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What are the effects of youth training and its implication on sports. Using the article selected summarize it in one page. Include citations in APA format. Times New Roman size 12 font.

Division of Sport Sciences, Northumbria University, Newcastle-upon-Tyne, United Kingdom; and
English Institute of Sport, Gateshead, United Kingdom
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Thomas, K, French, D, and Hayes, PR. The effect of two plyometric
training techniques on muscular power and agility in youth soccer
players. J Strength Cond Res 23(1): 332–335, 2009—The aim of
this study was to compare the effects of two plyometric training
techniques on power and agility in youth soccer players. Twelve
males from a semiprofessional football club’s academy (age =
17.3 6 0.4 years, stature = 177.9 6 5.1 cm, mass = 68.7 6 5.6
kg) were randomly assigned to 6 weeks of depth jump (DJ) or
countermovement jump (CMJ) training twice weekly. Participants
in the DJ group performed drop jumps with instructions to
minimize ground-contact time while maximizing height. Participants in the CMJ group performed jumps from a standing start
position with instructions to gain maximum jump height.
Posttraining, both groups experienced improvements in vertical
jump height (p , 0.05) and agility time (p , 0.05) and no change
in sprint performance (p . 0.05). There were no differences
between the treatment groups (p . 0.05). The study concludes
that both DJ and CMJ plyometrics are worthwhile training activities
for improving power and agility in youth soccer players.
KEY WORDS plyometrics, depth jump, countermovement,
stretch-shortening cycle
lyometric training—jumping, bounding, and hopping exercises that use the stretch shortening cycle
of the muscle unit—have consistently been shown
to improve the production of muscle force and
power (15,30). In particular, the fast force production of
the trained muscle improves, coupled with smaller increases
in maximum isometric force (15). These physiological
adaptations have facilitated increases in vertical jump height
Address correspondence to Kevin Thomas, kevin2.thomas@northumbria.
Journal of Strength and Conditioning Research
Ó 2009 National Strength and Conditioning Association
(8,14,30,31) and decreases in sprint and acceleration times
Some research in plyometrics has investigated the effect of
exercise mode on performance. Countermovement jump
(CMJ) and depth jump (DJ) training have both improved
vertical jump height, with no significant difference between
the two modalities (8,14,17). Bobbert (4) has speculated
that using CMJ or DJ techniques may result in differences
in training adaptations, arguing that a DJ would trigger
improvement in the power output capacity of muscles,
whereas repetition of the CMJ would improve coordination.
Young et al. (34) attempted to investigate these assumptions,
but their study was hampered by an inadequate training
volume and intensity.
The potential improvements from plyometrics as measured
by vertical jump and sprint performance would be beneficial
to soccer (2,23). The basic movement patterns in soccer also
require high levels of agility (11,24). Agility requires rapid
force development and high power output, as well as the
ability to efficiently utilize the stretch shortening cycle in
ballistic movements (21). Plyometric training has been
shown to improve these requirements (1,5,15), and Besier
et al. (3) have recommended the inclusion of plyometrics in
soccer training to familiarize players with unanticipated
changes in direction. The aim of the present study was to
compare the effectiveness of CMJ and DJ plyometric training
modalities on muscular power and agility in soccer players.
Experimental Approach to the Problem
Using a randomized, between-group design, 12 soccer players
were assessed for leg power, sprint speed, and agility pre and
post 6 weeks of DJ or CMJ training.
After institutional ethics approval, 15 males from a semiprofessional soccer academy gave written informed consent
to take part in the study after completion of a screening
questionnaire. Parental consent was obtained for participants
under 18 years of age. The study was conducted in season,
where participants attended soccer training two to four times
per week and played competitive matches at least once
Journal of Strength and Conditioning Research
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Journal of Strength and Conditioning Research
a week. All participants had been involved in soccer training
of this regularity for . 4 years before the study. Participants
were randomly assigned to DJ and CMJ jump groups. Twelve
participants (age = 17.3 6 0.4 years, height = 177.9 6 5.1 cm,
weight = 68.7 6 5.6 kg) successfully completed the study.
