a brief review, factors afeecting the length

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Journal of Strength and Conditioning Research, 2006, 20(4), 978-984 2006 National Strength & Conditioning Association Brief ReviewA B R I E F R E V I E W : F A C T O R S A F E E C T I N G T H E L E N G T HOE THE R E S T I N T E R V A L B E T W E E N R E S I S T A N C EE X E R C I S E S E T SJ E F F R E Y M W I L L AR D S O NPhysical Education Departm ent, E astern Illinois Univers ity, Charleston , Illinois 61920

ABSTRACT Willardson, J.M , A brief review: Factor s affectingthe length of the rest interval between resistance exercise sets.J. Strength Cond Res. 20 4):978-984.,2006.Research ha s in-dicated tha t m ultiple sets are superior to single sets for m aximalstrength development. However, whether maximal strengthgains are achieved may depend on the ability to sustain a con-siste nt numb er of repe titions over consecutive s ets. A key factorthat determines the ability to sustain repetitions is tbe lengthof rest interval between sets. Tbe lengtb of tbe rest interval iscommonly prescribed based on the training goal, but may varybased on several otber factors. The purpose of this review wasto discuss tbese factors in the context of different training goals.Wben training for muscular strength, the magnitude of the loadlifted is a key determinant of the rest interval prescribed be-tween sets. For loads less than 909c of 1 repetition maximum,3-5 minutes rest between sets allows for greater strength in-creases tbrough the m aintenance of training intensity. However,wben testing for maximal strengtb, 1-2 minutes rest betweensets migbt be sufficient between repeated attempts. Wben train-ing for muscular power, a minimum of minutes rest should beprescribed between s ets of repea ted m aximal effort movem ents(e.g., plyometric jumps). Wben training for muscular hypertrc-pby, consecutive sets should be performed prior to when full re-covery bas taken place. Shorter rest intervals of 30-60 secondsbetween sets bave been asfiociated witb higber acute increasesin growtb hormone, wbich may contribute to the hypertropbicefTect, Wben training for muscular endurance, an ideal strategymigbt be to perform resistance exercises in a circuit, witb short-er rest intervals (e.g., 30 seconds) between exercises that involvedissimilar muscle groups, and longer rest intervals (e.g., 3 min-utes) between exercises tbat involve similar muscle groups. Insummary, the length of the rest interval between sets is only 1component of a resistance exercise program d irected toward dif-ferent training goals. Prescribing tbe appropriate rest intervaldoes not ensure a desired outcome if otber components such asintensity and volume are not prescribed appropriately.KEY WORDS,recovery, fatigue, streng tb, power, hypertrophy, en-duranceI N TR O D UC TI O N

esistance trai nin g has been recognized as anessential component of a comprehensive fit-ness program for individuals with diverse fit-\^ ness goals. Individua ls may participa te in re-sistance training for rehabilitative reasons orin prep aratio n for stren uou s jobs such as firefighting, lawenforcement, or military service. Manipulation of trainingvariables is depend ent on the specific train ing goals of theindividual and the physical demands encountered duringdaily life (2, 4).A recent m eta-analysis by Rhea et al. (20) demonstrat-ed that when the training goal is maximal strength de-velopment, multiple sets per muscle group were superior

