strength and Conditioning Association
2670
the
biweekly plyometric training of junior soccer players (including
adapted hurdle and depth jumps) improved important components of athletic performance relative to standard in-season
training. Accordingly, such exercises are highly recommended
as part of an annual soccer training program.
KEY WORDS depth jump, running velocity, muscle volume,
stretch-shortening cycle, jumping, force–velocity test
INTRODUCTION
S
trength, power, and their derivatives (acceleration,
sprinting, and jumping) all make important contributions to the performance potential of soccer
players (17). During a typical game, a 2- to 4-second
sprint occurs every 90 seconds (4,29); sprinting occupies
some 3% of playing time and accounts for 1–11% of the
distance covered during a match (29,32). Some 96% of sprints
are shorter than 30 m, and 49% are ,10 m (32). Thus, the
performance over distances of 10 m or less, and the velocity
attained during the first step are key indicators of player
potential (8,9). A soccer match also demands numerous
explosive movements, including some 15 tackles, 10 headings, frequent kicking, and changes of pace (3,4,32,39).
Jumping ability and anaerobic performance are critical to
the soccer player, and high scores for the squat counter
movement jumps (CMJs) are to be anticipated in top players
(0.40 and 0.65 m, respectively, in 1 study [32]). Soccer is
becoming progressively more athletic, and short-term muscle
power has become crucial in many game situations.
The power that an individual can develop depends on both
force and velocity, as determined by friction-loaded ergometers (9,34). Both linear force– and parabolic power–
velocity are increased slightly after 8 weeks of heavy
resistance training (9). Strength training is thus popular as
a means of augmenting muscular power and performance in
soccer players (9,17,31,32). In 1 study, 7 weeks of lower limb
strength training with external loads of 50 kg induced
respective increases in 1 repetition maximum (1RM) half
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squat, CMJ height, SJ height, peak power (PP), 0- to 10-m
sprint time and 0- to 40-m sprint time of 26, 5, 7, 7.5, 1.7, and
1.3% (31). Likewise, Chelly et al. (9) reported that 8 weeks of
half squat training with heavy loads enhanced SJ height (p ,
0.05), lower limb PP (p , 0.05), 1RM half back squat (p ,
0.001), and sprint velocities (p , 0.05).
Less is known about benefits to the soccer player from the
alternative or supplementary tactic of plyometric training.
Plyometric exercise involves stretching the muscle immediately
before making a rapid concentric contraction. The combined
action is commonly called a stretch-shortening cycle (SSC).
Nevertheless, the use of SSC seems a particularly appropriate
regimen for soccer, where players must frequently jump, run,
and sprint. Similar gains of maximal strength have been
reported with traditional strength and plyometric training, but
the latter approach appears to induce greater gains in muscle
power (36). Currently available findings regarding jump height
and sprint performance are contradictory. In 1 study, 6 weeks
of depth jump or CMJ training improved the vertical jump
height (p , 0.05) of youth soccer players, but their sprint
performance remained unchanged (p . 0.05) (33). Likewise,
Markovic et al. (22) found that 10 weeks of plyometric training
increased squat jump (SJ) and CMJ height and power, but the
20-m sprint time remained unchanged. In contrast, Rimmer
and Sleivert (30) found that 8 weeks of plyometric training
improved 0- to 10-m and 0- to 40-m sprint times (p = 0.001).
Most previous plyometric investigations have been completed
preseason. De Villarreal et al (11) recently noted significant
decreases in 20-m sprint time and jump height (CMJ and drop
jump) if a 7-week plyometric training program was followed
by 7 weeks of detraining.
Given the contradictory nature of existing information on
the efficacy of plyometric training (12), our aim was to
examine the effect of adding a combined hurdle and depth
jump program to the normal in-season regimen of experienced soccer players. We hypothesized that 8 weeks of
biweekly plyometric training would enhance leg PP, jump
height, and sprint running velocity relative to players who
maintained their normal in-season regimen.
METHODS
Experimental Approach to the Problem
This study addressed the question as to whether 8 weeks of
biweekly in-season plyometric training would enhance the
physical performance of soccer players relative to their
customary in-season training regimen. A team of experienced
soccer players was divided randomly into a Plyometric
training group (Gex; n = 12) and a control group (standard inseason regimen) (Gc; n = 11). Two weeks before definitive
testing, 2 familiarizations sessions were held. Definitive
measurements began 4 months into the competitive season.
