The Natural Development and Trainability of Plyometric Ability

TAKE QUIZ
The Natural Development
and Trainability of
Plyometric Ability During
Childhood
Rhodri S. Lloyd, MSc, CSCS, ASCC,1 Robert W. Meyers, MSc, ASCC,2 and Jon L. Oliver, PhD2
Faculty of Applied Sciences, University of Gloucestershire, United Kingdom; and 2Cardiff School of Sport, University
of Wales Institute Cardiff, United Kingdom
1
SUMMARY
THE INCLUSION OF PLYOMETRICS
WITHIN YOUTH-BASED STRENGTH
AND CONDITIONING PROGRAMS
IS BECOMING MORE POPULAR AS
A MEANS TO DEVELOP STRETCHSHORTENING CYCLE ABILITY.
PLYOMETRIC TRAINING ADAPTATIONS HAVE PREVIOUSLY BEEN
REPORTED FOR RUNNING VELOCITY, POWER, AGILITY, AND RUNNING ECONOMY, AND
THEREFORE, ATHLETES SHOULD
BE EXPOSED TO THIS TRAINING
MODALITY AT SOME POINT DURING THEIR TRAINING PROGRAM.
HOWEVER, SOME UNCERTAINTY
STILL EXISTS WITH REGARD TO
PROGRAM DESIGN, ESPECIALLY
WHEN TAKING GROWTH AND
MATURATIONAL FACTORS INTO
ACCOUNT. THIS ARTICLE REVIEWS
THE CURRENT YOUTH-BASED
PLYOMETRIC LITERATURE AND
PROVIDES A TRAINING PROGRESSION MODEL BASED AROUND THE
LONG-TERM DEVELOPMENT OF
YOUNG ATHLETES.
THE SCIENCE OF PLYOMETRICS
lyometrics refers to a training
modality, mainly some form of
jumping or rebounding, where
an eccentric ‘‘stretching’’ of the muscle
P
is rapidly terminated by a powerful
isometric contraction, thus initiating
a myotatic stretch reflex, which enhances the subsequent concentric action (41,48). The importance of
plyometrics to a strength and conditioning program has previously been
established, with positive training
adaptations reported for force production (32), muscular power (45), running
velocity (23), and running economy
(19). Such biomotor abilities are underlined by a specific muscle pattern
known as the stretch-shortening cycle
(SSC), an intricate sequential combination of eccentric, isometric, and
concentric muscle actions that promote an enhanced concentric force
output (20). The SSC relies on elastic
energy (5) and reflex muscle activity
(22) mechanisms, both of which are
believed to develop naturally throughout childhood and are also known to
be sensitive to training.
Previously, the SSC has been categorized into fast and slow actions based
on a ground contact threshold of 250
milliseconds (44). Fast SSC activities
(,250 milliseconds) are prevalent in
the stance phase during maximal
sprinting (3), whereas slow SSC actions
are evident in the performance of
maximal vertical countermovement
jumps. Although it has been suggested
that slow SSC actions may enable
greater force production because of
Copyright Ó National Strength and Conditioning Association
increased contraction time (47), fast
SSC actions promote greater movement speed via elastic energy usage
and stretch reflex contributions (22). It
is imperative that a coach and strength
and conditioning specialist acknowledges the different categories of SSC
actions and that athlete programs are
designed with consideration given to
the desired training form of SSC.
One way of ensuring that the athlete is
being exposed to the correct training
stimuli is by monitoring the reactive
strength index (RSI), which is calculated by dividing the height jumped
(millimeters) by the time spent in
contact with the ground developing
the required vertical forces (35). The
measure has previously been viewed
as a suitable means to prescribe and
monitor plyometric intensity, by determining optimal drop jump height
(15,35). Increases in drop height will
promote improvements in RSI, as the
SSC is sensitive to the magnitude and
velocity of the eccentric stretch (7);
however, excessive increases in intensity may promote prolonged ground
contact times and reduced RSI
measures.
KEY WORDS:
long-term athlete development; reactive
strength index; stretch-shortening cycle;
pediatric
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Youth Plyometric Development
LONG-TERM ATHLETE
DEVELOPMENT
Owing to the growing debate surrounding the physical and physiological
development of youths, a number of
long-term athletic development (LTAD)
models have been developed in a bid to
maximize athletic potential (1,49). Such
models propose the existence of ‘‘windows of opportunity,’’ defined as unique
periods within a child’s development
where a heightened sensitivity to training adaptation is possible in response to
the correct training stimulus (1,49).