to single sets. However, the superiority of performimultiple sets per muscle group may depend on the abilto sustain consistent repetitions over consecutive s(22).The ability to sustain consistent repetitions is laly dependent on the length of the rest interval betwesets (12, 15,21 ,29, 30, 32-34). The length of rest intemust be sufficient to recover energy sources (e.g., adensine triphosphate [ATP] and phosphocreatine [PCrclear fatigue producing substan ces (e.g., H* ions), and store force production (2, 4, 10, 23, 31).Generally, the length of the rest interval between sis prescribed based on the training goal. The recommened rest interval increases when programs are designed strength or power (e.g., 2-5 minutes) and decreases whprograms are designed for hypertrophy (e.g., 30-90 sonds) or muscular endurance (e.g., less than or equal30 seconds) (2, 4). Although these recommendations pvide an important foundation for generalized exercprescription, the length of the rest interval may vabased on several factors (see Figure 1). Therefore, tpurpose of this review will be to discuss these factors arest interval length in the context of different traingoals.M U S C U L A R S T R E N G T HMuscular strength-oriented programs place primary ephasis on the maintenance of training intensity throulonger rest intervals of 2-5 minutes between sets (2, Longer rest intervals make greater strength increaspossible through greater consistency in the repetitioperformed for each set (12, 21 , 29, 32-34). Two studie sdate have compared strength increases resulting from dferent rest intervals between sets.Pincivero et al. (18) compared isokinetic strength creases in 2 groups assigned to either a 40-second or160-second rest interval between sets. Subjects in eagroup performed 4 sets of 10 maximal isokinetic k nee tensions and knee flexions at 90 degrees per secondtimes per week for 4 weeks, using a randomly assignleg. At the conclusion of the study, the 160-second group demonstrated greater peak torque in the quadceps and ham strings. The au thors concluded that the 16second rest interval led to greater strength increases bcause of a higher volume of work.Robinson et al. (22) compared squat strength increes in 3 groups assigned to either a 3-minute, 90-seconor 30-second rest interval between sets. Subjects in eagroup performed 5 sets of 10 repetitio ns 2 times per wefor 5 weeks. At the conclusion of the study, subjectsthe 3-minute group demonstrated greater strength creases vs. the other 2 groups. The autbors conclud

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REST INTERVAL 979

FIGURE 1 Factors affecting the length of the rest intervalbetween sets.th at the 3-minute res t in terval led to greate r s t re ngthincreases because of the abi l i ty to ma inta in a h ighe rt ra in ing in tens i ty .These s tudies demons tra ted that greater muscular re-covery via longer rest intervals between sets is the key togrea ter s t re ngth increases (18 , 22) . However , researchhas dem ons tra ted tha t the length of the res t in terval nec-essary to facili tate sufficient recovery can vary based onseveral factors (see Figure 1). Two of the most frequentlystudie d of the se factors are t he type of muscle action andthe magnitude of the load lif ted; these will be discussedbelow.

Type of Muscle Act ionStul l and Clarke (27) compared pat terns of s t rength re-covery for the wrist flexors following isotonic and isomet-ric fatigue tasks conducted on separate days. Isotonic fa-tigue was induced as subjects performed repeated maxi-mal contractions for 3 minutes. Isometric fatigue was in-duced as subjects sus ta ined a maximal isometr ic muscleact ion unt i l s t reng th had deter iorated to the f inalstre ng th level of tbe isotonic testin g condition. Each sub-ject then performed a maximal contraction at differenttime intervals following the fatigue task (see Table 1).The key finding was that for both the isotonic and iso-metr ic condi t ions , s t rength levels had re turned to ap-proximately 98^^ of initial values in less than 4 minutes.However, isotonic s trength initially recovered more rap-id ly than isometr ic s t rength . The authors a t t r ibuted th isto s lower reestablishment of intramuscular blood flow fol-lowing the isometric condition.

Bilcheck et al . (5) examined the time necessary forstre ng th recovery of the q uad ricep s following an isoki-netic fatigue task. Subjects attended 4 testing sessionsduring which 3 sets of3 maximal contractions at 120-S 'were performed with 1 minute res t in tervals betweense ts . Subjects were te sted for s treng th a t 2.5, 5, and 10min utes in to the recovery per iod . The resul ts dem ons tra t -ed no significant differences between the torque producedprior to the fatigue task and the torque produced at eachtest point during the recovery period. The authors con-cluded that isokinetic resis tance exercise protocols couldutilize 2.5 minutes between sets without fear of compro-mising force production.

These s tudies sugges t that regardless of the type ofmuscle act ion , approximately 75% of mu scular s t reng this recovered within the firs t minute, with an additional2-3 m inu tes need ed to recover full s t ren gth (5 , 27).Therefore, when performing workouts designed for mus-

TABLE 1. Sum mary recovery of mu scular s trength vs. muscular endurance.='Authors Muscles Task Measure Time Recovery

Bilcheck et al. (5)Sahlin and Ren (23)

Stull and Clarke (27)

Yates et al. (36)

Knee extensors 3 sets of 30 maxim al isokinetic con- Stre ngthtractions at 120 ; s 'Knee extensors Sustained isometric muscle action at Strength66%ofMVC until force declined to50%ofMVCForearm flexors 30 isotonic maximal contractions per

minute for 3 minutesSustained maximal isometric muscle Strengthaction

Elbow flexors 38 isotonic repetitions per minute atone-sixth MVC

2 min 30 s2 min

10 010 0

EnduranceStrength

Strength

Endurance

4010351110351123302720

m inssm inm inssm inm inm inm insm inm inm in

1055

10555555

ss

ssss

10 05684969836496880899735507590

* In the studies that asst'ssed recovery of muscular strength, a single maximal voluntary contraction (MVCi was performed atdifferent time intervals following the fatigue task. In the studies that assessed recovery of muscular endurance, the fatigue taskwas repeated at different recovery intervals and the fatigue time was compared with the fatigue time of the Initial task.


