The Natural Developmentand Trainability ofPlyometric Ability DuringChildhoodRhodri S. Lloyd, MSc, CSCS, ASCC,1 Robert W. Meyers, MSc, ASCC,2 and Jon L. Oliver, PhD2

1Faculty of Applied Sciences, University of Gloucestershire, United Kingdom; and 2Cardiff School of Sport, Universityof Wales Institute Cardiff, United Kingdom

S U M M A R Y

THE INCLUSION OF PLYOMETRICS

WITHIN YOUTH-BASED STRENGTH

AND CONDITIONING PROGRAMS

IS BECOMING MORE POPULAR AS

A MEANS TO DEVELOP STRETCH-

SHORTENING CYCLE ABILITY.

PLYOMETRIC TRAINING ADAPTA-

TIONS HAVE PREVIOUSLY BEEN

REPORTED FOR RUNNING VELOC-

ITY, POWER, AGILITY, AND RUN-

NING ECONOMY, AND

THEREFORE, ATHLETES SHOULD

BE EXPOSED TO THIS TRAINING

MODALITY AT SOME POINT DUR-

ING 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 PROGRES-

SION MODEL BASED AROUND THE

LONG-TERM DEVELOPMENT OF

YOUNG ATHLETES.

THE SCIENCE OF PLYOMETRICS

Plyometrics refers to a trainingmodality, mainly some form ofjumping or rebounding, where

an eccentric ‘‘stretching’’ of the muscle

is rapidly terminated by a powerfulisometric contraction, thus initiatinga myotatic stretch reflex, which en-hances the subsequent concentric ac-tion (41,48). The importance ofplyometrics to a strength and condi-tioning program has previously beenestablished, with positive trainingadaptations reported for force produc-tion (32), muscular power (45), runningvelocity (23), and running economy(19). Such biomotor abilities are under-lined by a specific muscle patternknown as the stretch-shortening cycle(SSC), an intricate sequential combi-nation of eccentric, isometric, andconcentric muscle actions that pro-mote an enhanced concentric forceoutput (20). The SSC relies on elasticenergy (5) and reflex muscle activity(22) mechanisms, both of which arebelieved to develop naturally through-out childhood and are also known tobe sensitive to training.

Previously, the SSC has been catego-rized into fast and slow actions basedon a ground contact threshold of 250milliseconds (44). Fast SSC activities(,250 milliseconds) are prevalent inthe stance phase during maximalsprinting (3), whereas slow SSC actionsare evident in the performance ofmaximal vertical countermovementjumps. Although it has been suggestedthat slow SSC actions may enablegreater force production because of

increased contraction time (47), fastSSC actions promote greater move-ment speed via elastic energy usageand stretch reflex contributions (22). Itis imperative that a coach and strengthand conditioning specialist acknowl-edges the different categories of SSCactions and that athlete programs aredesigned with consideration given tothe desired training form of SSC.

One way of ensuring that the athlete isbeing exposed to the correct trainingstimuli is by monitoring the reactivestrength index (RSI), which is calcu-lated by dividing the height jumped(millimeters) by the time spent incontact with the ground developingthe required vertical forces (35). Themeasure has previously been viewedas a suitable means to prescribe andmonitor plyometric intensity, by de-termining optimal drop jump height(15,35). Increases in drop height willpromote improvements in RSI, as theSSC is sensitive to the magnitude andvelocity of the eccentric stretch (7);however, excessive increases in inten-sity may promote prolonged groundcontact times and reduced RSImeasures.

