Available online at www.sciencedirect.com

Journal of Science and Medicine in Sport 13 (2010) 513522

Review

Does plyometric training improve strength pe

Abstract

Majorityor slow veloof 31 effectcriteria for thand reliablethe trainingalso men ob10 weeks anwere the strategies that seem to maximize the probability to obtain significantly greater improvements in performance (p < 0.05). In orderto optimise strength enhancement, the combination of different types of plyometrics with weight-training would be recommended, ratherthan utilizing only one form (p < 0.05). The responses identified in this analysis are essential and should be considered by the strength andconditioning professional with regard to the most appropriate doseresponse trends for PT to optimise strength gains. 2009 Spo

Keywords: Fo

Contents

1. Introd2. Meth3. Statis4. Resul5. Discu6. Conc

PractRefer

1. Introdu

Musculaelements ffor carryin

CorresponE-mail ad

1440-2440/$doi:10.1016/jrts Medicine Australia. Published by Elsevier Ltd. All rights reserved.

rce; Effect size; Lower limb; Training volume; Intensity

uction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 513ods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 514tical analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 516ts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 517ssion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 517lusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 520ical implications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 520ences . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 520

ction

r strength and power are considered as criticalor a successful athletic performance, as well asg out daily activities and occupational tasks.1,2

ding author.dress: esaesae@upo.es (E. Sez-Sez de Villarreal).

Much research has been focused on the development ofmaximal strength performance as this neuromuscular qualityappears to underpin most other domains of human physi-cal capacity. Although various training methods, includingweight-training,3,4 explosive and ballistic-type resistancetraining methods,5 electrostimulation training,6,7 and vibra-tion training8 have been effectively used for the enhancementof strength performance, there is solid research evidence that

see front matter 2009 Sports Medicine Australia. Published by Elsevier Ltd. All rights reserved..jsams.2009.08.005Eduardo Sez-Sez de Villarreal a,, Bernardo Requena a, Robert U. Newton ba University Pablo de Olavide, Department of Sports, Laboratory of Human Performance, Sevilla, Spain

b Edith Cowan University, School of Exercise, Biomedical and Health Sciences, Joondalup, AustraliaReceived 28 May 2009; received in revised form 4 August 2009; accepted 12 August 2009

of the research suggests plyometric training (PT) improves maximal strength performance as measured by 1RM, isometric MVCcity isokinetic testing. However, the effectiveness of PT depends upon various factors. A meta-analysis of 15 studies with a totalsizes (ES) was carried out to analyse the role of various factors on the effects of PT on strength performance. The inclusione analysis were: (a) studies using PT programs for lower limb muscles; (b) studies employing true experimental design and validmeasurements; (c) studies including sufficient data to calculate ES. When subjects can adequately follow plyometric exercises,gains are independent of fitness level. Subjects in either good or poor physical condition, benefit equally from plyometric work,tain similar strength results to women following PT. In relation to the variables of program design, training volume of less thand with more than 15 sessions, as well as the implementation of high-intensity programs, with more than 40 jumps per session,rformance? A meta-analysis

514 E. Sez-Sez de Villarreal et al. / Journal of Science and Medicine in Sport 13 (2010) 513522

plyometric training (PT) is also effective for improving bal-listic and maximal strength.913

Plyometrics refers to exercises that are designed toenhance neinvolves apPlyometricmovements(i.e., such ametric exeron the purric exercisedrop jumpcan either bapplied indformed at vdouble-legthe lower bformance osuch as DJ,stretch-shocises are cha rapid strlowed imm(concentric

Researccoordinatioies on PTstrength,91cises suchweights anto the enharapidly incrate of forcof authorsPT on maxmodalitiesric trainingoptimisingof trainingresistancea single mtraining pro

The effious subjegender,39 aometric travariables iing resultseffectiveneume. Reseaduration, itherefore, timum enha