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980 WiLLARDSONTABLE2. Rest interval length and bench press performance.'

Author Load Sets Rest RepsKraem er (12) lORMRichmondandGodard (21) 75 lRM

Toddet al. (29) 60 IRM

90 'ofIRM

3352345234525522323

2538222356723444722262633959758882327

WillardsonandBurkett (32) 8RM

WillardsonandBurk ett (33) 15RM

WillardsonandBu rkett (34) 50 ofIRM8 ofIRM

*In allstudies,theloadwasheld constantand all sets wereperformed to the point of muscular failure. Rest measuredinminutes; Reps = total repetitions; IRM = 1 repetition maxi-mum.cular strength, resting3 or 4minutes might be beneficialto allowfor full recovery priorto thenext set.Ofcourse,the amountofmuscle ma ss involved an d th e type ofmus-cle action must alsobeconsidered. Forexample, move-ments suchas thedeadliftandsquat, which involve bothisotonic (e.g., hip ex tensors, kn ee extenso rs) and isometric(e.g., wrist fiexors, abdominals) muscle actions, might re-quire 34minutes rest between sets. However, w hentraining small muscle groups (e.g., wrist flexors)orlargemuscle groups (e.g., quadriceps) in isolation, 1-minuterest intervals might be sufficient.Magnitudeofthe oad iftedRelatively few studies have been conducted that exam-ined the effectofrest interval length onthesustainabilityof repetitions during traditional isoinertial resistance ex-ereises.Thestudies tha t currently exist have almostex-clusively exam inedthebench press exercise (see Table 2).The maintenance of repetitions duringthe bench presshas been shown behighly dependent on themagnitudeof the load lifted.Kraemer (12), RichmondandGodard (21), Toddet al.(29),andW illardson and Burkett (32-34) demonstratedthat when training with submaximal loads between 50and 90 of repetition maximum (IRM), longer restin-tervalsof 3-5 minutes between sets allowedformoreto-tal repetitionsto becompleted duringaworkout.Incon-trast, Weiret al. (30) and Matuszak et al. (15)demon-strated that when assessing maximal bench pressandsquat strength, longer rest intervals werenot asimpor-

tant. These authors reported that a maximal squatabench press were repeatable witha1-minuterest interbetween repeated attempts.Basedon theresultsofthe aforementioned studie srecovery threshold appears to exist when training wloads greater thanorequalto90 ofIRMatwhich reing1-2 minutes between setsissufficient (15, 30). Cversely, when train ing with loads less than 90 'ofIRresting3-5minutes between setsisnecessarytosustrepetitions without large reductionsinthe training intsity (12, 21 , 29, 32-3 4). Simply state d, recovery followinmaximalornear-m axima l lifts app ears to occur more ridly relative to recovery following submaximal liftspformedtofailure. T his ob servationisconsistent with pvious studies, which demonstrated shorter recovery timof muscular strength vs. muscular endurance(seeTa1) (5, 23, 27, 36). Sahlinand Ren(23) concluded.

Thus there is an apparent paradoxin that acidosis doesnotpair contractile force but appears to limit endurance durinsustained contraction. Theexplanation ofthis paradox couldtha t the link between H' accumulation and muscle fatigueindirect. One possibility is that acidosis through H -mediainhibition ofphosphofructokinase resu lts in a reduced capato generate ATP through glycolysis. Duringa sustained conttion PCr decreases to lowlevels and ATPgener ation fromcolysis will become essential for theabilityto maintain a hrateofADP rephosphorylation, andacidotic inhibition ofglyysis could then impairthe contractility. However, during recery whena partial resynthesisofPC rhasoccurredit is unliktha talimitation of glycotysiscanimpairthecapacity to geneAT P(andthu s maxim al force), becausethebreakdown of PCthe most rapid process inADP rephosphorylation (p.653).