K E Y W O R D S :

long-term athlete development; reactivestrength index; stretch-shortening cycle;pediatric

Copyright � National Strength and Conditioning Association Strength and Conditioning Journal | www.nsca-lift.org 23

LONG-TERM ATHLETEDEVELOPMENT

Owing to the growing debate surround-ing the physical and physiologicaldevelopment of youths, a number oflong-term athletic development (LTAD)models have been developed in a bid tomaximize athletic potential (1,49). Suchmodels propose the existence of ‘‘win-dows of opportunity,’’ defined as uniqueperiods within a child’s developmentwhere a heightened sensitivity to train-ing adaptation is possible in response tothe correct training stimulus (1,49).Based on research that has examinedthe natural development throughoutchildhood of various physical compo-nents, such as speed (40), strength(28,50), aerobic endurance (37), andmuscular power (31), it is suggested thatthere exists two ‘‘windows of opportu-nity’’ for each characteristic (1). Thesetypically include a prepubescent win-dow incorporating age-related neuro-muscular coordination developmentsand a circa- or postpubertal windowlinked to maturity-associated increasesin muscle mass and circulating sexandrogen concentrations (49).

Although it is accepted that the use ofsuch models is better than none at all,a lack of longitudinal and empiricalresearch has ensured that questions stillremain as to the validity of suchdevelopmental pathways. Despite theexisting issues concerning LTAD mod-els, the identification of potential‘‘windows of opportunity’’ has forcedcoaches to consider their approachesto youth athletic development.

Although there is existing evidence forstrength, speed, and endurance, minimalresearch exists for plyometric develop-ment. It is suggested that the limitednumber of controlled studies that haveused plyometric training in children islargely because of the possible miscon-ceptions surrounding safety and ethicalissues. Of the available literature, im-provements resulting from plyometricprograms have been reported for re-bound jump height (36), agility andpower (45), vertical jump performance(43,11), running velocity (23), and rate offorce development (34).

Recent research has suggested theexistence of periods of naturally occur-ring accelerated adaptation betweenthe ages of 10 and 11 and between12 and 13 for RSI in children (30),suggesting potential ‘‘windows ofopportunity’’ for plyometric develop-ment. The authors did report worth-while changes between various agegroups for bilateral submaximal hop-ping, which promotes ground contacttimes indicative of fast SSC actions;however, the magnitudes of thesechanges were not deemed sufficientlylarge to assume that ‘‘periods of accel-erated adaptation’’ were evident (30).

NATURAL DEVELOPMENT OFPLYOMETRIC ABILITY

Developmental trends for slow SSCability have been reported indirectlyfrom measures of squat and counter-movement jump heights, with reportedincreases in vertical jump height aschildren become older (46,18). Im-provements in motor coordinationand more effective utilization of mus-cular power, possibly through in-creased muscle mass and rate coding,are proposed mechanisms underpin-ning such slow SSC development. FastSSC, as represented by measures of legstiffness during bilateral submaximalhopping, has also been shown toincrease with age (30); however, themechanisms for such development areless clear.

Plyometric ability is governed by effec-tive neuromuscular function, which isthe integration of both neural andmuscular systems. Structural compo-nents that are likely to affect plyomet-ric performance would include muscle-tendon size and architecture, tendonstiffness (the ability of the tendon toresist changes in length), and joint stiff-ness, defined as the ratio of the changein joint torque to joint angular displace-ment (24). Neural factors that mayimpact plyometric ability include motorunit recruitment, neural coordination(whole body, reciprocal, inter- andintramuscular), preactivation beforeground contact, and stretch reflexresponses immediately after groundcontact. Such attributes are known to

develop naturally throughout child-hood and into adulthood, with youn-ger children displaying more inhibitorymechanisms and a reduced neuromus-cular efficiency (26), greater levels ofantagonist activation immediately afterground contact (6), and lower stretchreflex responses than adults (17,38).

These studies would suggest thatwith age, muscle activation strategiestransition from reactive, protective in-hibition, to preparatory, performance-enhancing excitation. Because of thesecomponents showing evidence of nat-ural development, it seems pertinent tosuggest that they may be susceptibleto further enhancement with exposureto the appropriate training stimulus.This is evidenced by the beneficialadaptation to performance markers(10) and a reduction of sports-relatedinjuries (27,51) in a number of recentlypublished youth-based training studies.Adaptations in agility and power (45),vertical jump height (11), rate of forcedevelopment (34), rebound jumpheight (36), and running speed (23)have all been reported for youthpopulations in response to trainingprograms inclusive of plyometricexercises.