Based on research that has examined
the natural development throughout
childhood of various physical components, such as speed (40), strength
(28,50), aerobic endurance (37), and
muscular power (31), it is suggested that
there exists two ‘‘windows of opportunity’’ for each characteristic (1). These
typically include a prepubescent window incorporating age-related neuromuscular coordination developments
and a circa- or postpubertal window
linked to maturity-associated increases
in muscle mass and circulating sex
androgen concentrations (49).
Although it is accepted that the use of
such models is better than none at all,
a lack of longitudinal and empirical
research has ensured that questions still
remain as to the validity of such
developmental pathways. Despite the
existing issues concerning LTAD models, the identification of potential
‘‘windows of opportunity’’ has forced
coaches to consider their approaches
to youth athletic development.
Although there is existing evidence for
strength, speed, and endurance, minimal
research exists for plyometric development. It is suggested that the limited
number of controlled studies that have
used plyometric training in children is
largely because of the possible misconceptions surrounding safety and ethical
issues. Of the available literature, improvements resulting from plyometric
programs have been reported for rebound jump height (36), agility and
power (45), vertical jump performance
(43,11), running velocity (23), and rate of
force development (34).
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VOLUME 33 | NUMBER 2 | APRIL 2011
Recent research has suggested the
existence of periods of naturally occurring accelerated adaptation between
the ages of 10 and 11 and between
12 and 13 for RSI in children (30),
suggesting potential ‘‘windows of
opportunity’’ for plyometric development. The authors did report worthwhile changes between various age
groups for bilateral submaximal hopping, which promotes ground contact
times indicative of fast SSC actions;
however, the magnitudes of these
changes were not deemed sufficiently
large to assume that ‘‘periods of accelerated adaptation’’ were evident (30).
NATURAL DEVELOPMENT OF
PLYOMETRIC ABILITY
Developmental trends for slow SSC
ability have been reported indirectly
from measures of squat and countermovement jump heights, with reported
increases in vertical jump height as
children become older (46,18). Improvements in motor coordination
and more effective utilization of muscular power, possibly through increased muscle mass and rate coding,
are proposed mechanisms underpinning such slow SSC development. Fast
SSC, as represented by measures of leg
stiffness during bilateral submaximal
hopping, has also been shown to
increase with age (30); however, the
mechanisms for such development are
less clear.
Plyometric ability is governed by effective neuromuscular function, which is
the integration of both neural and
muscular systems. Structural components that are likely to affect plyometric performance would include muscletendon size and architecture, tendon
stiffness (the ability of the tendon to
resist changes in length), and joint stiffness, defined as the ratio of the change
in joint torque to joint angular displacement (24). Neural factors that may
impact plyometric ability include motor
unit recruitment, neural coordination
(whole body, reciprocal, inter- and
intramuscular), preactivation before
ground contact, and stretch reflex
responses immediately after ground
contact. Such attributes are known to
develop naturally throughout childhood and into adulthood, with younger children displaying more inhibitory
mechanisms and a reduced neuromuscular efficiency (26), greater levels of
antagonist activation immediately after
ground contact (6), and lower stretch
reflex responses than adults (17,38).
These studies would suggest that
with age, muscle activation strategies
transition from reactive, protective inhibition, to preparatory, performanceenhancing excitation. Because of these
components showing evidence of natural development, it seems pertinent to
suggest that they may be susceptible
to further enhancement with exposure
to the appropriate training stimulus.
This is evidenced by the beneficial
adaptation to performance markers
(10) and a reduction of sports-related
injuries (27,51) in a number of recently
published youth-based training studies.
Adaptations in agility and power (45),
vertical jump height (11), rate of force
development (34), rebound jump
height (36), and running speed (23)
have all been reported for youth
populations in response to training
programs inclusive of plyometric
exercises.
Concerns related to damage to immature epiphyseal growth plates previously deemed plyometrics as an
unsuitable training modality for children; however, it is apparent that very
little research is available for promoting
a ‘‘cause and effect’’ relationship between plyometrics and pediatric injury.