Data were collected before enhanced training, and after
completing the 8-week trial. The protocol included a force–
velocity test to evaluate leg PP, maximal pedaling velocity
(V0) and maximal force (F0); SJ and CMJ to assess leg jump
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power, velocity and leg force; a 40-m sprint that evaluated
velocity during the first step, 5-m velocity and maximal
running velocity, and anthropometric assessments of lower
limb muscle volumes. Initial and final tests were carried out at
the same time of the day, and under the same experimental
conditions, at least 3 days after the most recent competition.
Players maintained their normal intake of food and fluids, but
before testing, they abstained from physical exercise for 1
day, drank no caffeine-containing beverages for 4 hours, and
ate no food for 2 hours. Verbal encouragement ensured
maximal effort throughout the performance tests.
Subjects
All procedures were approved by the Institutional Review
Committee for the ethical use of human subjects, according to
current national laws and regulations. Participants gave written
informed consent after receiving both a verbal and a written
explanation of the experimental protocol and its potential risks.
Subjects were told that they could withdraw from the trial
without penalty at any time. Twenty-three male players were
drawn from a single regional soccer team (age 19 6 0.7 years,
body mass 70.5 6 4.7 kg, height 1.75 6 0.06 m, body fat 14.7 6
2.6%). Their mean soccer experience was 7.2 6 1.2 years. All
were examined by the team physician, with a particular focus on
conditions that might preclude plyometric training, and all were
found to be in good health. The 23 individuals were randomly
assigned between 2 groups: plyometric training (Gex; n = 12;
age 19.1 6 0.7 years, body mass 70.3 6 5.5 kg, height
1.76 6 0.06 m, body fat 14.7 6 3.2%) and control (Gc; n = 11; age
19.0 6 0.8 years, body mass 70.6 6 4.2 kg, height 1.74 6 0.06 m,
body fat 14.6 6 1.7%).
Procedures
The study was performed over an 8-week period, from
January to March. All subjects had engaged in the standard
training regimen from the beginning of the football season
(September) until the end of the study (March). Before the
competitive season (August), all subjects (Gex and Gc) were
engaged in a light resistance training program for both the
upper and the lower limbs. Twice weekly sessions included
exercises using the body weight as a resistance. During the
competitive season (September to March), subjects trained
5 times a week and played one official game. The standard
training sessions lasting 90 minutes included skill activities at
various intensities, offensive and defensive tactics, and
30 minutes of continuous play. The control group maintained
this pattern, but during the period January through March, the
experimental group supplemented this standard regimen by
a specific plyometric program. All subjects also engaged in
weekly school physical education sessions; these lasted for
40 minutes and consisted mainly of ball games.
Tests were completed in a fixed order over 2 consecutive
days. Care was taken to ensure that those undertaking
plyometric training were tested 5–9 days after their last
plyometric session to ensure adequate recovery from the
acute effects of training.
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In-Season Plyometric Training in Male Soccer Players
Testing Schedule
Subjects were familiarized with circuit training for 2 weeks
before beginning either measurements or formal training.
Testing was integrated into the weekly training schedule.
A standardized battery of warm-up exercises was performed
before maximal efforts. On the first test day, subjects
performed the SJ and CMJ, followed by the force–velocity
test. Anthropometrical assessment and sprint running were
undertaken on day 2.
Day 1. Squat and countermovement jumps: Characteristics of the
SJ and the CMJ (jump height, maximal force before take-off,
maximal velocity before take-off, and the average power of
the jump) were determined using a force platform (Quattro
Jump, version 1.04, Kistler Instrument AG, Winterthur,
Switzerland). Jump height was determined as the center of
mass displacement, calculated from the recorded force and
body mass. Subjects began the SJ at a knee angle of 90°,
avoiding any downward movement, and they performed
a vertical jump by pushing upward, keeping their legs straight
throughout. The CMJ was begun from an upright position,
making a downward movement to a knee angle of 90° and
simultaneously beginning to push-off. One minute of rest was
allowed between 3 trials of each test, the largest jump being
used in subsequent analyses.