Despitemining theinconclusiv

ments of a PT program with regard to their effectiveness canbe achieved with the use of meta-analysis: a method thatovercomes the problems both of small sample size and low

tical phich ilem ar-analy

alson strenunt fo

treates.4,9,1e influa me

ethod

searc

Frencjump

trainininemedatab

MedLant jocondushedon heactionsesearcs werer-limbal of 2e nex

nal vaby C

ving audies

4) studes werns (Tach sturs usinumbindep: (1)s), bop sizeity; (2

ith oetric

bles iion, df exererciseuromuscular performance. For the lower body thisplication of jump, hopping and bounding training.exercises constitute a natural part of most sportas they involve jumping, hopping and skipping

s high jumping, throwing or kicking).1416 Plyo-cises are implemented in various forms dependingpose of the training program. Typical plyomet-s include the countermovement jump (CMJ), the(DJ) and the squat jump (SJ). These exercisese combined within a training program or can be

ependently. Furthermore, plyometrics can be per-arious intensity levels, ranging from low-intensityhops to high-intensity unilateral drills. As far asody is concerned, plyometrics includes the per-f various types of body-weight jumping exercises,CMJ, alternate-leg bounding, hopping, and other

rtening cycle (SSC) exercises.1720 These exer-aracterised by SSC actions, that is, they start withetch of a muscle (eccentric phase) and are fol-ediately by a rapid shortening of the same musclephase).17,19,2023

h indicates PT improves strength, power output,n, and athletic performance.2428 Numerous stud-have demonstrated improvements in maximal3,29 ranging from 11 kg to 60 kg (performing exer-as DJ, CMJ, SJ, combined jumps or combinedd plyometric training) that could be attributednced coordination and the individuals ability torease muscle tension resulting in greater maximale development (RFD).11,37 In addition, a numberdetermined24,3035 significant positive effects ofimal strength when compared with other training(i.e., weight-training, eccentric training, isomet-). However, several authors have shown that formaximal strength enhancement, the combinationmodalities (i.e., plyometrics and high-intensity

training) is recommended rather than using onlyodality.9,12,16 However, the characteristics of agram that achieves better gains are not clear.

ects of PT may differ depending on the var-ct characteristics, such as training level,3638ge,4042 sport activity or familiarity with ply-ining.11,29 Research studies that combine thesen different ways sometimes lead to conflict-.7,12,43 Other factors that seem to determine thess of PT are program duration and training vol-rch studies have used numerous combinations of

ntensity and volume characteristics4,10,12,13,44,45he optimal combination of these factors for max-ncement remains unclear.the advantages of PT, the principal issue of deter-optimal elements of a plyometric program remainse. Identification of the role of the various ele-

statisin wprobmetait canPT oacco

ity instudiine thusing

2. M

Aanddepthrics,entrain thehost,relevwere

publidatarestri

RlimbuppeA tot

Thintertionsinvol(3) stity, (studiditio

Eatigatohighness,

areas

(yeargrouactivtion wplyomvariaduratber oof exower. Meta-analysis is a quantitative approachndividual study findings addressing a commone statistically integrated and analysed.46 Becausesis can effectively increase the overall sample size,provide a more precise estimate of the effect ofgth performance. In addition, meta-analysis can

r the factors partly responsible for the variabil-ment effects observed among different training113 Thus, the purpose of this study was to exam-ence of various factors on the effectiveness of PT

ta-analysis approach.

s

h was performed using key words in the Englishh languages (e.g., jump training, drop jump,, stretch-shortening cycle, plyometric, plyomet-g of power, plyometric training, pliometrique, andnt pliometrique). These key words were appliedases ADONIS, ERIC, SPORTSDiscus, EBSCO-ine and PubMed. Moreover, manual searches of

urnals and reference lists obtained from articlescted. The present meta-analysis includes studies

in journals that have presented original researchlthy human subjects. No age, gender or languagewere imposed during the search stage.

h studies implementing PT programs for lower-used. Investigations involving training of the

s as well as summaries or abstracts were rejected.5 studies were initially identified.t step was to select studies with respect to theirlidity. Selection was based on the recommenda-ampbell and Stanley47 and included; (1) studies

control group, (2) randomised control studies,using instruments with high reliability and valid-ies with minimal experimental mortality. Fifteene selected after having completed all quality con-ble 1).4,7,9,1013,29,33,37,4345,48,49dy was read and coded independently by 2 inves-ng different moderator variables. Because of theer of variables that may affect training effective-endent variables were grouped into the followingsubject characteristics: variables included agedy mass (kg), height (cm), previous experience,, level of fitness, sports level and type of sport) program exercises: variables included combina-ther types of exercise, intensity of session, type ofexercises and resistance; (3) program elements:

ncluded frequency of weekly sessions, programrop height, number of jumps per session, num-cises per session and rest intervals between seriess; and (4) outcome measurements: the type of

E.Sez-SezdeVillarreal

etal./Jo

urn

alofScience

and

Medicine

inSport13(2010)513522

515

Table 1Summary of characteristics of all studies meeting the inclusion criteria.