MUSCUL R POWERBecause training exercises designedtoincrease m uscupower require maximal rates of force development, longrest intei-valsof2-5 minutes b etween sets have been rommendedtoallowforgTeater neurological recoveryconsistencyinmovement mechanics (2, 4). However, liresearch exists regarding how much rest is neededtween sets of single maximal-effort movem ents (e.g.,Ipower clean) vs. repeated -max imal effort-moveme(e.g., plyometric jumps). Longer rest intervals of 2-5 miutes mightbe necessary between setsofrepeated mamal effort movements, becauseof the primary involme nt of the glycolytic energy system and theneed to cfatigue-producing substances (e.g., H* ions) frommuscles (23,31).In contrast, shorter rest intervals of 1-2 minumightbe sufficient between setsofsingle max imal-efmovements, becauseof the primary involvement ofphosphagen energy system (15, 23,30,31). AccordingFleck andKraemer (7), 90 ofphosphagens can becovered within 1minute foUoviangahigh-intensity retance exerciseset. In thecontextofmuscu lar power,ofthe rest interval researchtodateisapplicabletosof repeated maximal-effort movements.Pinciveroet al. (19) compared quadriceps and hstring peak torque, total work,and average powergroups assigned to eithera40-secondor a160-second interval between sets. Both groups performed4setsoreciprocal, concentric, maximal isokinetic knee extensiand fiexion repetitions at 90s' . Results demonstrathat from set 1 to set 4, the 40-second rest group


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RESTINTERVAL 981significant reductions in peak torque (quadriceps16%,hamstrings 12%), total work (quadriceps19%,hamstrings19%), andaverage power (quadriceps 19%, hamstrings18%). Conversely,the160-second rest grouphad no sig-nificant reductionsinpeak torque (quadriceps 2.2%, ham-strings 2.4%), total work (quadriceps 2.8%, hamstrings5.7%),andaverage power (quadriceps 2.4%, hamstrings5.7%).

In a follow-up study, Pinciveroet al. (17)usedthesame experimental design, withtheexception that4setsof 20 maximal isokinetic knee extensions were performedat 180''s '. Results demonstrated that from set 1 to set4,the40-second rest grouphadsignificant reductionsinpeak torque (29%), total work (47%), and peak power(46%).Conversely, the 160-second rest group hadmuchless reductioninpeak torque (11%), total work (25%), andaverage power(24% ).Theauthors concluded that longerrest intervals allowed formaximal torque andpowertobe sustained, wbich mayresult in greater increasesinstrength andpower when appliedin along-term trainingprogram.Abdessemed et al. (1)demonstrated comparablere-

stilts when recovery duration was examinedonmuscularpowerandblood lactate during the bench press exercise.Subjects performed 10 sets of 6 maximal effort repetitionsat 70% of their IRM,andwitha 1-,3-,or5-minute restinterval betweens sets. Theresults demonstrated thatfrom set 1 to set 10, themean powerdid notdecreasesignificantly for the 3- or5-minute rest conditions(4.8%and 2%, respectively),but diddecrease significantlyforthe 1-minute rest condition (27%). Decreases in meanpower with the1-minute rest condition were negativelyand highly correlated toincreases inblood lactate (indi-vidual correlations ranged from 0.64 to 0.99). The authorsconcluded that resting1minute between sets was notsuf-ficient forlactate tobuffer thefatigue producing effectsof H ions.Overall, the aforementioned studies indicate thatwhen performing sets ofrepeated maximal effort move-ments,3minutesofrestissufficient between consecutivesets 1 ,17, 19). A limitation of the aforementioned studieswas the assessment of only isokinetic movements and thefree weight bench press, which mayhave limited appli-cationto themovements encountered during sports com-petition. Therefore, future research shouldbeconductedto determine how different rest intervals affect the main-tenanceofpower during standing upper-andlower-bodyexplosive resistance exercises. Forresistance exercisesthat involve single maximal effort movements (e.g., IRMpower clean), future research should examine whether1-2 minutesissufficient tomaintain powerandmovementmechanics between repeated attempts.MUSCUL R HYPERTROPHYIn strength-type regim(3ns,the recommended rest inter-valof2-5 minutes between setshasbeen showntoallowfor consistent repetitions, without loweringthetrainingintensity (12, 21, 22, 29, 32, 34). Conversely,inhypertro-phy-type regimens,therecommended rest interval of 30-90 secondsis notsufficient tosustain thetraining inten-sity over consecutive sets(8, 13, 14,16). Therefore,per-forming tbe nextsetprior to when full recovery has takenplaceis considered more important. However, consistenttraining with short rest intervals mayresult inadapta-tions that allowfortraining intensityto besustained.