Concerns related to damage to imma-ture epiphyseal growth plates previ-ously deemed plyometrics as anunsuitable training modality for chil-dren; however, it is apparent that verylittle research is available for promotinga ‘‘cause and effect’’ relationship be-tween plyometrics and pediatric injury.The preventive measure endorsedcommonly suggesting that as a pre-requisite, children should be able tofully back squat 1.5 times their ownbody weight appears flawed, especiallywhen considering that prepubertalchildren often participate unknowinglyin low level plyometrics during theirfree play, namely, through some formof running, skipping, hopping, orjumping (10). Within such tasks, theextensors of the lower limbs areroutinely subjected to the cyclicalnature of fast SSC and arguably atlower exercise intensities than theprerequisite strength criterion would

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promote. Therefore, the primary con-cern could be one of muscle damageand soreness; however, this should beavoidable with appropriate exerciseprescription, correct supervision, andlogical training progressions.

According to the recent NationalStrength and Conditioning Association(NSCA) position statement for youthresistance training (10), individualsinstructing and supervising youth train-ing sessions should possess a level ofknowledge equal to a college degree,a recognized accredited status (e.g.,NSCA Certified Strength and Condi-tioning Specialist or the United King-dom Strength and ConditioningAssociation Accredited Strength andConditioning Coach), and practicalexperience of working with childrenof different ages (10).

IMPLICATIONS FOR PLYOMETRICTRAINING

Previous plyometric drill progressionshave been reported in the literature(40), which provide strength andconditioning coaches with a logicalapproach to plyometric development.As with any form of exercise program,the variables of intensity, volume,frequency, repetition velocity, and re-covery must be carefully monitored toensure optimal athletic developmentwhile minimizing injury risk.

TRAINING INTENSITY

The intensity of a plyometric exerciserefers to the amount of stress placed onthe musculotendinous unit and islargely dependent on exercise selection(42). When considering appropriatetraining intensities for youths, it isessential that a child begins with low-intensity drills and gradually over time,advances to higher intensity drills (8).Only after sufficient experience andrepeated demonstration of sound tech-nique, should a child advance to higherintensity plyometric exercises. As withany form of exercise prescription, it isimperative that strength and condi-tioning coaches do not simply super-impose an adult-based program onchildren and must avoid treatingchildren as ‘‘miniature adults’’ (14).

TRAINING VOLUME

Plyometric training volume has pre-viously been discussed in relation tothe total number of foot contactsperformed during a single session(16). Authors have previously sug-gested that children begin with a singleset of 6–10 repetitions, progressing upto 2–3 sets of 6–10 repetitions for bothupper- and lower-body plyometrics(9). Therefore, total ground contactsfor a child might range from 50 to 150depending on their age, level ofexperience, and the training intensity,with initial lower loads for higherintensity exercises. However, it shouldbe acknowledged that the quality ofplyometric performance is more im-portant than the total session volume.Owing to the large neural contributioninherent to plyometrics, it is suggestedthat strength and conditioning coachesmake use of thresholds of performancevariables such as ground contact timeor RSI, to determine the end of a givenset. For example, previous research hasreported mean contact times of ap-proximately 185 and 205 millisecondsfor 13-year old boys, and 190 and 230milliseconds for 16-year old males andfemales, during submaximal and max-imal hopping exercises respectively(29), and such values could be usedas �cut-off� points whereby a given setceases when contact times go abovesuch a threshold. However, it must bestressed that any performance thresh-old should be considered on an in-dividual basis depending on the initialbaseline performance of a child.

TRAINING FREQUENCY

Previous pediatric literature has pro-posed that children can perform plyo-metric exercises twice weekly onnonconsecutive days (8,9). Althoughthere is a lack of evidence delineatingan optimal training frequency, it isbetter to underestimate the child’sabilities than to provide excessivetraining exposure, which could ulti-mately lead to an overuse injury.

