Journal of Strength and Conditioning Research, 2006, 20(3), 492-499© 2006 National Strength & Conditioning Association

DYNAMIC VS. STATIC-STRETCHING WARM U P : THEEFFECT ON POWER AND AGILITY PERFORMANCE

DANNY J. MCMILLIAN,' JOSEF H, MOORE,^ BRIAN S, HATLER,^ AND DEAN C. TAYLOR^

'U.S. Army MEDDAC, Heidelberg, Germany; 'U.S. Army-Baylor University Doctoral Physical Therapy Program,U.S. Army Medical Department Center and School, Fort Sam Houston, Thxas 78234; -'Keller Army CommunityHospital,'West Point, New York 10996.

ABSTRACT. McMillian, D.J., J.H. Moore, B.S. Hatler, and D.C.Taylor. Dynamic vs. static-stretching warm up: The effect onpower and agility performance. J. Strength Cond. Res. 20(3):492~499. 2006.—The purpose of this study was to compare the effectof a dynamic warm up (DWU) with a static-stretching warm up(SWU) on selected measures of power and agility. Thirty cadetsat the United States Military Academy completed the study (14women and 16 men. ages 18-24 years). On 3 consecutive days,subjects performed 1 ofthe 2 warm up routines (DWU or SWU)or performed no warm up (NWUl. The 3 warm up protocols last-ed 10 minutes each and were counterbalanced to avoid carryovereffects. After 1-2 minutes of recovery, subjects performed 3 testsof power or agility. The order ofthe performance tests (T-shuttlerun, underhand medicine hall throw for distance, and 5-stepjump) also was counterbalanced. Repeated measures analysis ofvariance revealed better performance scores after the DWU forall 3 performance tests ip < 0.01), relative to the SWU andNWU. There were no significant differences between the SWUand NWU for the medicine ball throw and the T-shuttle run, butthe SWU was associated with better scores on the 5-Htep jump(p < 0.01). Because the results of this study indicate a relativeperformance enhancement with the DWU. the utility of warmup routines that use static stretching as a stand-alone activityshould be reassessed.

KEY WORDS, flexibility, performance testing, conditioning, cal-isthenics

INTRODUCTION

I re-exercise warm up routines are common prac-tice, despite limited scientific evidence support-ing one protocol over another. For this reason,warm up protocols tend to reflect the experi-ence of individual coaches, trainers, and ath-

letes. Traditionally, static-stretching exercises have beena prominent feature of warm up routines {6, 34, 37). Sup-port for a more dynamic warm up (DWU) has grown inrecent years, because several investigations have shownthe potential for acute, static stretching to degrade per-formance on vertical jumps, short sprints, tasks requiringmaximal voluntary contractions, muscle strength-endur-ance performance, balance challenges, and reaction time(2, 3, 6, 10, 11, 20, 21, 23, 27, 37). Additionally, severalstudies now indicate that pre-exercise static stretchingdoes not offer the presumed benefit of injury risk reduc-tion (5, 14, 17, 26, 30).

Smith (32) indicated that the general purpose of a pre-exercise warm up is to increase muscle and tendon sup-pleness, to stimulate blood flow to tbe periphery, to in-crease body temperature, and to enhance free, coordinat-ed movement. Professionals in the strength and condi-tioning community have increasingly touted variousDWUs as the best way to prepare athletes for the physical

demands of their sport (12). Although many variations onthe DWU theme exist, most feature progressive, contin-uous movement. Calisthenics such as squatting and lung-ing movements often are paired with running drills thatinclude forward, lateral, and ch an ge-of-direction move-ment. Investigators have shown DWU to improve kneejoint position sense, to increase oxygen uptake, to lowerlactate concentration and raise blood pH, to improve ef-ficiency of thermoregulation, and to improve performancefor bicycle sprints and vertical jumps (1, 6, 7, 15, 20, 37).

Recently the United States Army Physical FitnessSchool (APFS) developed a DWU for individuals and mil-itary units. The stated objectives are to increase bodytemperature and beart rate, pliability of joints and mus-cles, and responsiveness of nerves and muscles in prep-aration for physical readiness training activities. TbisDWU was used before each exercise session as part of anintervention to decrease injuries and to improve physicalperformance among soldiers in a basic training battalion.Static stretcbing, a prominent feature of tbe warm up forgenerations of soldiers, was not included. Althougb mul-tiple interventions confounded tbe effect of tbe DWU, in-jury rates over tbe 9-week training period were signifi-cantly decreased compared witb botb a control battalionand historic trends. Performance on physical fitness test-ing generally was improved (19).