Kraemeret al.(14) found that specific training prac-ticescanreducetheamountofrest needed between sets.In this study,9male bodybuildersand 8male power lift-ers performed a 10-station circuit that included resis-tance exercises for the entire body. Each exercise was per-formed with load and rest intervals conducive to thetraining practices of competitive bodybuilders. Three con-secutive sets for each exercise were performed with alORM load that was progressively loweredtoallowfor 10repetitions in each set.Subjects rested 10secondsbe-tween sets,and30-60 seconds between exercises.

Thekeyfindingwas that thebodybuilders were ableto sustainasignificantly higher mean percentageofIRMduring performance of the bench press and leg press sets.Kraemeretal. (14) concluded that the bodybuilders wereabletoresist the effects of fatigue because of adaptationsassociated with thebodybuilding style of training (e.g.,high volume with short rest intervals). These adaptationsmight include increases incapillary and mitochondrialdensityand in theability to buffer and transportH'ionsoutofthe muscles.Few studies have compared differences inhypertro-

phy consequent to workout protocols that involve rela-tively short vs. long rest intervals between sets. The gen-eral recommendation forshort rest intervals was derivedfrom research that examined acute anabolic hormonal se-cretions. Kraemeret al.(13) demonstrated that ahyper-trophy-type regimen, consisting of 3sets of 8 exercisesperformed withalORM loadand1-minuterest intervalsbetween sets, produced greater acute increasesingrowthhormone (GH) vs.astrength-type regimen, consistingof5 setsof5 exercises performed witha5RM loadand a 3-minute rest intervals between sets. McCalletal. (16) useda similar hypertrophy-type regimenin a12-week trainingstudy that demonstrated significant correlations betweenacute GH increasesand therelative degree of typeI (r ^0.74)andtype II r =0.71) muscle fiber hypertrophyinthe biceps brachii.

Although these studies provided probable evidencethat moderate-intensity resistance exercises combinedwith short rest intervals are superior for hypertrophytraining, there were limitations. Forexample, Kraemeretal. (13) did notconduct atraining program,and con-sequently hypertrophy was notassessed. Kraemer et al.concluded, Thelink between the concomitant in vivochanges of endogenous anabolic hormones and tissuegrowth has not been specifically determined, and in-creased concentrations ofcirculating anabolic hormonesmay notreflect anabolismat thetissue level (p.1447).Although McCallet al. (16) didconduct atrainingpro-gram and hypertrophy was assessed, only 1 type of work-out regimenwasexamined.

Gotoet al. (8)addressed these limitations by compar-ing differences in acute growth hormone secretionandquadriceps muscle cross-sectional area consequent to a10-week periodized resistance program for the lowerbody. Subjects were assigned toeither a hypertrophy/combination (HC) group in = 8) or a hypertrophy/strength (HS) groupin =9).Duringthefirst6weeksofthe study,the HC and HSgroups performed ahypertro-phy-type regimen 2daysperweek, which consisted of 3sets eachofleg extension and legpress with30secondsrest between setsand 3-5minutes rest between exercis-es.For each exercise, the resistance was progressively ad-justed toallowfor10-15 repetitionsoneachset.


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982 WILLARDSONDuring weeks7through 10,theHS groups performeda strength-type regimen2days per week, which consistedof 5 sets eachofleg extensionand legpress with3 min-utes rest between setsand 3-5minutes rest betweenex-ercises. For each exercise,theresistance was progressive-ly adjusted toallowfor 3-5repetitions ineach set. TheHC group performed acombination-type regimen, whichwasthesameas thestrength-type regimen, withthe ex-