The force–velocity test: The force–velocity test was performed on a mechanically braked cycle ergometer (Monark
894 E Ergometer, Vansbro, Sweden). A familiarization
session was conducted on a separate day. Individuals
completed 5 short maximal sprints against braking forces
corresponding to 2.5, 5, 7.5, 9, and 11.5% of the individual’s
body mass, with rest intervals of at least 5 minutes between
trials. Software allowed estimation of velocity, braking force,
and power output during each trial. Peak power was judged
to have been reached when additional loading induced
a decrease in power output. Relationships between braking
force and pedaling velocity were plotted for each individual.
Maximal pedaling velocity (V0) and maximal force (F0) were
calculated using an accepted regression equation (2,34).
Day 2. Anthropometry: Standard equations were used to
predict body fat from the biceps, triceps, subscapular, and
suprailiac skinfolds (40). Muscle volumes for the thigh and
the leg were estimated from multiple measurements of
skinfolds, citcumferences, and diameters for the lower limbs,
as detailed elsewhere (19).
Sprint performance: Subjects sprinted on a grass track for
40 m. In normal play, a sprint usually starts from a standing or
jogging position, but in our tests, subjects began the sprint
from a standing position to allow estimation of velocity
during the first step. Video cameras (Sony Handycam, DCRPC105E, Ó 2003 Sony corporation, Tokyo, Japan) were
placed perpendicular to the running lane. The first camera
filmed the first 5 meters, and the second the phase of maximal
running velocity (from 35 to 40 m) (9,10,23). Recorded data
2672
the
TABLE 1. Training program for plyometric group.
Week
1
2
3
4
5
6
7
8
Exercise 3 sets 3 reps
40-cm
40-cm
40-cm
60-cm
40-cm
40-cm
40-cm
40-cm
hurdle jump 3 5 3 10
hurdle jump 3 7 3 10
hurdle jump 3 10 3 10
hurdle jump 3 5 3 10
drop jumps 3 4 3 10
drop jumps 3 4 3 10
drop jumps 3 4 3 10
drop jumps 3 4 3 10
included the average velocity during the first step (VS), the
first 5 m (V5m) and between 35 and 40 m (Vmax). Two trials
were separated by at least 5 minutes, the highest of the paired
values being retained. Software (Regavi & Regressi, Micrelec,
Coulommiers, France) converted hip displacements to the
corresponding velocities (VS, V5m, and Vmax). The technique,
including the reliability of the camera and data processing
software, has previously been detailed (9).
Details of plyometric training: Subjects in both experimental
and control groups avoided any training other than that
associated with the soccer team. Each Tuesday and Thursday
for 8 weeks, Gex supplemented the standard regimen with
plyometric training, performed immediately before their
standard training sessions (Table 1). Plyometric sessions
began with a 15-minute warm-up and lasted for some
TABLE 2. Intraclass correlation coefficient showing
acceptable reliability of track running velocities and
jump tests.*
Track running velocity
VS (ms21)
V5 (ms21)
Vmax (ms21)
Jump tests
SJ height (m)
SJ force (N)
SJ velocity (ms21)
SJ power (Wkg21)
CMJ (m)
CMJ force (N)
CMJ velocity (ms21)
CMJ power (Wkg21)
ICC
95% CI
0.86
0.90
0.84
0.67–0.94
0.77–0.96
0.62–0.93
0.97
0.86
0.95
0.85
0.98
0.82
0.96
0.95
0.92–0.99
0.54–0.96
0.84–0.98
0.48–0.95
0.95–0.99
0.38–0.94
0.88–0.99
0.85–0.98
*ICC = intraclass correlation coefficient; CMJ =
countermovement jump; SJ = squat jump; CI = confidence
interval.
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comprised 10 maximal rebounds after dropping from a 0.4-m
box, with a pause of 5 seconds between each rebound (22).
TABLE 3. Anthropometric parameters before and
after plyometric training.*†‡
Test Gex (n = 12)
Total leg
muscle
volume (L)
Thigh muscle
volume (L)
Mean thigh
CSA (cm2)
Pre
Post
8.7 6 0.8
9.0 6 0.9
Statistical Analyses
Gc (n = 11)
9.6 6 1.0
9.6 6 0.8
Pre
4.0 6 0.4
6.6 6 0.7
Post
4.1 6 0.5§
6.7 6 0.5
Pre 176.4 6 13.8 194.9 6 25.3
Post 182.3 6 16.3 193.3 6 23.2
Gex = plyometric training group; Gc = control group;
CSA ¼ cross sectional area.
*p , 0.05.