Given tbe ubiquity of static stretcbing in warm up ac-tivities, tbe purpose of tbis study was to compare tbe ef-fect of a DWU (based on tbe APFS model) witb tbat of astatic-stretcbing warm up (SWU) or no warm up (NWU)on selected measures of power and agility. Dependentvariables to assess power and agility were cbosen, be-cause tbese attributes are common requirements for a va-riety of sports. Tbe DWU protocol in tbis study closelymimicked tbe power and agility requirements of manysports, so we bypotbesized tbat it would result in a per-formance enbancement relative to tbe SWU or NWU.

METHODS

Experimental Approach to the Problem

All subjects attended a 2-part orientation session tbat in-cluded (a) instruction for active participation in botb tbeDWU and SWU and (b) practice of the 3 performancemeasures (i.e., the T-drill, 5-step jump, and tbe medicineball tbrow for distance). Tbe independent variable wastbe type of warm up used before performance testing. Tbedependent variables were tbe scores on tbe 3 performancemeasures. During tbe orientation, subjects were givenfeedback to enbance proper execution of botb tbe warmup tecbniques and tbe performance measures. To ensure

492

EFFECT OF WARM UP PARAMETERS 493

that subjects had mastered the techniques for the perfor-mance measures, they repeated each ofthe 3 events untiltheir scores no longer improved. Rest between trials ofthe T-drill lasted approximately 2 minutes. Rest betweentrials of the 5-step jump and medicine ball throw for dis-tance was at the subject's discretion, but generally of 30-60 seconds' duration. Subjects were encouraged to take aslong as necessary to recover from the previous effort.

SubjectsThirty cadets at the United States Military AcademyfUSMA) volunteered for and completed the study. Sub-jects were recruited from USMA club sports. Cadets wereeligible for the study if they were fit for full military dutywithout restrictions. All subjects completing the studywere members of rugby, lacrosse, or strength and condi-tioning teams. Members ofthe rugby and lacrosse teamswere competing weekly. In addition, all cadets have rou-tine physical requirements. For these reasons, the sub-jects were screened by the primary investigator before thestudy to establish eligibility and before each training ortesting session to ensure continued eligibility. Exclusioncriteria were: (a) acute impairment of the spine or lowerextremities, vestibular dysfunction, or balance disorder,(b) histoiy of surgery in either lower extremity, and (c)history of a neurological disorder affecting the upper orlower extremities. All subjects gave written, informedconsent prior to participation in the study. The mean ±standard deviation iSD) for age, height, and weight forthe 16 men were 20.2 ± 1.2 years, 182.4 ± 6.6 cm, and88.8 ± 9.0 kg, respectively. The mean ± SD for age,height, and weight for the 14 women were 20.4 ± 1.5years, 167.1 ± 7.9 cm, and 64.0 ± 7.8 kg, respectively.All subjects gave written informed consent prior to par-ticipation. The study was approved by the Human Sub-jects Research Review Board of Keller Army CommunityHospital, West Point, NY.

Warm Up ProtocolsSubjects executed the warm up sessions in small groupswith the primary investigator leading the DWU (Table 1)and an associate investigator (BH) leading the SWU (Ta-ble 2). The order in wbich the subjects performed tbe 3warm up conditions was counterbalancecl to avoid poten-tial biasing effects associated with test sequence. Eachwarm up session lasted 10 minutes. Subjects scheduledfor NWU rested in an area adjacent to the testing site.

Performance Testing

Most recent investigations of pre-exercise stretching haveused vertical jump tests as the measure of performance.The present investigation used other performance mea-sures (Table 3) in order to evaluate agility as well as abroader spectrum of tasks requiring power. Care was tak-en to avoid tasks that would induce fatigue, because fa-tigue has been shown to hinder local muscular perfor-mance, especially for tasks that involve the stretch-short-ening cycle.(18)

The 5-step jump was chosen as a measure of function-al leg power. Single-leg hop tasks are used more com-monly as functional tests; however, they are most oftenused to assess symmetry, and therefore normalcy, of thelower extremities following unilateral lesions, such as an-terior cruciate ligament deficiency or reconstruction (9).For our purposes, symmetry was less important than

were aggregate lower body power and stability. Wiklan-der et al. have shown the 5-step jump to be a reliablemeasure that correlates well with the vertical jump, longjump, and isokinetic leg strength (35).