ception that anadditionalset wasperformed 30secondsfollowing thefifthset ofeach exercise with a resistancethat allowedfor25-35 repetitions.Gotoet al. (8) demonstrated that acute increasesingrowth hormone were highest after thehypertrophy-typeregimen, followedby thecombination-type regimen,andthen thestrength-type regimen. Duringthehypertrophyphase (first 6weeks),the HS and HCgroups increasedquadriceps cross-sectional area equally. However, duringthe subsequent strength phase (weeks 7 through 10), onlytheHCgroup continued to increase cross-sectional area.The authors concluded that moderate-intensity loadscombined with short rest intervals (e.g., 10-15RM with30 seconds to 1minute rest between sets) were superior

to high-intensity loads with long rest intervals (3-5RMwith3minutes rest between sets)forhypertrophy.Further, after transition to a strength-type regimen,a light "burnout"setperformed 30seconds followingthelast heavy set waseffective for continued hypertrophy.However,as thename implies,thehypertrophy-type reg-imenwasmost effective; thismayhave been inpartbe-causeof repeated exposure togreater acute growthhor-mone secretions. Overall, short rest intervals betweensetsareonly 1componentof aprogram designedfor hy-pertrophy andappearto bemost effective when utilizedin conjunction with moderate intensity sets performedtomuscular failure.

MUSCUL R ENDUR NCEVery little research hasbeen conductedon theeffectofdifferent rest intervals between setsonmuscular endur-ance adaptations. Because muscular endurance is definedastheabilitytosustain submaximal contractions over ex-tended periods of time,thecurrent recommendationis forrest intervalsofless thanorequalto 30seconds betweensets (2, 4). Studies that validatedthestrength/endurEuicecontinuum demonstrated that resistance programs in-volving low resistanceandhigh repetitions were superiorto programs involving high resistance and low repetitionsfor increasing muscular endurance 3,6,26). However,nostudies have examined changes in muscular endurancewhen low-resistance and high-repetition programs arecompared with different rest intervals between sets.Willardson and Burkett (33)compared the sustain-ability of squatandbench press repetitions with differentrest intervals between sets. Five consecutive sets wereperfonned with a15RM loadand a30-second,1-minute,or 2-minute rest intei-val between sets. Tbe load was keptconstant overall5 setsand thepercentage declineinrep-etitions wascompared between rest conditions. The re-sults demonstrated thatforall rest conditions, significantdeclinesinrepetitions occurred betweenthefirstset andthe fifth set for both exercises. However, the 2-minuterest condition afforded greater sustainability of repeti-tions, with more total repetitions completedvs. the 30-second and1-minute rest conditions (seeTable 2). Theauthors concluded that muscular endtirance training pro-

grams that involve30 seconds rest between sets shoulower the training intensity over consecutive setsinordto sustain repetitions within therange conducivetottraining goal.The optima programformuscular endurance trainilikely includesacombinationoflow resistance, highreetitions,andshort rest intei-vals between sets (2, 4). Fthis reason, a circuit strategy hasbeen hypothesizedbe idealformuscular endurance training 35).Using tstrategy, shorter rest intervals (e.g.,30seconds)are pscribed between resistance exercises that involve dissiilar muscle groups, while longer rest intervals (e.g.,minutes)areprescribed between resistance exercises thinvolve similar muscle groups. Because setsfor thesamuscle groupare notperformed consecutively, highreetitionscan besustained.P RACT I CAL AP P L I CAT I ONSIn summary,thelengthofthe rest interval between sis only 1componentof a resistance exercise programrected toward different training goals. Prescribing the apropriate rest interval doesnotensureadesired outcoif other components suchasintensityandvolumeare prescribed appropriately. Although recommendationseist regarding the appropriate rest interval basedon ttraining goal, several factors mayshorten or lengththese generalizations (seeFigure 1). Therefore, strengcoaches should consider individual differences and ttype ofworkout being performed when prescribingtrest interval between sets.

When training for muscular strength, longer resttervals are generally prescribed toallow forgreatercovery andmaintenance of training intensity. Howevthe length of the rest intervalcanvary, depending ontmagnitudeof the load lifted. For submaximal lifts, lthan 90%ofIRM,3-5minutes rest shouldbeprescribbetween setstoallowforconsistencyinrepetitions wiout large reductionsinthe training intensity. Conversewhen testing for maximal strength, 1-2 minutes rmightbesufficient between repeated attempts. Anotimportant factor toconsider with regard tosubmaximintensity lifts iswhether setsareperformed tofailuresetsare notperformed tofailure, then 1-2minutes rmight be sufficient because of reduced metabolic deman

When trainingformuscular power, longer rest intvalsaregenerally prescribed toallowforgreater neulogical recoveryandconsistencyinmovement mechanThe applicable research conducted todate indicates twhen performing repeated maximal-effort moveme(e.g., plyometric jumps), a minimum of 3 minutes rshould be prescribed between sets to maintain powConversely, when performing single maximal-effmovements, such as those used to test for power (eIRM power clean),1-2 minutes rest might be sufficibetween repeated attempts, becauseofrapid resyntbeof intramuscular phosphagens.