Authors Gr Year Treatm n G Age W H Exp KPly Fit MFG ES Freq D wk Int BH NoJ NoE Tply R JL Test

Blakey et al.9 E 1987 Ply + WT 31 M 19.5 NR Y N 11.43 0.37 3 8 Mod 40 30 1 DJ NR 1RM PRESSBuckley et al.10 E 2003 Ply + WT 26 M 23.5 NR N N 65 1.3 3 8 Low 3 C N 1 RM PRESSClutch et al.11 E 1983 Ply + WT 12 M 20.9 77.7 179 NA N N 18.56 1.5 2 4 Low . 40 1 SJ 120 N 1RM SQUATClutch et al.11 E 1983 Ply + WT 12 M 20.9 77.7 179 NA N N 10.59 0.79 2 4 Low 30 40 1 DJ 120 N 1 RM SQUATClutch et al.11 E 1983 Ply + WT 12 M 20.9 77.7 179 NA N N 14.58 1.22 2 4 Low 75 40 1 DJ 120 N 1RM SQUATFatouros et al.12 E 2000 Plyo 41 M 21.1 83.4 178 NA N B 16.4 1.3 3 12 H 30 150 5 C N 1 RM SQUATFatouros et al.12 E 2000 Ply + WT 41 M 20.1 79.9 178 NA N B 36.1 2.05 3 12 H 30 150 5 C Y 1RM SQUATFatouros et al.12 C 2000 41 M 20.5 80.8 181 NA B 1.7 0.07 1RM SQUATFowler et al.29 E 1995 Ply + WT 18 M 22.7 77.5 181.5 Reg Y G 17 0.97 4 3 H 50 2 SJ Y 1 RM SQUATFry et al.48 E 1991 Ply + WT 14 F 19.6 64.3 171.9 Nat N E 14.1 1.11 2 12 Mod . 7 C N 1RM SQUATHerrero et al.44 E 2006 Plyo 40 M 20.8 79.7 179 NA N N 3.99 0.13 2 4 H 100 . C 180 N ISOMETRICHerrero et al.44 E 2006 Ply + EMS 40 M 21.4 80.2 179 NA N N 40.1 1.69 4 4 H 100 . C 180 N ISOMETRICKramer et al.37 E 1983 Ply + WT 28 F 21.3 66.5 170 Nat Y E 48 0.81 3 9 Mod 30 60 4 S + D N 1RM SQUATLyttle et al.33 E 1996 Plyo 39 M 23.9 79.1 182.3 Reg N G 14 0.57 2 8 Mod 40 1 SJ N 1RM SQUATLyttle et al.33 E 1996 Ply + WT 39 M 23.8 72.5 178.4 Reg N G 15 0.72 2 8 Mod 20 10 1 DJ N 1RM SQUATLyttle et al.33 C 1996 39 M 20.6 74.2 177.3 Reg G 2.6 0.06 1RM SQUATMaffiuletti et al.7 E 2002 Ply + EMS 20 M 21.8 80.5 190.7 Reg Y E 20.3 1.11 3 4 Mod 40 50 2 C + D 180 N ISOKINETICMaffiuletti et al.7 C 2002 20 M 22.3 75.2 180.6 Reg E 5.6 0.17 ISOKINETICMartel et al.45 E 2005 Ply + Sw 19 F 15 64 167 Nat N G 9.5 0.41 2 6 Mod C 30 N ISOKINETICMartel et al.45 C 2005 19 F 14 57 164 Nat G 5 0.11 ISOKINETICPolhemus et al.49 E 1980 Ply + WT 29 M 25 NR Y G 20.08 0.66 3 6 H 45 50 3 DJ 60 N 1RM SQUATPolhemus et al.49 E 1980 Ply + WT 32 M 25 NR Y G 29.37 1.38 3 6 H 45 50 3 DJ 60 Y 1RM SQUATSez-Sez de