The medicine ball throw for distance was chosen as ameasure of total-body power. Stockhrugger et al. haveshown this test to be a valid and reliable test for assessingexplosive power for an analogous total-body movementpattern and general athletic ability (33).

The T-drill was chosen primarily as a measure of agil-ity. For this test, the component tasks of (a) forward,backward, and lateral running; (b) stopping and changingdirection; and (c) reaching with an upper extremity whilelowering the center of gravity are all representative ofcommonly encountered tasks in sports. Pauole et al. haveshown this test to be a valid and reliable measure of agil-ity, leg power, and leg speed in college-age men and wom-en (25). To emphasize lateral movement, the forward- andbackward-run portions ofthe T-drill were set at 5 m rath-er than the 10-yd distance described by Pauole.

Data collection began the day after the orientationand ran for 3 consecutive days. Subjects performed 1warm up protocol (DWU, SWU, or NWU) before data col-lection eacb day. Subjects were instructed to avoid exer-cise or vigorous physical exertion the morning of testing.All tests were conducted at 6 AM at the same test siteeach day.

After completing 1 of the warm up conditions (or 10minutes of rest for the NWU group), subjects proceededto the performance testing stations. The time betweenfinishing the warm up and beginning the performancetesting was approximately 2 minutes. The order of testingwas counterbalanced to avoid carryover effects. A physi-cal therapist or physical therapy assistant who was un-aware of the subject's group assignment scored each per-formance test. None of the investigators participated indata collection. The primary investigator then compiledall data for analysis.

Attempts were made to control potentially confound-ing variables. For example, (a) testing occurred at 6 AMeach day, with subjects advised not to eat or drink any-thing other than water before testing; (b) subjects werequeried for injuries, illness, or excessive fatigue each day;(c) subjects were reminded ofthe importance of maximaleffort each day before testing; (d) gi'aders were eitherphysical therapists or pbysical therapy assistants with atleast 1 year of experience collecting peiformance mea-surement data for another study: and (e) graders receiveda standardized orientation to the measurements requiredfor the study.

Ten subjects were removed from the study after com-pleting the orientation: 2 subjects for excessive fatiguefrom cadet physical requirements the previous day, 2 sub-jects from injuries related to military training, and 6 sub-jects for missed testing sessions. No subjects were injuredduring the performance of either of the warm up condi-tions or performance testing.

Statistical Analyses

Pre hoc power analysis was used to establish the appro-priate sample size, based on the following parameters:effect size ^ 0.27 (based on previously reported data onthe 5-step jump 1351), 3 degrees of freedom, power = 0.80,and alpha = 0.05. Repeated measures (2 [gender] X 3Iwarm up protocol!) analysis of variance (ANOVA) was

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TABLE 4. Performance on each dependent variable based onwarm up conditions (A'' - 30). Data are mean ± SD.*

T-drill (8)

Medicine ballthrow for

distance (m)5-step jump

(m)Control (NWU)swuDWU

9.77 ± 0.829.69 ± 0.859.56 ± 0.79t

9.47 ± 2.899.34 ± 2.879.79 ± 3.01t

9.51 ± 1.141:9.78 ± 1.172:1:

10.06 ± 1.231:

* NWU = no warm up; SWU = static-stretching warm up;DWU = dynamic warm up.

t Denotes significant difference from the other 2 warm up con-ditions (p < 0.01).

t Denotes significant difference between all 3 warm up con-ditions (p < 0.01).

used to evaluate the effect of warm up conditions on the3 performance measures. Tukey's honestly significant dif-ference (HSD) was used for post hoc analysis. Statisticalsignificance was set at p ^ 0.05.

RESULTS

Descriptive statistics representing the performance oneach dependent variable based on warm up conditions arepresented in Table 4. Repeated measures ANOVA re-vealed neither a significant main effect nor interaction forgender; therefore, data were collapsed for post hoc test-ing. The main effect for warm up protocol was significant.Pair-wise comparisons using Tukey's HSD revealed thatsubjects scored better after the DWU than after the NWUor SWU on all 3 performance tests ip < 0.01). There wereno significant differences between the SWU and NWU forthe medicine ball throw and the T-drill; however, subjectsscored better after the SWU than after the NWU on the5-step jump (p < 0.01).