The preventive measure endorsed
commonly suggesting that as a prerequisite, children should be able to
fully back squat 1.5 times their own
body weight appears flawed, especially
when considering that prepubertal
children often participate unknowingly
in low level plyometrics during their
free play, namely, through some form
of running, skipping, hopping, or
jumping (10). Within such tasks, the
extensors of the lower limbs are
routinely subjected to the cyclical
nature of fast SSC and arguably at
lower exercise intensities than the
prerequisite strength criterion would
promote. Therefore, the primary concern could be one of muscle damage
and soreness; however, this should be
avoidable with appropriate exercise
prescription, correct supervision, and
logical training progressions.
According to the recent National
Strength and Conditioning Association
(NSCA) position statement for youth
resistance training (10), individuals
instructing and supervising youth training sessions should possess a level of
knowledge equal to a college degree,
a recognized accredited status (e.g.,
NSCA Certified Strength and Conditioning Specialist or the United Kingdom Strength and Conditioning
Association Accredited Strength and
Conditioning Coach), and practical
experience of working with children
of different ages (10).
IMPLICATIONS FOR PLYOMETRIC
TRAINING
Previous plyometric drill progressions
have been reported in the literature
(40), which provide strength and
conditioning coaches with a logical
approach to plyometric development.
As with any form of exercise program,
the variables of intensity, volume,
frequency, repetition velocity, and recovery must be carefully monitored to
ensure optimal athletic development
while minimizing injury risk.
TRAINING INTENSITY
The intensity of a plyometric exercise
refers to the amount of stress placed on
the musculotendinous unit and is
largely dependent on exercise selection
(42). When considering appropriate
training intensities for youths, it is
essential that a child begins with lowintensity drills and gradually over time,
advances to higher intensity drills (8).
Only after sufficient experience and
repeated demonstration of sound technique, should a child advance to higher
intensity plyometric exercises. As with
any form of exercise prescription, it is
imperative that strength and conditioning coaches do not simply superimpose an adult-based program on
children and must avoid treating
children as ‘‘miniature adults’’ (14).
TRAINING VOLUME
Plyometric training volume has previously been discussed in relation to
the total number of foot contacts
performed during a single session
(16). Authors have previously suggested that children begin with a single
set of 6–10 repetitions, progressing up
to 2–3 sets of 6–10 repetitions for both
upper- and lower-body plyometrics
(9). Therefore, total ground contacts
for a child might range from 50 to 150
depending on their age, level of
experience, and the training intensity,
with initial lower loads for higher
intensity exercises. However, it should
be acknowledged that the quality of
plyometric performance is more important than the total session volume.
Owing to the large neural contribution
inherent to plyometrics, it is suggested
that strength and conditioning coaches
make use of thresholds of performance
variables such as ground contact time
or RSI, to determine the end of a given
set. For example, previous research has
reported mean contact times of approximately 185 and 205 milliseconds
for 13-year old boys, and 190 and 230
milliseconds for 16-year old males and
females, during submaximal and maximal hopping exercises respectively
(29), and such values could be used
as Ôcut-offÕ points whereby a given set
ceases when contact times go above
such a threshold. However, it must be
stressed that any performance threshold should be considered on an individual basis depending on the initial
baseline performance of a child.
TRAINING FREQUENCY
Previous pediatric literature has proposed that children can perform plyometric exercises twice weekly on
nonconsecutive days (8,9). Although
there is a lack of evidence delineating
an optimal training frequency, it is
better to underestimate the child’s
abilities than to provide excessive
training exposure, which could ultimately lead to an overuse injury.
Children are known to experience less
muscle damage than adults, even when
exercise intensity is controlled (33);
therefore, using soreness to monitor
training is deemed inappropriate. An
alternative approach to assess athlete
readiness could be to acquire a measure
of ground contact time or RSI during
submaximal hopping, which could reveal neural fatigue without placing
excessive physical demands on the
child. Previous research has revealed
that exhaustive exercise involving SSC
actions can reduce joint stiffness (25)
and alter neuromuscular recruitment
strategies (39) because of peripheral
and metabolic fatigue. Consequently,
the strength and conditioning coach
should be aware of any additional
physical conditioning that the child is
engaged in, as additional training outside of the supervised program may
produce a cumulative fatiguing effect
that may result in injury, illness, or
burnout (2).