Villarreal et al.13E 2008 Plyo 42 M 22.3 75.6 174.7 NA N N 21.5 0.67 1 7 H 60 60 1 DJ 60 N 1 RM PRESS

Sez-Sez deVillarreal et al.13

E 2008 Plyo 42 M 23.1 80.1 176.6 NA N N 29.59 0.75 2 7 H 60 60 1 DJ 60 N 1RM PRESS

Sez-Sez deVillarreal et al.13

E 2008 Plyo 42 M 21.8 72.68 175.5 NA N N 50.56 1.62 4 7 H 60 60 1 DJ 60 N 1RM PRESS

Sez-Saz deVillarreal et al.13

C 2008 42 M 23.6 78.56 180.3 NA N 16 0.28 1RM PRESS

Wilson et al.4 E 1993 Plyo 13 M 22.1 71.6 174 NR Y N 1.3 0.02 2 10 Mod 20 60 2 DJ 180 N ISOMETRICWilson et al.4 C 1993 13 M 24.1 76.1 173 NR N 6.22 0.03 ISOMETRICWitzke et al.43 E 2000 Plyo 25 F 14.6 61.2 164.3 Reg N N 12 0.55 3 36 Mod 120 6 C N ISOKINETICWitzke et al.43 C 2000 28 F 14.5 61 165.1 Reg N 5.1 0.15 ISOKINETIC

Treatm (treatment), Plyo (plyometric), Ply + WT (weight-training), Ply + EMS (electrostimulation), Ply + Sw (in water)/JL (jump loaded): Y (yes), N (no), NR (not reported). Gr (group): E (experimental)/G(gender): M (male), F (female)/W (weight (kg)/H (height (cm)/Kply (knows plyometric) N (no), Y (yes)/test: Performance test. Exp (experience): Nat (national), Reg (regional), NA (no athlete) NR (notreported)/Fit (fitness): E (elite), G (good), N (normal), B (bad). Tply (type of plyometric): C (combined), S + D (SJ + DJ), C + D (CMJ + DJ), DJ, SJ/R (rest) (sec)/MFG (kg) (maximal force gains). Freq (frequencyDays/wk)/D wk (duration weeks)/Int (intensity): H (high), Mod (moderate) Low/BH (box height (cm))/NoJ (number of jumps)/NoE (number of exercises).

516 E. Sez-Sez de Villarreal et al. / Journal of Science and Medicine in Sport 13 (2010) 513522

strength teisometric ainvestigatothe same byof 0.90 is acoding proEach codinand was re

The EStion of the mexperimentHedges and

g = MpostSD

where Mpomean for tmeasureme

SDpooled =Fig. 1. Effect size (ES) of all studies meeting the inclusion criteria. Horizonta

st used to identify gains (1RM squat, isokinetic,nd 1RM leg press). The coding agreement betweenrs was determined by dividing the variables coded

the total number of variables. A mean agreementccepted as an appropriate level of reliability in thecedure.50 Mean agreement was 0.94 in our study.g difference was scrutinised by both investigatorssolved before the analysis.is a standardised value that permits the determina-

agnitude of the differences between the groups oral conditions.51 Gain ESs were calculated usingOlkins g,46 using formula (1):

M prepooled

(1)

st is the mean for the posttest and Mpre is thehe pretest, and SDpooled is the pooled SD of thents (2):

(Mpost Mpre)((n1 1) SD21 + (n2 1) SD22)/(n1 + n2 2)

It has bfor the macorrection

1 34m 9where m =

3. Statisti

To examables on tused.52,54,5ables (e.g.number oftest was usl bars represent 95% confidence intervals.