Children are known to experience lessmuscle damage than adults, even whenexercise intensity is controlled (33);therefore, using soreness to monitor

training is deemed inappropriate. Analternative approach to assess athletereadiness could be to acquire a measureof ground contact time or RSI duringsubmaximal hopping, which could re-veal neural fatigue without placingexcessive physical demands on thechild. Previous research has revealedthat exhaustive exercise involving SSCactions can reduce joint stiffness (25)and alter neuromuscular recruitmentstrategies (39) because of peripheraland metabolic fatigue. Consequently,the strength and conditioning coachshould be aware of any additionalphysical conditioning that the child isengaged in, as additional training out-side of the supervised program mayproduce a cumulative fatiguing effectthat may result in injury, illness, orburnout (2).

REPETITION VELOCITY

Owing to the fact that successfulplyometric performance is governedby effective SSC utilization, which inturn is mediated by both the magni-tude and velocity of stretch (4,7), it isimperative that high repetition velocityis maintained. Clear and concise in-structions should be given for anyplyometric exercise, with a clear tech-nical focus and motivational phrasing(e.g., ‘‘jump as high as possible, as fastas possible’’) to maximize repetitionvelocity. Also, intermittent feedbackfrom the strength and conditioningcoach on performance thresholds suchas contact time and RSI could increaseathlete motivation and subsequentperformance outcome (15).

Plyometrics require more intricateneural activation pathways than regu-lar resistance exercises, and it isimperative that plyometric executionis reliant on both feedforward pro-cesses from the CNS before andfeedback processes from propriocep-tors during ground contact (48). Tosatisfy this requirement and maximizetraining adaptation, the number of setsand repetitions performed should beflexible, as opposed to the quality ofrepetition velocity during ground con-tact time.

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RECOVERY

Despite the notion that children canoften recover from repeated sets ofmoderate-intensity resistance trainingwith less recovery time (13), plyomet-rics require longer rest periods toenable full neuromuscular recovery,maximize performance, and reduceinjury risk (48). During the initial stagesof the proposed model (Figure 1), restintervals can range from 1 to 3 minutes(23); however, when training intensi-ties are increased in stages 5 and 6 (inwhich athletes are entering adulthood),young athletes may require longer restperiods to enable optimal power de-velopment. It should be noted that therest required specifically by a childmight differ owing to individual vari-ation; however, at all times, coachesshould overestimate as opposed tounderestimate the necessary rest toenable full recovery and maintenanceof training intensity (8).

RECOMMENDATIONS

Although plyometric programming mustbe designed specific to an individual,

below is a summary of the proposedguidelines for youth plyometrics:

1. Training intensity: should be basedon eccentric loading, and at alltimes, children should progress fromlow-intensity to high-intensityexercises.

2. Training volume: children shoulduse performance thresholds (e.g.,ground contact time or RSI) todetermine training volume; how-ever, single sets of 6–10 repetitions,progressing to multiple sets of 6–10repetitions as a general guideline issupported.

3. Training frequency: 2 sessions perweek on nonconsecutive days.

4. Repetition velocity: use of perfor-mance thresholds (as above) tomaximize motivation and perfor-mance quality.

5. Recovery: 60–180 seconds intersetrest period for low level plyometrics;however, this may need to beincreased when performing multipleplyometrics of a high eccentricloading nature.

SUGGESTED YOUTH-BASEDPLYOMETRIC EXERCISE MODEL

Although a number of publicationshave suggested appropriate plyometricguidelines for children (9), it wasdeemed necessary to formalize a morecomprehensive progression model(Figure 1), which corresponds withdevelopmental stages aligned with theLTAD model (1). It is intended that thisprogression model will providecoaches with a more strategic ap-proach to youth plyometric programdesign. Specifically, the model is de-signed to give coaches clear and simpleguidelines to follow based on scientifictheory and evidence, without beingoverly prescriptive, thus allowingcoaches to implement the informationin a way specific to the needs ofindividual athletes.

It is important to make clear that themodel is designed for an athlete to enterthe first stage at a young age, and thatanyone entering at an older age shouldstill complete the initial phase first, witha coach ensuring that appropriate

Figure 1. Plyometric progression model.