REPETITION VELOCITY
Owing to the fact that successful
plyometric performance is governed
by effective SSC utilization, which in
turn is mediated by both the magnitude and velocity of stretch (4,7), it is
imperative that high repetition velocity
is maintained. Clear and concise instructions should be given for any
plyometric exercise, with a clear technical focus and motivational phrasing
(e.g., ‘‘jump as high as possible, as fast
as possible’’) to maximize repetition
velocity. Also, intermittent feedback
from the strength and conditioning
coach on performance thresholds such
as contact time and RSI could increase
athlete motivation and subsequent
performance outcome (15).
Plyometrics require more intricate
neural activation pathways than regular resistance exercises, and it is
imperative that plyometric execution
is reliant on both feedforward processes from the CNS before and
feedback processes from proprioceptors during ground contact (48). To
satisfy this requirement and maximize
training adaptation, the number of sets
and repetitions performed should be
flexible, as opposed to the quality of
repetition velocity during ground contact time.
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Youth Plyometric Development
RECOVERY
Despite the notion that children can
often recover from repeated sets of
moderate-intensity resistance training
with less recovery time (13), plyometrics require longer rest periods to
enable full neuromuscular recovery,
maximize performance, and reduce
injury risk (48). During the initial stages
of the proposed model (Figure 1), rest
intervals can range from 1 to 3 minutes
(23); however, when training intensities are increased in stages 5 and 6 (in
which athletes are entering adulthood),
young athletes may require longer rest
periods to enable optimal power development. It should be noted that the
rest required specifically by a child
might differ owing to individual variation; however, at all times, coaches
should overestimate as opposed to
underestimate the necessary rest to
enable full recovery and maintenance
of training intensity (8).
RECOMMENDATIONS
Although plyometric programming must
be designed specific to an individual,
Figure 1. Plyometric progression model.
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VOLUME 33 | NUMBER 2 | APRIL 2011
below is a summary of the proposed
guidelines for youth plyometrics:
1. Training intensity: should be based
on eccentric loading, and at all
times, children should progress from
low-intensity to high-intensity
exercises.
2. Training volume: children should
use performance thresholds (e.g.,
ground contact time or RSI) to
determine training volume; however, single sets of 6–10 repetitions,
progressing to multiple sets of 6–10
repetitions as a general guideline is
supported.
3. Training frequency: 2 sessions per
week on nonconsecutive days.
4. Repetition velocity: use of performance thresholds (as above) to
maximize motivation and performance quality.
5. Recovery: 60–180 seconds interset
rest period for low level plyometrics;
however, this may need to be
increased when performing multiple
plyometrics of a high eccentric
loading nature.
SUGGESTED YOUTH-BASED
PLYOMETRIC EXERCISE MODEL
Although a number of publications
have suggested appropriate plyometric
guidelines for children (9), it was
deemed necessary to formalize a more
comprehensive progression model
(Figure 1), which corresponds with
developmental stages aligned with the
LTAD model (1). It is intended that this
progression model will provide
coaches with a more strategic approach to youth plyometric program
design. Specifically, the model is designed to give coaches clear and simple
guidelines to follow based on scientific
theory and evidence, without being
overly prescriptive, thus allowing
coaches to implement the information
in a way specific to the needs of
individual athletes.
It is important to make clear that the
model is designed for an athlete to enter
the first stage at a young age, and that
anyone entering at an older age should
still complete the initial phase first, with
a coach ensuring that appropriate
Figure 2. (A) Bodyweight squats and (B) in-line lunges.
technical ability is demonstrated before
the athlete progresses. The model contains approximated age ranges for each
given stage, which are indicative of
different maturational rates of men and
women; however, regardless of gender
or age, a child must develop mechanically
efficient functional movement skills before attempting more complex plyometric drills.
The model proposes that athletes
progress from one stage to another
only once mastery is consistently
displayed at the earlier stage. The
model supposes that exercises should
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Youth Plyometric Development
Figure 3. (A) Correct landing mechanics and (B) Valgus knee displacement on landing.
increase in intensity and decrease in
volume as children are introduced to
plyometrics of increasing eccentric
loading. However, owing to the potential variation in biological development within a specified chronological
age group and the lack of available
research that distinguishes optimal
plyometric training variables for youths,
it must be noted that the progressions
displayed in the model are not implicit
for specific chronological age groups
and that strength and conditioning
coaches should use these guidelines
with an awareness of individual variability in mind. It should also be
highlighted that the model has been
based on the interpretation of available
scientific research, but longitudinal empirical research is required to establish
its efficacy and effectiveness.