(2)

een suggested,5153 that ES should be correctedgnitude of sample size of each study. Therefore,was performed using formula (3):

(3)

n 1, as proposed by Hedges and Olkin.46

cal analysis

ine the effect of the categorical independent vari-he ES, an analysis of variance (ANOVA) was5 In the case of quantitative independent vari-age, height, duration of the treatment in weeks,repetitions per session) a Pearsons (r) correlationed to examine the relationships between ESs and

E. Sez-Sez de Villarreal et al. / Journal of Science and Medicine in Sport 13 (2010) 513522 517

Table 2Analysis for independent variables of subject characteristics.Independent variables Average (kg) SD F Level ES SD n rSubject chara

Age (y)Body massHeight (cmGroup size

Previous expe = 0.944FamiliarizeNot familia

Fitness = 0.304BadNormalGoodElite

Gender = 0.333MaleFemale

Sport level = 0.329NationalRegionalNo athletes

Sport activity = 0.687VolleyballBasketBody buildRowingSwimmingPhys. Ed. SAmerican f

* p < 0.05; E

variable vafor all analyproposed bresearch anrelative maconsidered(0.801.50

4. Results

The ana(0.97; n = 2compared t

With reindicate a(r = 0.451)was no signheight (r =of the ES (Tno significasured (i.e.,level and sp

There wsession andcteristics

(kg))

rience F(1,24) = 0.05 pd 25.27 18.91rized 23.72 16.34

F(3,24) = 1.27 p26.25 13.9324.24 18.5921.65 18.3428.52 14.88

F(1,24) = 1.18 p24.87 17.0520.91 18.16

F(2,19) = 1.19 p25.82 17.6014.07 4.1024.19 14.54

F(6,19) = 0.655 p14.63 5.417.19 2.56

ing 13.21 2.9948.23 7.3220.23 9.93

tud. 27.12 16.69

ootball 49.72 13.56S: effect size; SD: standard deviation; n: sample; level: alpha level; r: Pearsons co

lues.52 Statistical significance was set at p 0.05ses. The scale used for interpretation was the oney Rhea,56 which is specific to strength trainingd the training status of the subjects to evaluate thegnitude of an ES. The magnitudes of the ESs wereeither trivial (1.5) (Fig. 1).

lysis revealed that the average ES of the PT group4; 24.25 kg) was significantly higher (p < 0.05)o the ES of controls (0.11; n = 7; 4.25 kg).gards to the subject characteristics, the resultssignificant correlation coefficient for body masswith the magnitude of the ES. However, thereificant correlation coefficient for age (r = 0.242),

0.396) or group size (r = 0.05), with the magnitudeable 2). Results of the ANOVA comparisons werent effects (p > 0.05) in any of the variables mea-previous experience, fitness level, gender, sportort activity).as a significant effect regarding the intensity ofdifferent combinations of PT (p < 0.05). No dif-

ferences inexercises otance (Tabl

There wfrequencyno significa(wk) (r = repetitionsper sessionferences instrength tes

5. Discuss

The resvious studis an effecstrength peThus, the rPT couldin sportsmance. Thevidence fable inform24 0.24219 0.451*19 0.39624 0.05

0.90 0.58 81.39 0.95 16

1.67 0.53 20.89 0.55 120.98 0.41 70.81 0.35 3

1.01 0.62 200.72 0.30 4

0.63 0.58 30.64 0.31 61.17 0.58 10

0.87 0.40 20.41 10.80 0.49 60.80 10.50 10.97 0.59 6

0.80 0.51 2

rrelation coefficient: p: alpha level.

ESs were found among the type of plyometricr among programs with or without added resis-e 3).as a positive relationship (p < 0.05) between the

of sessions per week (r = 0.439) with PT ES, butnt effects were found between program duration0.218), drop height (cm) (r = 0.031), number ofper session (r = 0.223) and number of exercises(r = 0.152) with the PT ES (Table 4). No dif-ES (p > 0.05) were found among the different

ts (Table 5).

ion

ults of this investigation support numerous pre-ies4,9,11,13,33,43 that have concluded that PTtive training method for the improvement ofrformance (ES = 0.97; i.e., plyometric group).eported strength gains of >20 kg resulting frombe of practical relevance for trained athletes

aiming at achieving optimum strength perfor-e present meta-analysis offers robust quantitativeor this conclusion and provides some valu-ation concerning the importance of controlling

518 E. Sez-Sez de Villarreal et al. / Journal of Science and Medicine in Sport 13 (2010) 513522

Table 3Analysis of variance results on the differences of ES between various elements of plyometric training independent variables of program elements.