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technical ability is demonstrated beforethe athlete progresses. The model con-tains approximated age ranges for eachgiven stage, which are indicative ofdifferent maturational rates of men and

women; however, regardless of genderor age, a child must develop mechanicallyefficient functional movement skills be-fore attempting more complex plyomet-ric drills.

The model proposes that athletesprogress from one stage to anotheronly once mastery is consistentlydisplayed at the earlier stage. Themodel supposes that exercises should

Figure 2. (A) Bodyweight squats and (B) in-line lunges.

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increase in intensity and decrease involume as children are introduced toplyometrics of increasing eccentricloading. However, owing to the po-tential variation in biological develop-ment within a specified chronologicalage group and the lack of availableresearch that distinguishes optimalplyometric training variables for youths,it must be noted that the progressionsdisplayed in the model are not implicitfor specific chronological age groupsand that strength and conditioningcoaches should use these guidelineswith an awareness of individual vari-ability in mind. It should also behighlighted that the model has beenbased on the interpretation of availablescientific research, but longitudinal em-pirical research is required to establishits efficacy and effectiveness.

STAGE 1: FUNDAMENTALMOVEMENT SKILLS

Although it has previously been sug-gested that children are able to beginplyometric training when they have theemotional maturity to listen to andfollow instructions (8), the strength andconditioning coach should be satisfied

that the child can demonstrate soundlanding mechanics and competent basicmovement patterns. Such fundamentalmovements should incorporate elementsof agility, balance, and coordination andexpose the child to an environment thatdevelops kinesthetic and spatial aware-ness. Potential exercises are largely re-stricted to the imagination of the coach;however, such movement skills couldinclude freestanding bodyweight squatsand in-line lunges (Figure 2) or similarclosed kinetic chain exercises requiringtriple extension at the ankles, knees, andhips. Where possible, these exercisesshould be incorporated into games ordeliberate play type activities, whichshould eliminate the boredom that canbe displayed by children who inherentlydislike monotonous forms of training (8).Combining plyometric drills with skill-based activities or those targeting differ-ent components of fitness should helpkeep children engaged in a trainingsession (8). Progression to stage 2 shouldonly take place when locomotive com-petence is demonstrated in fundamentalmovement skills (FMS) such as running,skipping, and hopping that requireagility, balance, and coordination (12).

STAGE 2: LOW-INTENSITYPLYOMETRICS—JUMPING

The next progression involves a rangeof jumping exercises, which require thechild to perform on the spot jumps orvertical and horizontal standing jumps.These exercises typically involve thechild jumping and landing bilaterally orunilaterally, thus highlighting the needfor satisfactory fundamental movementskill mastery. In order for a child tominimize injury and maximize plyo-metric performance, it is suggested thatthey must display correct landingmechanics, including a heel-toe land-ing, supporting flexion at the tripleextension sites, avoid excessive valgusknee displacement (Figure 3), as dem-onstrated in Figure 3, maintenanceof lumbothoracic integrity at the pointof ground contact, and coordination ofthe upper and lower limbs throughoutthe exercise.

STAGE 3: MEDIUM-INTENSITYPLYOMETRICS 1—MULTIPLEBILATERAL HOPPING ANDJUMPING

Once the young athlete can executejumping tasks proficiently, the

Figure 3. (A) Correct landing mechanics and (B) Valgus knee displacement on landing.

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Figure 4. (A) Pogo stick hopping and (B) single-leg line hopping drills.

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subsequent stage is hopping where anelement of horizontal distance is in-troduced to the plyometric task. Dur-ing this stage, children should beintroduced to ground contact on theballs of their feet, only using a heel-toefoot strike when stopping. Exerciseswithin this category might include‘‘pogo stick hopping’’ (Figure 4A) andmultiple countermovement jumps;however, where possible, multidirec-tional movements should be incorpo-rated. This developmental phase shouldensure movement characteristics indic-ative of true SSC behavior, requiring fastground contact times (,250 millisec-onds (44)), and a degree of preactiva-tion, which require the child to use theirlower limbs as ‘‘stiff springs.’’