STAGE 1: FUNDAMENTAL
MOVEMENT SKILLS
Although it has previously been suggested that children are able to begin
plyometric training when they have the
emotional maturity to listen to and
follow instructions (8), the strength and
conditioning coach should be satisfied
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VOLUME 33 | NUMBER 2 | APRIL 2011
that the child can demonstrate sound
landing mechanics and competent basic
movement patterns. Such fundamental
movements should incorporate elements
of agility, balance, and coordination and
expose the child to an environment that
develops kinesthetic and spatial awareness. Potential exercises are largely restricted to the imagination of the coach;
however, such movement skills could
include freestanding bodyweight squats
and in-line lunges (Figure 2) or similar
closed kinetic chain exercises requiring
triple extension at the ankles, knees, and
hips. Where possible, these exercises
should be incorporated into games or
deliberate play type activities, which
should eliminate the boredom that can
be displayed by children who inherently
dislike monotonous forms of training (8).
Combining plyometric drills with skillbased activities or those targeting different components of fitness should help
keep children engaged in a training
session (8). Progression to stage 2 should
only take place when locomotive competence is demonstrated in fundamental
movement skills (FMS) such as running,
skipping, and hopping that require
agility, balance, and coordination (12).
STAGE 2: LOW-INTENSITY
PLYOMETRICS—JUMPING
The next progression involves a range
of jumping exercises, which require the
child to perform on the spot jumps or
vertical and horizontal standing jumps.
These exercises typically involve the
child jumping and landing bilaterally or
unilaterally, thus highlighting the need
for satisfactory fundamental movement
skill mastery. In order for a child to
minimize injury and maximize plyometric performance, it is suggested that
they must display correct landing
mechanics, including a heel-toe landing, supporting flexion at the triple
extension sites, avoid excessive valgus
knee displacement (Figure 3), as demonstrated in Figure 3, maintenance
of lumbothoracic integrity at the point
of ground contact, and coordination of
the upper and lower limbs throughout
the exercise.
STAGE 3: MEDIUM-INTENSITY
PLYOMETRICS 1—MULTIPLE
BILATERAL HOPPING AND
JUMPING
Once the young athlete can execute
jumping tasks proficiently, the
Figure 4. (A) Pogo stick hopping and (B) single-leg line hopping drills.
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Youth Plyometric Development
subsequent stage is hopping where an
element of horizontal distance is introduced to the plyometric task. During this stage, children should be
introduced to ground contact on the
balls of their feet, only using a heel-toe
foot strike when stopping. Exercises
within this category might include
‘‘pogo stick hopping’’ (Figure 4A) and
multiple countermovement jumps;
however, where possible, multidirectional movements should be incorporated. This developmental phase should
ensure movement characteristics indicative of true SSC behavior, requiring fast
ground contact times (,250 milliseconds (44)), and a degree of preactivation, which require the child to use their
lower limbs as ‘‘stiff springs.’’
DROPS. Regardless of training
experience, performers should be
introduced to these stages at a low
intensity (drop heights #20 cm),
gradually intensifying the stretch
load by increasing drop height, based
on ground contact times or RSI
measurements (35). The drop height
should not be increased to an intensity that promotes an inhibitory
protective strategy that reduces reflex activation (21). It is suggested
that regular monitoring of performance variables are used to ensure
that the plyometric intensity is not
too great that a detrimental effect is
experienced by the performer by way
of increased ground contact times or
decreased flight times and RSI.
STAGE 4: MEDIUM-INTENSITY
PLYOMETRICS 2—BOX JUMPS
SUMMARY AND PRACTICAL
APPLICATIONS
Once a child has demonstrated competence at stages 1–3 and entered
adolescence, they can move onto
low-intensity box jumps (jumping onto
and stepping down from a box),
‘‘obstacle’’ drills such as the use of
hurdles, and multiple jumps. The aim
of this stage is to increase eccentric
loading, while maintaining both the
speed of movement learnt in mediumintensity plyometrics 1 and the technical competence from the FMS and
low-intensity plyometrics stages.