Independent variables Average (kg) SD F Level ES SD nProgram exercisesCombination with other types of exercise F(3,24) = 3.383 p = 0.035*

Plyometric 19.99 13.93 0.64 0.48 8Ply + weight-training 27.76 19.53 1.21 0.57 13Ply + electrostimulation 30.27 14.07 1.42 0.41 2Ply in water 9.56 0.41 0.41 1

Intensity of session F(2,24) = 8.98 p = 0.006*High 31.46 17.02 1.32 0.69 10Moderate 17.27 11.54 0.61 0.30 10Low 27.18 25.42 1.20 0.29 4

Types of plyometric exercises F(4,24) = 1.03 p = 0.425Combined 0.97 0.67 8Squat jumpDrop jumpSJ + DJCMJ + DJ

Resistance = 1.32Added weiWeightless

* p < 0.05; S etric; ESlevel.

Table 4Pearsons cortraining gains

Training prog

Frequency sesProgram duraDrop height (Number of juNumber of exRest between

* p < 0.05; n

some deteperformanc

Some aucal ability ajoint coordimprovemeinitial strenanalysis indmore expeness levelswith poor fi

subje

Table 5Analysis for i

Independent v

Outcome meaStrength te1RM SquaIsokineticIsometric1RM leg pr

* p < 0.05; E25.43 19.4816.52 2.3125.16 17.4127.59 18.8520.31 12.32

F(1,23)ght 37.49 21.21

23.39 16.54J: squat jump; CMJ: countermovement jump; DJ: drop jump; Ply: plyom

when

relation coefficients (r) between various program elements and.

ram variables n r p

sion/week 26 0.439 0.05*tion (wk) 26 0.218cm) 16 0.031mps per session 23 0.223ercise/session 23 0.152sets (s) 13 0.243: sample, r: Pearsons correlation coefficient: p: alpha level.

rminant variables for the improvement of thee.thors suggest that PT requires appropriate techni-s well as sufficient levels of muscle strength and

ination.57,58 However, Wilson et al.,59 report thatnt in performance from PT is not determined bygth level. Similarly, the results of the present meta-icate lower but not significantly different ESs for

rienced subjects and with good or excellent fit-in comparison with less experienced subjects andtness (Table 2). These results might indicate that

quate technlevel. Howecising regufirst weeksviduals meFurthermorsubjects dutraining istem, such amotor unitity, and incthe antagongist muscleAagaard etimprovemeexplained bone explanindividuals

An interstrated simHowever, t

ndependent variables of outcome measurement.

ariables Average (kg) SD F Lsurementst F(3,24) = 1.22 pt 24.90 18.6

18.37 10.0619.03 18.79

ess 33.88 14.99S: effect size; SD: Standard deviation; n: sample; level: alpha level.1.01 0.46 31.09 0.64 110.61 11.11 1

p = 0.2631.29 0.65 30.94 0.47 20

: effect size; SD: standard deviation; n: sample; level: alpha

cts can perform plyometric exercises with ade-ique, the training gains are independent of fitnessver, it is known that when less fit people start exer-larly, they could achieve higher gains during theof training in comparison with well-trained indi-

asured by most of the indices of physical fitness.60e, a major part of the improvements in untrainedring the initial weeks in ballistic-type strengthprobably due to adaptations of the neural sys-s increased motor unit firing frequency, improvedsynchronisation, increased motor unit excitabil-rease in efferent motor drive. Also, a reduction of

ist and an improved co-activation of the syner-s may explain part of the changes.61 In a study ofal.,62 the major component of the training inducednts after 14 weeks of resistance training, werey increases in efferent neural drive. This may beation for the higher changes in less experienced.esting finding of this study was that men demon-ilar gains compared with women (Table 2).

he large difference in sample size between men

evel ES SD n

= 0.325*1.11 0.57 150.57 0.38 30.67 0.58 31.01 0.52 3

E. Sez-Sez de Villarreal et al. / Journal of Science and Medicine in Sport 13 (2010) 513522 519

and women and the small number of ESs available mayaccount for this observation. The reasons for this similarityare not clear. Muscle strength (an absolute value) of womenis equivalenmuscle stregender diffwas superiity to usereported thfibers65 annervous symuscle streteristics (minfluential.muscle crobetween seper cross-sto previouselastic enerin women vthe abilitypared withinferior inwomen are

ticity energsmall, buton a gendethe central

In the picantly higtypes of eplyometricmight be attraining proexercises (ietc) used asibility thawere expothe other gbetween gries made awhen compence is thesubjects. Tfollowed thlower intenexercise temulti-jointcase, the oletic perforweight-traiwill be optat a traininput of theperform bedue to the f

facilitate the neural and mechanical mechanisms that enhanceperformance in activities of maximal force.