DISCUSSION

The purpose of this study was to comp£ire the effects ofDWU, SWU, and NWU on selected measures of powerand agility. Results indicate that the DWU conferred amodest performance enhancement for all 3 measures ofpower and agility relative to the SWU and NWU. Theseresults are consistent with Bishop's review of the litera-ture, indicating that an active warm up of moderate in-tensity is likely to significantly improve short-term per-formance on a range of tasks as long as fatigue is notinduced (4). Although static-stretching warm up exerciseshave been shown to decrease power and one-repetitionmaximum strength tasks (21, 37), our results show nosignificant difference between tbe SWU and NWU for theT-drill and the medicine ball throw for distance. TheSWU was a significant improvement over NWU for the5-step jump.

In a review of the warm up literature. Bishop citesseveral reasons why an active warm up such as the DWUused in this study might improve short-term performance(4). Most factors are related to temperature and includedecreased stiffness of the muscles and joints; increasedtransmission rate of nerve impulses; changes in tbe force-velocity relationship; and increased glycogenolysis, gly-colysis, and high-energy phosphate degi-adation. In ad-dition to these temperature-related changes, 2 neuromus-cular phenomena possibly activated by the DWU couldpotentially enhance power and agility performance. Post-activation potentiation (PAP; an increase in muscle

EFFECT OF WARM UP PARAMETERS 497

twitch force and rate of force development following a con-ditioning contractile activity) could theoretically improvepower and agility performance, though the optimal pa-rameters to exploit PAP are unknown (29). Similarly, po-stcontraction sensory discharge (increased neural activitymeasured in the dorsal roots following contraction) migbtenable a more rapid and forceful response to perturba-tions of muscle lengtb (8). Active warm up also may de-crease muscle stiffness by breaking the stable bonds be-tween actin and myosin filaments, though stretching like-ly has tbe same effect (4, 34).

Altbough none of tbe physiological factors mentionedabove were measured directly, we believe that the de-mands of the DWU used in this study are generally con-sistent with the recommendations of Bishop (4). For en-hancement of short-term performance (10 seconds orless), evidence suggests a warm up of 5-10 minutes, per-formed at 40-60*^ of VOamax, followed by 5 minutes ofrecovery (4). Although the recovery interval used in thepresent study was less than Bishop's recommendation, fa-tigue did not appear to be significant in our athletic sub-jects.

In contrast to the benefits of an active warm up men-tioned above, tbere are at least 2 theories why pre-exer-cise stretching might decrease subsequent performancerelative to a more dynamic warm up. First, several re-searchers bave cited reduced neural activation as ameans by which repeated stretches reduce the number ofmotor units available for contraction (3, 11, 21). If theSWU reduced neural activation relative to the DWU, per-formance of power and agility tasks, such as those usedin this study, might be diminished. Because neural acti-vation was not measured, its effect on tbe performancemeasures used in this study is purely speculative.

In addition, other investigators have suggested thatincreased compliance (i.e., the lengtb change that occurswhen a force is applied) in the tendon results in a briefmoment when muscle force is taking up slack within thetendon, rather than contributing to gross movement (14,21). Potentially, such an effect could binder power andperformance. However, some studies have shown in-creased joint range of motion without changes in the com-pliance of the musculotendinous unit {16, 22), suggestingthat greater stretch tolerance migbt account for tbe in-creased range of motion. Taylor et al. bave sbown thatstretching and isometric contractions both result in sub-sequent relaxation of tbe muscle-tendon unit (34). Thisconcept is supported by a clinical study in which 3 differ-ent warm up conditions (i.e., body-weight circuit exercis-es, static stretching, and proprioceptive neuromuscularfacilitation stretching [PNFJ) each resulted in equivalentincreases in hamstring flexibility (6). This suggests thata dynamic warm up might increase fiexibility from tberesting state without the potential compromise of neuralactivation associated with an isolated, static-stretchingwarm up.

It is important to distinguish between pre-exercisestretching and flexibility training in general. The perfor-mance-related issues from pre-exercise stretching men-tioned above, especially reduced neural activation, mightnot apply to stretching exercises performed at othertimes. In fact, investigations have noted improved perfor-mance correlated to regular stretching (31) and increasedfiexibility (36). Gleim et al., in a review of the literatureon flexibility and sports performance, noted the sport-spe-

cific nature of fiexibility, suggesting that flexibility train-ing might enhance performance in sports tbat rely on ex-tremes of motion for movement. Conversely, decreasedflexibility migbt actually increase economy of movementin sports such as distance running, where only the mid-portion of tbe range of motion is used (14). Tbe evidencesuggests that flexibility training sbould be applied, basedon individual needs and the physical demands of the ac-tivity.