†Values are given as mean 6 SD.
‡A 2-way analysis of variance with repeated measure
(group 3 time) was used to assess the statistical
significance of training related effects.
30 minutes. Jumps were performed on a grass track. Subjects
were instructed to perform all exercises with maximal effort.
Each jump was performed to reach the maximal possible
height with a minimal ground contact time. Both hurdle and
drop jumps were performed with small angular knee
movements; the ground was touched with the balls of the
feet only, thereby specifically stressing the calf muscles (22).
Each set of hurdles consisted of 10 continuous jumps over
hurdles spaced at intervals of 1 m. Each set of drop jumps
Means and SDs were calculated using standard statistical
methods. Training related effects were assessed by a 2-way
analysis of variance with repeated measure (group 3 time). If a
significant F value was observed, Sheffé’s post hoc procedure
was applied to locate pairwise differences. Percentage changes
were calculated as ([posttraining value 2 pretraining value]/pre training value) 3 100. Pearson product–moment
correlations determined relationships between braking force
and pedaling velocity. The reliabilities of sprint velocities (VS,
V5m, and Vmax) and vertical jump (SJ and CMJ) height,
velocity, force, and average power measurements were
assessed using intraclass correlation coefficients (ICCs) (28).
As a general rule, an ICC over 0.90 is considered to be high,
between 0.80 and 0.90 moderate and below 0.80 to be
insufficient for physiological field testing (35); ICCs showed an
acceptable reliability for our measurements of track velocity
and jump tests (Table 2). We accepted p # 0.05 as our criterion
of statistical significance, whether a positive or a negative
difference was seen (i.e., a 2-tailed test was adopted).
RESULTS
Plyometric training induced a significant increase in thigh
muscle volume (p , 0.05); measures of total leg muscle and
thigh cross sectional area (CSA) showed a similar directional
trend, but because of greater variability were not statistically
significant (Table 3). Force–velocity test data also showed
increases of absolute PP (W) and PP relative to body mass
TABLE 4. Force–velocity test calculated parameters before and after plyometric training.*†‡
Absolute power (W)
Power (Wkg21)
Power (W/total leg muscle volume)
Power (W/thigh muscle volume)
Power (W/CSA) (Wcm22)
Maximal pedaling velocity (rpm)
Maximal force (N)
Test
Gex (n = 12)
Pre
Post
Pre
Post
Pre
Post
Pre
Post
Pre
Post
Pre
Post
Pre
Post
711 6
743 6
10.1 6
10.7 6
81.8 6
82.8 6
177.4 6
181.2 6
4.0 6
4.1 6
176.1 6
182.2 6
84.4 6
83.0 6
84
87§
0.7
1.0§
6.8
7.6
15.4
16.8
0.4
0.4
10.3
7.9
8.5
6.1k
Gc (n = 11)
680
682
9.6
9.6
71.0
71.4
103.5
101.7
3.6
3.6
170.2
170.0
84.6
84.5
6 128
6 129
6 1.5
6 1.6
6 12.8
6 12.9
6 19.3
6 17.5
6 0.9
6 1.0
6 14.7
6 16.6
6 4.4
6 3.7
*Gex = plyometric training group; Gc = control group.
†Values are given as mean 6 SD.
‡A 2-way analysis of variance with repeated measure (group 3 time) was used to assess the statistical significance of training related
effects.
§p , 0.01.
k
p , 0.05.
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In-Season Plyometric Training in Male Soccer Players
TABLE 5. Jumps test values before and after
plyometric training.*†‡
Test Gex (n = 12)
SJ
Height (m) Pre
Post
Velocity
Pre
(ms21) Post
Force (N) Pre
Post
Power (W) Pre
Post
Power
Pre
(Wkg21) Post
CMJ jump
Height (m) Pre
Post
Velocity
Pre
(ms21) Post
Force (N) Pre
Post
Power (W) Pre
Post
Power
Pre
(Wkg21) Post
Gc (n = 11)
0.36 6 0.03
0.39 6 0.03§
2.4 6 0.1
2.5 6 0.4k
1,540 6 141
1,590 6 168
1,398 6 145
1,511 6 197
19.9 6 2.1
21.7 6 2.5
0.37
0.37
2.1
2.1
1,504
1,589
1,451
1,464
20.5
20.7
6 0.02
6 0.02
6 0.2
6 0.1
6 167
6 160
6 150
6 161
6 1.4
6 1.7
0.40 6 0.03
0.41 6 0.03k
2.5 6 0.1
2.6 6 0.1k
1,347 6 111
1,372 6 108
1,673 6 147
1,753 6 170{
23.9 6 2.2
25.2 6 1.6§
0.39
0.39
2.2
2.2
1,313
1,345
1,612
1,612
22.8
23.1
6 0.02
6 0.02
6 0.2
6 0.1
6 133
6 147
6 176
6 161
6 1.6
6 1.4
*Gex = plyometric training group; Gc = control group;
CMJ = countermovement jump; SJ = squat jump.