The current article has highlighted
that because of the natural adaptation
of neural and muscular components,
plyometric ability undergoes development throughout childhood and
adolescence. Recent evidence would
suggest that both slow SSC and fast
SSC improve with age; however,
such trends are nonlinear, with the
possible existence of periods of accelerated adaptation. Incorporating
the plyometric progression model
and program guidelines proposed in
the current article, strength and
conditioning coaches should be able
to plan and monitor youth-based
plyometric training programs more
effectively. This can be achieved with
the training emphasis placed strictly
on plyometric quality as opposed to
plyometric quantity.
STAGES 5 AND 6: HIGH-INTENSITY
PLYOMETRICS
The final 2 stages are for adolescents
who are entering young adulthood.
BOUNDING. Such exercises would
incorporate multidirectional, bilateral,
or unilateral alternating foot contacts,
whereby the objective is to cover
maximum distance with minimal
ground contact time, for example,
single-leg line hopping (Figure 4B). This
phase begins to place additional eccentric loading on the lower limb
structures and should only be introduced to young athletes who are
deemed able to tolerate such loading
by their coach.
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VOLUME 33 | NUMBER 2 | APRIL 2011
Robert W.
Meyers is a lecturer in Strength
and Conditioning,
Rehabilitation and
Massage at the
University of
Wales Institute
Cardiff.
Jon L. Oliver is
a lecturer in Sport
and Exercise
Physiology at the
University of
Wales Institute
Cardiff.
REFERENCES
1. Balyi I and Hamilton A. Long-Term Athlete
Development: Trainability in Childhood
and Adolescence—Windows of
Opportunity—Optimal Trainability. Victoria,
Australia: National Coaching Institute
British Columbia & Advanced Training and
Performance Ltd, 2004.
2. Brenner J and Council on Sports Medicine
and Fitness. Overuse injuries, overtraining,
and burnout in children and adolescent
athletes. Pediatrics 119: 1242–1245, 2007.
3. Bret C, Rahmani A, Dufour A-B,
Messonnier L, and Lacour J-R. Leg strength
and stiffness as ability factors in 100 m
sprint running. J Sports Med Phys Fitness
42: 274–281, 2002.
4. Butler RJ, Crowell HP, and Davis IM. Lower
extremity stiffness: Implications for
performance and injury. Clin Biomech 18:
511–517, 2003.
5. Cavagna GA, Dusman B, and Margaria R.
Positive work done by a previously stretched
muscle. J Appl Physiol 24: 21–32, 1968.
Rhodri S.
Lloyd is a Senior
Lecturer and
Course Leader for
the BSc Sport
Strength and
Conditioning
degree at the
University of
Gloucestershire.
6. Croce RV, Russell PJ, Swartz EE, and
Decoster LC. Knee muscular response
strategies differ by developmental level but
not gender during jump landing.
Electromyogr Clin Neurophysiol 44:
339–348, 2004.
7. Cronin JB, McNair PJ, and Marshall RN.
Power absorption and production during
slow, large-amplitude stretch-shorten cycle
motions. Eur J Appl Physiol 87: 59–65,
2002.
8. Faigenbaum, AD. Plyometrics for kids—Facts
and fallacies. Perf Train J 5: 13–16, 2006.
enhancement during SSC-exercise. J Appl
Biomech 33: 1197–1206, 1997.
9. Faigenbaum AD and Chu DA. Plyometric
training for children and adolescents—
ACSM Current Comment, 2001. Available
at: www.acsm.org.
23. Kotzamanidis C. Effect of plyometric training
on running performance and vertical jumping
in prepubertal boys. J Strength Cond Res
20: 441–445, 2006.
10. Faigenbaum AD, Kraemer WJ, Blimkie CJ,
Jeffreys I, Micheli LJ, Nitka M, and Rowland TW.
Youth resistance training: Updated position
statement paper from the National Strength
and Conditioning Association. J Strength
Cond Res 23: S60–S79, 2009.
24. Kubo K, Morimoto M, Komuro T, Tsunoda N,
Kanehisa H, and Fukunaga T. Influences of
tendon stiffness, joint stiffness, and
electromyographic activity on jump
performance using single joint. Eur J Appl
Physiol 99: 235–243, 2007.