Although tbe current investigation examined only theeffect of warm up parameters on performance, injury pre-vention is cited routinely as a reason for pre-exercisewarm up. As reported by Shrier (30), the recent epide-miological evidence suggests typical pre-exercise musclestretching protocols do not produce meaningful reduc-tions in risk of exercise-related injury. Conversely, basicscience supports the notion tbat an active warm up mightprotect against muscle strain injury, thougb clinical re-search is equivocal on this point (14). Theoretically, warmup activities that enhance neural activation will betterprepare muscles to absorb loads that might otherwise betransmitted to otber structures such as ligaments, ten-dons, and tbe muscle cytoskeleton. This concept is sup-ported by research sbowing that muscles under activecontraction absorb significantly more energy than mus-cles at rest (13). Recently, Olsen et al. were the first touse a large, randomized, controlled study to show reducedrates of injury in a group performing a dynamic, func-tional warm up (24).

The following factors should be considered when in-terpreting the results of tbe present investigation. First,due to study design and restriction on tbe availability ofsubjects, only 3 repeated measures (one eaeh followingDWU, SWU, and NWU) were conducted. Therefore, thecombined effect of dynamic and static stretching warm upcomponents was not tested. Few studies have examinedthe effect of pre-exercise stretching combined with a dy-namic component. Church et al. compared the effect of ageneral warm up consisting of a 10-minute circuit of body-weight exercises with the same warm up paired witb ei-ther static-stretching or PNF stretches (6). Vertical jumpperformance was limited only by tbe PNF stretch warmup. The investigators theorized that the increased inten-sity of the PNF stretching might induce autogenic inhi-bition and, therefore, might limit vertical jump perfor-mance.

Rosenbaum et al. found that decreased force and rateof force development related to stretching was returnedto normal after 10 minutes of running (28). This suggeststbat pre-exercise stretching may not hinder power per-formance if followed by dynamic movements tbat mimicthe tasks that follow. Warm up protocols that combinedynamic and static-stretching exercises would add com-parative value and are encouraged for future investiga-tions. Still, for teams and individuals that are under timeconstraints for warm up, the current body of evidencesuggests that static stretching might be unnecessary.

Another limiting factor of this study is that physiolog-ical parameters of the warm up protocols were not estab-lished. Controlling for factors such as muscle temperatureand oxygen utilization would have allowed for greaterprecision when describing warm up parameters. Cautionshould be used when generalizing the results of this studyto other populations. Our subjects were young athletesaccustomed to vigorous athletic and military training;

498 McMll.T.IAN ET AI-

older or less-athletic populations migbt respond differ-ently to the warm up protocols used in this study.

Though evidence from previous investigations allowsus to make general recommendations for the specificity,duration, intensity, and recovery interval of the warm up(4), questions remain as to tbe optimal parameters fortbese factors. Future clinical research should continue toinvestigate not only the optimal warm up parameters forduration, intensity, and recovery interval, hut also theinterplay of dynamic and static stretching components,sports specificity, environmental conditions, and psycho-logical factors. In addition, more investigations are need-ed to establish the optimal warm up conditions for injurycontrol.

PRACTICAL APPLICATIONS

For tasks requiring power and agility, the results suggestthat a dynamic warm up might offer performance benefitsnot found with static stretching or no warm up. It is likelythat a DWU similar to that used in this study will achievegeneral warm up goals without invoking tbe mechanicaland neural activation drawbacks associated with acute,static-stretching. For tasks demanding a high degree offlexibility, power, and agility, warm up activities shouldbe sequenced so that static-stretching (if it is deemed nec-essary) is followed by dynamic, progressive movementsthat mimic the goal activity without inducing fatigue.

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AcknowledgmentsThe authors would like to thank Lieutenant Commander MikeRosenthal, Captain Marc Weishaar, Captain Erin Slivka, andStaff Sergeant William Woodside for their assistance with data

coUection; Lieutenant Colonel Paul Stoneman for review of themanuscript; and reference librarian Joan Stehn.

This study was conducted at the United States MilitaryAcademy, West Point, by the U.S. Army-Baylor University Post-Professional Sports Medicine-Physical Therapy DoctoralProgram.

Dificlaimer: The opinions and assertions contained herein arethe private views ofthe authors and are not to be construed asofficial or as reflecting the views ofthe Department ofthe Armyor Department of Defense.

Address correspondence to: Danny J. McMillian,danny.mcmillian@us.army.mil.