When training for muscular hypertrophy, maintaintraining intensityis not theprimary focus,andconsetive sets shouldbeperformed priortowhen full recovehas taken place. A combination of moderate-intensity swith short rest intervalshasbeen demonstratedtobeperiorforhypertrophy training. This might be becauserepeated acute exposure to high levels ofgrowthhmone. Keoghet al. (11)advocated the"breakdown"proach when training for hypertrophy. With this a


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REST INTERVAL 98proach,thefirstset isperformed at arelatively highin-tensity (e,g., 85^^ofIRM), and then the intensityisgrad-ually reduced over subsequent setstosustain consistentrepetitions, with 30-60 seconds rest between sets.

When trainingformuscular endurance, the extremelyshort rest intervals between sets necessitate lowering thetraining intensity over consecutive setstosustain repe-titions within therange conducive tothis training goal.Therefore, achievingahigh training volumeismoreim-portant than sustaining training intensity. However, con-sistent training with short rest intervals mayresultinadaptations that allow training intensity to be sustained.The ideal strategy for increasing muscular endurancemightbe toperform exercisesin acircuit, while alternat-ing exercisesfor theupper and lower body. Using thisstrategy, shorter rest intervals (e.g.,30seconds)arepre-scribed between consecutive exercises that involve mus-clesindifferent regionsofthe body,andlonger restin-tervals (e.g.,3minutes)areprescribed between exercisesthat involve musclesin thesame regionsofthe body.RECOMMEND TIONS FOR FUTURE RESE RCH

Some key factors that havenotbeen examined regardingrest interval length include exercise order withinawork-out, musele fiber composition,and anactive vs.apassiverecovery between sets. Prior studies demonstrated reduc-tionsintotal repetitionsandtraining intensity whenre-sistance exercises were performed last vs. firstin awork-out (24, 25).Therefore, future research should be con-ductedtodetermine whether longer rest intervals are ad-vantageousforexercises performed last in aworkouttoincrease total repetitions and maintain training intensity.A prior study demonstrated that fast-twitch musclefibers were more susceptible tofatigue vs.slow-twitchmuscle fibers, possibly becauseoffaster turnover of Ca 'and ATP inconnection with muscular contraction,and

ATP production via anaerobie processes. Individuals witha higher proportion offast-twitch muscle fibers wereca-pableofgreater force production,butwere less capableof sustaining force production over extended periodsoftime (28). Therefore, future research should be conductedto determine whether individuals with ahigher propor-tion of fast-twiteh muscle fibers require longer rest inter-vals between sets when trainingformaximal strength.Finally,aprior study demonstrated less reductioninrepetitions with an active recovery (stationary cycling45 peak Vo )vs. a passive recovery between sets(9).However, this study examined eonseeutive sets performedatasingle training intensity (e.g., 65 ofIRM)andsub-jects consisted ofuntrained men.Therefore, future re-

search shouldbeconductedathigher training intensitieswith trained men, and long-term strength gains resultingfrom workouts that involve eitheranactiveor a passiverecovery between sets shouldbecompared.R F R N S

1, A u n K S S E M K l ) , D., P. D U C H E , C, H A U T I B R G . POUMAEiAT,ANDM, BEDU. Effect ofrecovery duration onmuscu lar powerandblood lactate during thebench press exercise.Int. J. SportsMed. 20:368-373,1999.2, AM ER IC AN C OL L EG E OK S P OR TS M E DIC IN E .Position stand: Pro-gression modelsinresistance trainingfor healthy adults .Med.Sci. Sports Exerc.34:364-380. 2002,3, ANDERSON, T . ,ANU J . T. KEARNEY, Effects ofthree resistancetraining programson muscular strength andabsoluteand rel-

ative endurance.Res. Q. Fxerc. Sport. 53:1-7 . 1982.

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a brief review, factors afeecting the length

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