11. Faigenbaum AD, McFarland JE, Keiper FB,
Tevlin W, Ratamess NA, Kang J, and
Hoffman JR. Effects of a short-term
plyometric and resistance training program
on fitness in boys age 12 to 15 years.
J Sports Sci Med 6: 519–525, 2007.
25. Kuitunen S, Avela J, Kyröläinen H, Nicol C,
and Komi PV. Acute and prolonged reduction
in joint stiffness in humans after exhausting
stretch-shortening cycle exercise. Eur J Appl
Physiol 88: 107–116, 2002.
12. Faigenbaum AD and Meadors L. A coaches
dozen: 12 FUNdamental principles for
building young and healthy athletes.
Strength Cond J 32: 99–101, 2010.
13. Faigenbaum A, Ratamess N, McFarland J,
Kaczmarek J, Coraggio M, Kang J, and
Hoffman J. Effect of rest interval length on
bench press performance in boys, teens and
men. Pediatr Exerc Sci 20: 457–469, 2008.
14. Faigenbaum AD and Westcott WL. Youth
Strength Training. Champaign, IL: Human
Kinetics, 2009. pp. 3–16.
15. Flanagan EP and Comyns TM. The use of
contact time and the reactive strength
index to optimize fast SSC training.
Strength Cond J 30: 32–38, 2008.
16. Gambetta V. Athletic Development.
Champaign, IL: Human Kinetics, 2007.
pp. 209–227.
17. Grosset JF, Mora I, Lambertz D, and Perot C.
Changes in stretch-reflexes and muscle
stiffness with age in prepubescent children.
J Appl Physiol 102: 2352–2360, 2007.
18. Harrison AJ and Gaffney S. Motor development
and gender effects on SSC performance. J Sci
Med Sport 4: 406–415, 2001.
19. Kerdok AE, Biewener AA, McMahon TA,
Weyand PG, and Herr HM. Energetics and
mechanics of human running on surfaces of
different stiffnesses. J Appl Physiol 92:
469–478, 2002.
20. Komi PV. Training of muscle strength and
power: interaction of neuromotoric,
hypertrophic, and mechanical factors. Int J
Sports Med 7: 10–15, 1986.
21. Komi PV. Stretch-shortening cycle. In:
Strength and Power in Sport. Komi PV, ed.
Oxford, England: Blackwell Scientific
Publications, 2003. pp. 184–202.
22. Komi PV and Gollhoffer A. Stretch reflex
can have an important role in force
26. Lambertz D, Mora I, Grosset JF, and
Perot C. Evaluation of musculotendinous
stiffness in prepubertal children and adults,
taking into account muscle activity. J Appl
Physiol 95: 64–72, 2003.
27. Lephart S, Abt J, Ferris C, Sell T, Nagai T,
Myers J, and Irrgang J. Neuromuscular and
biomechanical characteristic changes in
high school athletes: A plyometric versus
basic resistance program. Br J Sports Med
39: 932–938, 2005.
28. Lillegard WA, Brown EW, Wilson DJ,
Henderson R, and Lewis E. Efficacy of
strength training in pre-pubescent to early
postpubescent males and females: Effects
of gender and maturation. Ped Rehab 1:
147–157, 1997.
29. Lloyd RS, Oliver JL, Hughes MG, and
Williams CA. Reliability and validity of fieldbased measures of leg stiffness and
reactive strength index in youths. J Sports
Sci 27: 1565–1575, 2009.
30. Lloyd RS, Oliver JL, Hughes MG, and
Williams CA. The influence of chronological
age on periods of accelerated adaptation of
stretch-shortening cycle performance in preand post-pubescent boys. J Strength Cond
Res. doi: 10.1519/JSC.0b013e3181e7faa8.
31. Malina RM, Eisenmann JC, Cumming SP,
Ribiero B, and Aroso J. Maturity-associated
variation in the growth and functional
capacities of youth football (soccer)
players 13-15 years. Eur J Appl Physiol 91:
555–562, 2004.
32. Malisoux L, Francaux M, Nielens H, and
Theisen D. Stretch-shortening cycle
exercises: An effective training paradigm to
enhance power output of human single
muscle fibers. J Appl Physiol 100: 771–
779, 2006.
33. Marginson V, Rowlands AV, Gleeson NP,
and Eston RG. Comparison of the symptoms
of exercise-induced muscle damage after an
initial and repeated bout of plyometric
exercise in men and boys. J Appl Physiol
99: 1174–1181, 2005.