The results of this investigation suggest that when thesity isin streminedMJs

rent cht utiliombincomp

ever, ts, andf a sin

on stjumpsested tse iteuralfferenly conJ inv

ts of o, our

ts whes (i.e.That

e (i.e). ThisT en

. Perfoforceouslyct forlocom

stimue effeme re

hts (ve.12,29,ing wfar suometrno sige 3). Thts inance.ionalct timtive thional wlume

ken inanalysbetwe

ficialt to 5060% of men when we compare isometricngth among men and women.63,64 Furthermore,erence was found in SSC ability, and the abilityor in men as compared with women. The abil-SSC in women was 64.1% that of men. It wasat the dominance in women of type I muscled a difference in the degree of inhibition in thestem66 may be related to the gender difference inngth. In addition, muscular morphologic charac-uscle fascicle length and pennation angles) may beHowever, when strength is expressed relative toss-sectional area, no significant difference existsxes, which indicate that muscle quality (peak forceectional area) is not sex specific.64,67 Accordingstudies,68,69 it was reported that the ability to usegy following eccentric muscle action is superiors. men. Komi and Bosco23 have pointed out that

to endure extension load is superior in men com-women, but the ability to use elastic energy is

men. Furthermore, Aura and Komi68 report thatsuperior in storage and recycling ability of elas-y compared with men when the extension load isinferior when the load is large. This may dependr difference of muscle stiffness and inhibition ofnervous system.69resent study, strength improvements are signif-her when plyometrics are combined with otherxercises (i.e., plyometric + weight-training and+ electrostimulation) (Table 3). The differencestributed to several reasons. First, the nature of thetocol, the type of plyometric and weight-training

.e., full-squats, parallel squats, Olympic exercises,nd second, the training stimulus. There is a pos-t the subjects in the combination training groupsed to a higher training stimulus than those inroups, that is, the total workload was not equatedoups. It would be very interesting if future stud-n attempt to equate workloads between groupsaring different training methods. Another differ-model used to provide the training stimulus to

raining intensity, volume, and exercise selectione principle of progressive overload, starting withsities, single-joint exercises, and less complex

chniques, and progressing to higher intensities,exercises, and more complex techniques. In any

ptimal training strategy to enhance dynamic ath-mance appears to be a hybrid between traditionalning and PT. That is, strength performance gainsimised by the use of plyometric + weight-trainingg load that maximises the mechanical force out-exercise. Hence, the combined group tended totter in activities of maximal force. This may beact that this combination of exercises may better

intenmentdeterby Cdiffeferenthe cgainsHowCMJuse o

of PTticalsuggbecauand nto dimaina CMresulicallyeffecjumpused.manc

pressthat Pforceimalpreviimpaorous

forcecan b

Soweiggainsjumpwere

to plycated(Tablweigformadditcontaeffecaddit

Vobe taOur(i.e.,benehigh during the session, there is a greater improve-ngth performance (Table 3). Some authors40,7072that performance is higher during DJs, followed

and then SJs. This is mainly attributed to thearacteristics of movement and, thus, to the dif-

sation of SSC characteristics. For these reasons,ation of various exercises may result in higherared with the performance of each exercise alone.he present results show that a combination of SJs,DJs demonstrates similar ES compared with thegle type of exercise (Table 3). The specific effectsrength performance in the different types of ver-could be of particular importance. It has been

hat PT is more effective in improving performanceenhances the ability of subjects to use the elasticbenefits of the SSC.39 This could also be attributedces in the use of SSC characteristics.23,40 A SJsists of a concentric (push-off) phase, whereasolves an eccentric and concentric phase.18 Theur study do not support these suggestions. Specif-data indicate that PT produces similar positivether fast SSC jumps (i.e., DJ) or concentric-only, SJ), or even slow SSC jumps (i.e., CMJ), areis, all the treatments increased strength perfor-