Training. Plyometric training was undertaken twice a week
for 6 weeks. Participants in the CMJ group performed exercises that always began with a countermovement, defined as
a flexion of the knees. During rebound exercises, participants
in this group were told to ‘‘damp’’ their landings each time and
to gain maximum height through knee flexion. Participants in
the DJ group performed exercises that always began with
a drop from a height (40 cm). Participants in the DJ group
were instructed to minimize ground-contact time while
maximizing height. These instructions were emphasized
during every session through the use of demonstrations,
verbal cues, and exercise sheets.
The intensity of each program was subjectively equated
using Chu’s (7) and Potach and Chu’s (22) classification of
plyometric exercise intensities. The type of exercise that each
group performed was matched by intensity and, where
possible, by similar jumps. The height of the DJ box remained
at 40 cm to ensure that intensity increased as a function of
exercise and not as a function of increased eccentric load,
which could not be manipulated in the CMJ condition.
Sessions began at 80 foot contacts and progressed to 120 by
the end of training (22). The program was incorporated into
their usual twice-weekly training regime. Participants also
continued their usual competitive program of matches.
Participants were asked to refrain from any other form of
training that could affect the variables measured.
Testing. Participants were tested pre and post the 6-week
training period. Before testing, participants performed a 5-minute warm-up protocol consisting of submaximal running, active
stretching, and jumping exercises. This warm-up was chosen
because of its positive effects on power production (32). Table 1
shows the test-retest limits of agreement and intraclass
correlations for each dependent variable.
Countermovement vertical jump height (cm) was measured using a vertical jump mat and belt (Takei Jump Meter,
Japan). Participants were instructed to keep their hands on
their hips at all times and were permitted two trials (. 15
seconds of recovery) to practice jumping technique followed
by two recorded jumps. Light gates were used to measure
sprint speed and agility (NewTest, Kiviharjuntie, Finland).
Sprint speed from a standing start was assessed for 20 m with
5-m splits. Each participant completed three trials—one
practice and two recorded with at least 4 minutes of recovery
between each trial. The 505 agility test was employed to
assess agility. The 505 agility test is designed to minimize the
influence of individual differences in running velocities while
accentuating the effect of acceleration immediately before,
during, and after the change of direction (11). Participants
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TABLE 1. Limits of agreement (LOA) and intraclass
correlations (ICC) for outcome measures.
5 m (s)
10 m (s)
15 m (s)
20 m (s)
Agility 505 (s)
CMJ (cm)
0.01 6 0.12
0.01 6 0.13
0.01 6 0.18
0.01 6 0.15
0.01 6 0.05
CMJ = countermovement jump.
completed three trials each—one practice and two recorded
with at least 4 minutes of recovery between each trial.
Statistical Analyses
Descriptive statistics are represented as mean (SD). The mean of
the recorded jumps was used as the score for CMJ height. The
best times for 5, 10, 15, and 20 m were used as the final results
(11). The fastest agility score was used in the analyses. Tests of
normal distribution (Kolmogorov-Smirnov and Levene’s) were
conducted on all data before analysis. All data were normally
distributed (p . 0.05). A mixed-factorial ANOVA with repeated
measures on one factor assessed main effects for time, group,
and the time 3 group interaction. Effect size was calculated by
training group for each outcome measure (difference between
means/pooled SD). Post hoc statistical power calculations were
performed using GPower software (12). Statistical significance
was set at p # 0.05. Data analysis was performed using SPSS
(version 11.5, SPSS Inc., Chicago, Ill).
After 6 weeks of training, there were increases in vertical jump
height (F ½1, 10 = 42.22, p , 0.05, Figure 1) and decreases in
agility times (F ½1, 10 = 60.97, p , 0.05, Figure 2) for both
Figure 1. Vertical jump height (cm) separated by group pre- and
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Plyometric Training Techniques
Time to complete the 505 agility test decreased for both
groups. In contrast to straight sprinting, agility involves
greater emphasis on deceleration and subsequent reactive
coupling with acceleration (21). Leg muscle power has been
moderately correlated with agility (19,20), as has reactive
strength (33). Leg muscle power, as measured by the
vertical jump, improved for both treatment groups.