34. Matavulj D, Kukolj M, Ugarkovic D, Tihanyi J,
and Jaric S. Effects of plyometric training on
jumping performance in junior basketball
players. J Sports Med Phys Fitness 41:
159–164, 2001.
35. McClymont D. Use of the reactive strength
index (RSI) as an indicator of plyometric
training conditions. In: Science and Football V:
The Proceedings of the 5th World Congress
on Science and Football, Part VI—Football
Training. Reily T, Cabri J, and Araújo D, eds.
Routledge, 2005. pp. 408–416.
36. Meylan C and Malatesta D. Effects of inseason plyometric training within soccer
practice on explosive actions of young
players. J Strength Cond Res 23:
2605–2613, 2009.
37. Naughton G, Farpou-Lambert NJ,
Carlson J, Bradney M, and Van Praagh E.
Physiological issues surrounding the
performance of adolescent athletes.
Sports Med 30: 309–325, 2000.
38. Oliver JL and Smith PM. Neural control of leg
stiffness during hopping in boys and men.
J Electromyogr Kinesiol 20: 973–979, 2010.
39. Padua DA, Arnold BL, Perrin DH,
Gansneders BM, Carcia CR, and
Granata KP. Fatigue, vertical leg
stiffness, and stiffness control strategies
in males and females. J Athl Train 41:
294–304, 2006.
40. Philippaerts RM, Vaeyens R, Janssens M,
Van Renterghem B, Matthys D, Craen R,
Bourgois J, Vrijens J, Beunen GP, and
Malina RM. The relationship between peak
height velocity and physical performance in
youth soccer players. J Sports Sci 24:
221–230, 2006.
41. Plisk SS. Speed, Agility and SpeedEndurance Development.Agility and
Speed-Endurance Development.
In: Essentials of Strength Training and
Conditioning. Baechle TR and Earle RW,
eds. Champaign, IL: Human Kinetics,
2008. pp. 457–485.
42. Potach DH and Chu DA. Plyometritc
Training. In: Essentials of Strength Training
and Conditioning. Baechle TR and Earle
RW, eds. Champaign, IL: Human Kinetics,
2008. pp. 413–456.
43. Sankey SP, Jones PA, and Bampouras TM.
Effects of two plyometric training
programmes of different intensity on
vertical jump performance in high school
athletes. Serb J Sports Sci 2: 123–130,
2008.
Strength and Conditioning Journal | www.nsca-lift.org
31
Youth Plyometric Development
44. Schmidtbleicher D. Training for power
events. In: Strength and Power in
Sport. Komi PV, ed. Oxford, England:
Blackwell Scientific Publications, 1992.
pp. 381–395.
45. Thomas K, French D, and Hayes PR. The
effect of plyometric training techniques
on muscular power and agility in youth
soccer players. J Strength Cond Res 23:
332–335, 2009.
46. Vaeyens R, Malina RM, Janssens M,
Van Renterghem B, Bourgois J, Vrijens J
and Philippaerts RM. A multidisciplinary
selection model for youth soccer:
The Ghent Youth Soccer Project.
Br J Sports Med 40: 928–934,
2006.
47. Van Ingen Schenau GJ, Bobbert MF, and
de Haan A. Mechanics and energetics of
the stretch-shortening cycle: A stimulating
discussion. J Appl Biomech 13: 484–496,
1997.
48. Verkhoshansky Y. Supertraining (6th ed).
Rome, Italy: Verkhoshansky, 2009. pp.
267–268.
49. Viru A, Loko J, Harro M, Volver A,
Laaneaots L, and Viru M. Critical periods in
the development of performance capacity
during childhood and adolescence. Eur J
Phys Educ 4: 75–119, 1999.
50. Vrijens J. Muscle strength development in the
pre- and post-pubescent age. In: Medicine
and Sport Science: Pediatric Work
Physiology. Borms J and Hebbelinck M, eds.
New York, NY: Karger, 1978. pp. 152–158.
51. Wedderkopp N, Kaltoft B, Holm R, and
Froberg K. Comparison of two intervention
programmes in young female players in
European handball: With and without ankle
disc. Scand J Med Sci Sports 13:
371–375, 2003.
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VOLUME 33 | NUMBER 2 | APRIL 2011