†Values are given as mean 6 SD.
‡A 2-way analysis of variance with repeated measure
(group 3 time) was used to assess the statistical
significance of training related effects.
§p , 0.01.
k
p , 0.001.
{p , 0.05.
TABLE 6. Sprint running velocities values before and
after plyometric training.*†‡
Test
21
VS (ms
)
Pre
Post
V5 (ms21)
Pre
Post
Vmax (ms21) Pre
Post
Gex (n = 12) Gc (n = 11)
2.2 6
2.6 6
4.0 6
4.4 6
8.2 6
9.0 6
0.3
0.3§
0.5
0.4k
0.2
0.2k
2.0 6 0.2
2.2 6 0.3
3.6 6 0.3
3.7 6 0.3
7.8 6 0.3
8.0 6 0.3
*Gex = plyometric training group; Gc = control group.
†Values are given as mean 6 SD.
‡A 2-way analysis of variance with repeated measure
(group 3 time) was used to assess the statistical
significance of training related effects.
§p , 0.01.
k
p , 0.001.
2674
the
(Wkg21) (Table 4, p , 0.01); however, there was no increase
of PP per unit of muscle volume or thigh muscle volume
(Table 4), and maximal force even showed a small decrease.
Data for SJ and CMJ were in accordance with these findings
(Table 5), with a significant increase in SJ height relative to
Gc (p , 0.01), increases in CMJ height and average jump
power (W), but no significant increase in force after
plyometric training. The increase in jump test scores was
accompanied by a significant increase of running velocities
(p , 0.001 for both V5m and Vmax; p , 0.01 for VS) (Table 6).
DISCUSSION
The main finding from this study is that, in accordance with
our hypothesis, the supplementary plyometric training program increased several measures of potential soccer playing
performance, including the absolute (W) and the relative
(Wkg21) PP of the legs, as assessed by force–velocity tests
(p , 0.001, Table 4), SJ, CMJ, and sprint running, scores
(Tables 5 and 6).
Improvements of muscle power and vertical jump height
with plyometric training have been described previously
(7,18,21). A recent meta-analysis (12) found gains in jump
height of 4.7–15% after plyometric training. Our results are
consonant with these finding (SJ and CMJ scores were
increased by 7.1 and 4.2%, respectively). The plyometric
training program that we used is similar to that proposed by
Markovic et al. (22); they observed increases in both SJ and
CMJ scores relative to controls (p , 0.05), but the PP of the
SJ relative to body mass (Wkg21) did not improve. Our
results accord with these findings (Table 5). In contrast, the
PP of the CMJ was significantly higher for Gex than for Gc.
This may be because the CMJ involves an SSC and is thus
very similar to the plyometric exercises used in our study.
Moreover, plyometric training is likely to improve coordination (12) and thus to induce a neuromuscular
adaptation that augments power production (5). Behm
et al. (5) suggested that any increase of leg PP induced by
plyometric is essentially because of neuronal adaptations:
selective activation of motors units, synchronization, selective activation of muscles, and increased recruitment of
motor units. Many of the CMJ parameters (jump height,
velocity, absolute [W], and relative power [Wkg21]) tended
to increase more than values for SJ (Table 5), again reflecting
similarity between the CMJ and plyometric training. Both
CMJ absolute (W) and relative (Wkg21) power were
significantly improved after plyometric training, but the
peak force showed no statistically significant change; this
implies that the improvement in CMJ power production was
largely because of an increase in peak velocity.
Lower limb muscle volumes tended to increase after
plyometric training, significantly so for thigh muscle volume
(Table 3, p , 0.05). The gain in SJ average power per unit of
muscle volume (W/Lm) was much smaller than gains in
absolute values (W) or relative to body mass (Wkg21) (4.9, vs.