., 1RM squat, isometric, isokinetic or 1RM legagrees with previous results11,37 that have shown

hances an individuals ability to rapidly developrming PT involves the rapid development of max-

during the eccentric phase of motion. It has beenreported that the body experiences tremendous

ces during foot contact with the ground in vig-otion,7377 thus, one may speculate that muscle

lus during any PT (i.e., DJs, CMJs, and combined)ctive for strength development.search studies have shown that PT with additionalsts, barbell on the back, etc.) demonstrated higher

49 In addition, Wilson et al.,4 clearly showed thatith a barbell and traditional resistance trainingperior for increasing maximal strength comparedics. However, the results of the meta-analysis indi-nificant differences among the training conditionshis suggests in some cases, that using additional

training could not cause significant gains in per-It could be suggested, then, that training withloads might increase not only resistance, but alsoe. However, the longer the contact time, the lesse SSC.27 Therefore, superior training effects using

eights can not be guaranteed.and frequency are very important parameters toto account for an optimum PT program design.is suggests that training for less than 10 weeksen 6 and 10) with 3 sessions per week is more

than similar programs of longer duration. Simi-

520 E. Sez-Sez de Villarreal et al. / Journal of Science and Medicine in Sport 13 (2010) 513522

larly, treatment with more than 15 sessions increases strengthperformance, whereas performance of more than 40 repeti-tions per session seemed to be the most beneficial volume(Table 4).a short-terquency anweek), promance butof the impr(4 d wk1,the whole,ing the nummen doesing strengtcomparedalso suggesold over wadvantageo

6. Conclu

In concsignificantlimprovemeered as prain strengthimportanceperformancperform pltraining gahand, subjeefit equallyresults than10 weeks (ties (withthat will mimprovemeis a threshoincreases inimportantbine plyomsingle mod

Practical i

The effeof variabcharactesport acttrainingtaken infessionaapproachtechniqu

requirements, and potential injury analysis for a givensport.

For an individual athlete, initial training status and trainingperienions sach mnds idlevel

rence

raemerA, et al.ccupatiez-Seetermin

al jump009;23:ilson G

ffects o996;21:ilson G

ng loadports Eewtoneeks of

ttenuatetrengthalatest

romyostStrengtaffiule

lectro sed Sciardinalle durinond Relakey Jlyometres 1987uckleyn anaer

actor I.lutch Dnd weigport 19atourosostopo

raining,eg strenez-Seoderate

printing008;22:nderst

ive resi994;26:smusseuscle iauer T

or powe990;4:1However, in agreement with previous studies13m PT program with a moderate training fre-d volume of jumps (2 d wk1, 840 jumps perduced similar enhancements in strength perfor-greater training efficiency (number of jumps/%ovement) compared with high training frequency1680 jumps per week). Conceptually taken onthe present data would indicate that increas-ber of jumps in previously moderately trained

not seem to be the best stimulus for improv-h performance during short-term training periodswith high jump-training volumes. These resultst that there is a maximum training volume thresh-hich further increases in volume are no longerus.

sion

lusion, the present study demonstrates that PTy improves strength performance. The estimatednts in strength as a result of PT could be consid-ctically relevantfor example, an improvement

of >20 kg (i.e., ES = 0.97) could be of highfor trained athletes in sports relying on strengthe. According to our results, when subjects can

yometric exercises with adequate technique, theins are independent of fitness level. On the othercts of both high and lower physical condition ben-from PT, although men obtain similar strengthwomen after PT. A training volume of less than

with more than 15 sessions) using high intensi-more than 40 jumps per session) is the strategyaximise the probability of obtaining significantnts in performance. It is also probable that thereld training volume threshold over which furthervolume may no longer be advantageous. Another

conclusion is that it is more beneficial to com-etrics with weight-training than to utilise only theality.

mplications

cts of PT may vary because of a large numberles, such us training programme design, subject

ristics (gender, age), training level, the specificivity, familiarity with PT, program duration, andvolume or intensity. These variables should beto account by strength and conditioning pro-ls, who must consider the most appropriate PT

based on the fundamental movement patterns,e, volume, frequency, intensity, energy system

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Does plyometric training improve strength performance? A meta-analysisIntroductionMethodsStatistical analysisResultsDiscussionConclusionPractical implicationsReferences