STAGE 4: MEDIUM-INTENSITYPLYOMETRICS 2—BOX JUMPS

Once a child has demonstrated com-petence at stages 1–3 and enteredadolescence, they can move ontolow-intensity box jumps (jumping ontoand stepping down from a box),‘‘obstacle’’ drills such as the use ofhurdles, and multiple jumps. The aimof this stage is to increase eccentricloading, while maintaining both thespeed of movement learnt in medium-intensity plyometrics 1 and the tech-nical competence from the FMS andlow-intensity plyometrics stages.

STAGES 5 AND 6: HIGH-INTENSITYPLYOMETRICS

The final 2 stages are for adolescentswho are entering young adulthood.

BOUNDING. Such exercises wouldincorporate multidirectional, bilateral,or unilateral alternating foot contacts,whereby the objective is to covermaximum distance with minimalground contact time, for example,single-leg line hopping (Figure 4B). Thisphase begins to place additional ec-centric loading on the lower limbstructures and should only be intro-duced to young athletes who aredeemed able to tolerate such loadingby their coach.

DROPS. Regardless of trainingexperience, performers should beintroduced to these stages at a lowintensity (drop heights #20 cm),gradually intensifying the stretchload by increasing drop height, basedon ground contact times or RSImeasurements (35). The drop heightshould not be increased to an in-tensity that promotes an inhibitoryprotective strategy that reduces re-flex activation (21). It is suggestedthat regular monitoring of perfor-mance variables are used to ensurethat the plyometric intensity is nottoo great that a detrimental effect isexperienced by the performer by wayof increased ground contact times ordecreased flight times and RSI.

SUMMARY AND PRACTICALAPPLICATIONS

The current article has highlightedthat because of the natural adaptationof neural and muscular components,plyometric ability undergoes devel-opment throughout childhood andadolescence. Recent evidence wouldsuggest that both slow SSC and fastSSC improve with age; however,such trends are nonlinear, with thepossible existence of periods of ac-celerated adaptation. Incorporatingthe plyometric progression modeland program guidelines proposed inthe current article, strength andconditioning coaches should be ableto plan and monitor youth-basedplyometric training programs moreeffectively. This can be achieved withthe training emphasis placed strictlyon plyometric quality as opposed toplyometric quantity.

Rhodri S.

Lloyd is a SeniorLecturer andCourse Leader forthe BSc SportStrength andConditioningdegree at theUniversity ofGloucestershire.

Robert W.

Meyers is a lec-turer in Strengthand Conditioning,Rehabilitation andMassage at theUniversity ofWales InstituteCardiff.

Jon L. Oliver isa lecturer in Sportand ExercisePhysiology at theUniversity ofWales InstituteCardiff.

REFERENCES1. 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.

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.

VOLUME 33 | NUMBER 2 | APRIL 201130

Youth Plyometric Development

8. Faigenbaum, AD. Plyometrics for kids—Facts

and fallacies. Perf Train J 5: 13–16, 2006.

9. Faigenbaum AD and Chu DA. Plyometric

training for children and adolescents—

ACSM Current Comment, 2001. Available

at: www.acsm.org.

10. Faigenbaum AD, Kraemer WJ, Blimkie CJ,

Jeffreys I,MicheliLJ,NitkaM,andRowlandTW.

Youth resistance training: Updated position

statement paper from the National Strength

and Conditioning Association. J Strength

Cond Res 23: S60–S79, 2009.

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.

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. HarrisonAJandGaffneyS.Motordevelopment

andgender effects onSSCperformance. 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

enhancement during SSC-exercise. J Appl

Biomech 33: 1197–1206, 1997.

23. Kotzamanidis C. Effect of plyometric training

on running performance and vertical jumping

in prepubertal boys. J Strength Cond Res

20: 441–445, 2006.

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.

25. Kuitunen S, Avela J, Kyrolainen 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.

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 field-

based 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 pre-

and 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 Araujo D, eds.

Routledge, 2005. pp. 408–416.

36. Meylan C and Malatesta D. Effects of in-

season 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 Speed-

Endurance 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

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.

VOLUME 33 | NUMBER 2 | APRIL 201132

Youth Plyometric Development