8.3 and 9.3% W and Wkg21, respectively) (Table 3). Likewise,
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the gain in CMJ average power per unit of muscle volume was
only 1.6%, as compared with 4.9 and 5.9% for W and Wkg21,
respectively. These results suggest that in addition to
neuromuscular adaptations, our plyometric training induced
an increase in leg muscle volume and average power
production. The same conclusion can be drawn from the cycle
ergometer data (Table 5) (PP gains of 4.6 and 6.2% for W and
Wkg21, respectively, dropping to 1.4% W/Lm); indeed, gains
of leg muscle volume seem the main determinant of the gain in
PP as assessed by the force–velocity test.
Several previous studies have suggested that plyometric
training can enhance sprinting ability because it uses the SSC.
Mero et al. (24) found a close relationship (p , 0.001)
between the rise of the center of gravity in a drop jump and
maximal running velocity. Drop jump and CMJ performance
also bear significant relationships to 30- and 40-m sprint
times (15,26). Our investigation showed improved sprint
speeds after plyometric training (Table 6). To our knowledge,
this is the first study to investigate the effect of short-term
supplementary plyometric training on the sprint performance of soccer players. However, previous research has
demonstrated that the velocity over distances of 0–30, 10–20,
and 20–30 m is increased significantly (p , 0.05) after 10
weeks of plyometric training (21). A 12-week period of
nondepth jump plyometric exercise also improved the 25-m
sprint performance of entry-level collegiate athletes by 9%
(25). Similarly, 6 weeks of plyometric training decreased
50-m sprint times in 9 adult male athletes and a group of
basketball players (37). In contrast, Herrero et al. (16) found
no significant gains of SJ height, CMJ height or 20-m sprint
time with plyometric training, and Markovic et al. (22) found
no improvements in 20-m sprint times, even though they
used a similar training program to us. These discrepancies
may reflect differences in methodology or the fitness level of
the subjects (physical education students vs soccer players).
The meta-analysis of De Villarreal et al. (12) concluded that
subjects with the most sport experience showed the greatest
increases in vertical jump height. This could also be true of
sprint performance, explaining some of the discrepant results.
Differences in the training protocol may also be a factor. In
the study of Herero et al. (16), training consisted of horizontal
and drop jumps continued 2 d wk21 for only 4 weeks; in our
study, training was more intense (hurdle and depth jumps)
and continued for longer (twice a week for 8 weeks).
Maximal intensity sprinting necessitates extremely high
levels of neuronal activation (13,27). Measurable neurological
parameters such as nerve conduction velocity, maximum
electromyogram, motor unit recruitment strategy, and
Hoffman reflex (H-reflex) all alter in response to physical
training (6,14,20). Potential mechanisms for improvements
in sprint performance include changes in temporal sequencing of muscle activation for more efficient movement,
preferential recruitment of the fastest motor units, increased
nerve conduction velocity, frequency or degree of muscle
innervations, and increased ability to maintain muscle
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recruitment and rapid firing throughout the sprint (1).
Wilkerson et al. (38) showed that 6 weeks of preseason
plyometric jump training improved neuromuscular attributes
in 11 basketball players. In the present study, we did not
assess neuronal adaptations, but we can assume from earlier
studies that the plyometric training induced neuromuscular
adaptations and that these adaptations contributed to the
observed gains in sprint performance.
PRACTICAL APPLICATIONS
The current study indicates that in male regional junior soccer
players 8 weeks of supplementary biweekly in-season
plyometric training with suitably adapted hurdle and depth
jumps substantially enhances leg PP output, jump height, and
sprint velocities over both acceleration (0–5 m) and maximal
speed (0–40 m) phases. We found it quite practical to add this
short-term plyometric training program to traditional inseason technical and tactical male soccer training sessions to
enhance the performance potential of our players. The gains
that were realized seem greater than could have been
anticipated from a corresponding extension of traditional
training (although this point needs further checking). In
addition to effects stemming from the observed increases in
muscle volume, there are many potential neuromuscular
explanations of the response to plyometric training, and these
merit further investigation. As the mechanisms become more
fully understood, even larger gains of performance may be
realized for a similar increase of training volume.
ACKNOWLEDGMENT
The authors would like to thank the ‘‘Ministére de l’enseignement supérieur et de la Recherche Scientifique, Tunisia’’ for
financial support.
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