Neuromuscular adaptations related to firing frequencies
and patterns are also likely to have occurred (15). These
speculated adaptations could have improved the ability to
rapidly and forcefully switch from decelerating to accelerating movements.
The magnitude of increases in strength and power after
training has been shown to be dependent on how similar the
Figure 2. Agility time (seconds) separated by group pre- and
test is to the actual training exercise (28), reflecting the role of
learning and coordination (27). Although the participants
were experienced soccer players, their previous training did
not include any type of jump training or specific maximalgroups. There were no changes in sprint speed (F ½1, 10 =
intensity change-of-direction exercises similar to those
0.14, p . 0.05, Table 2) and no differences between the
employed in the study. Thus, it is likely that a meaningful
treatment groups at improving the variables measured.
learning effect was present. Future studies should fully
For vertical jump height, DJ training resulted in a meaninghabituate participants to the testing procedures to control for
ful effect size of 1.1. Countermovement jump training resulted
this effect.
in a moderate-high effect size of 0.7. For agility, DJ and CMJ
There were no differences in acceleration or sprint speed
training resulted in meaningful effect sizes of 1.3 and 1.5,
These findings support studies showing no
respectively. The post hoc statistical power for these analyses
in sprint speed after a plyometric program
was low to moderate (23–73%).
(13,31). Repeated ballistic exercise could potentially
improve the ability to generate explosive ground-reaction
forces (9,16). Ground-contact times in plyometric bounce
DJ and CMJ activities have been reported from 300
The results of this study show that DJ and CMJ plyometric
milliseconds (6) to , 200 milliseconds, and . 400
training can positively affect vertical jump and agility
milliseconds (34), respectively. In sprinting, ground-contact
performance in soccer players, with no significant difference
times decrease from , 200 milliseconds at acceleration to ,
between modes.
100 milliseconds at top speed (21). In terms of the velocity
Vertical jump height increased for both training groups.
specificity principle of training, it is likely that the groundThe improvement in jump height indicates that adaptations
contact times were not short enough to elicit an increased
relating to increases in leg power have occurred. The
ability to generate explosive ground-reaction forces during
adaptations to both forms of training are likely to be neural
because these predominate in the early stages of strength and
There were no differences between the DJ and CMJ groups.
power training (29) and have been shown to be the main
There were differences in effect sizes between groups,
adaptation to plyometric exercise (15).
suggesting that the two modes
of training could have different
magnitudes of effect on the
performance variables meaTABLE 2. Sprint time (seconds) separated by group pre- and posttraining.
sured. The small sample size,
DJ (n = 7)
CMJ (n = 5)
low statistical power, and short
training period restrict any conPretest
clusions; however, this area
warrants further research.
5 m (s)
1.03 6 0.06
1.05 6 0.10
1.06 6 0.07
1.07 6 0.14
10 m (s)
15 m (s)
20 m (s)
1.76 6 0.06
2.45 6 0.07
3.10 6 0.11
1.78 6 0.16
2.44 6 0.17
3.07 6 0.22
1.81 6 0.09
2.52 6 0.11
3.18 6 0.14
DJ = depth jump; CMJ = countermovement jump.
1.81 6 0.18
2.50 6 0.23
3.16 6 0.27
There were no differences between treatment groups, indicating that both forms of
training were effective. Depth
Journal of Strength and Conditioning Research
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jump training is commonly thought to be a more effective
training mode than CMJ (4,34), but no study has yet to show
greater significant improvements in leg power compared
with CMJ training (8,14,17). The results of this study
highlight the potential of using both plyometric training
techniques to improve the power-related components of
soccer thought to be necessary for success (25).
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