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  T HE  I MPACT OF  D IFFERENT  W  ARM - UP  P ROTOCOLSON  V  ERTICAL  J UMP  P ERFORMANCE IN  M  ALE C OLLEGIATE  A  THLETES B RADY   W. H OLT 1  AND  K   ATE  L  AMBOURNE 2 1 Strength and Conditioning Athletic Department, University of Evansville, Evansville, Indiana;   2  Kinesiology Department,University of Georgia, Athens, Georgia   A  BSTRACT The purpose of this study was to compare the impact ofdifferent types of warm-up on countermovement vertical jump(VJ) performance. Sixty-four male Division I collegiate footballplayers completed a pretest for VJ height. The participants werethen randomly assigned to a warm-up only condition, a warm-upplus static stretching condition, a warm-up plus dynamicstretching condition, or a warm-up plus dynamic flexibilitycondition. VJ performance was tested immediately after thecompletion of the warm-up. The results showed that there wasa significant difference ( P   ,  .05) in VJ performance betweenthe warm-up groups. Posttest jump performance improved in allgroups; however, the mean for the static stretching group wassignificantly lower than the means for the other 3 groups. Thestatic stretching negated the benefits gained from a generalwarm-up when performed immediately before a VJ test. K  EY   W ORDS  power output, static stretching, dynamic stretch-ing, dynamic flexibility I NTRODUCTION  A  thletes typically perform a warm-up to prepare toengage in practice or competition. Traditionally,these warm-ups have included some form of staticstretching. However, there is some evidence thatstatic stretching can be detrimental to the power componentof athletic performance. Stretching has been shown to inhibitdrop-jump performance (16,17), vertical jump performance(2,5,6,7), power output as measured by maximum voluntarycontraction force (3), and leg extension power (15). Themechanisms by which static stretching impairs performanceare unknown, but it has been hypothesized to be related tolower levels of musculotendinous stiffness (14), a reducedability to recruit motor units (4), or the inhibition of the acuteresponse of muscle proprioceptors, such as the Golgi tendonorgans (8).The observation of performance decrements from staticstretching has led to the investigation of alternative optionsfor sport preparation. One such alternative is a dynamicwarm-up, which incorporates movements similar to thoseperformed in the sport (1). Dynamic warm-ups have beenshown to increase power output when cycling (12). Anotheroption that has been suggested for warm-up is dynamicstretching, which is performed to increase dynamic flexibility.Dynamic flexibility stretching consists of performing move-ments that take the limb through the range of motion bycontracting the agonist muscle, allowing the antagonistmuscle to relax and elongate (9,10). A study by Yamaguchiand Ishii (15) compared dynamic stretching to staticstretching and found that leg extension power was greaterafter dynamic stretching. These methods of warm-up maydiffer in the way they affect the non-contractile componentsof the muscle and may not inhibit power performance in thesame manner as static stretching.The purpose of the present study was to compare theimpact of these different warm-up protocols onpower outputin Division I male collegiate football players. Based on theresults of previous research, it was hypothesized that a staticstretching warm-up would not benefit power output asmeasured by VJ performance when recovery time for theelastic component of the muscle was not permitted. Also,a dynamic warm-up and a dynamic flexibility stretching routine were expected to lead to better VJ performance thanstatic stretching because the same power decrements havenot been found with these warm-up methods. This is impor-tant because an appropriate warm-up is critical to successfulperformance in sports such as football. It is also important todetermine whether static stretching immediately prior topower performance is detrimental, because power output isa key component in athletic performance (13). M ETHODS Experimental Approach to the Problem This study was a between-subjects control-group designintended to examine the effects of 4 different warm-ups on VJperformance. Sixty-four participants completed a general Address correspondence to Brady Holt, 1533-4287/22(1)/226–229 Journal of Strength and Conditioning Research   2008, National Strength and Conditioning Association  226  Journal of Strength and Conditioning Research the  TM  warm-up and were then randomly assigned to a warm-upgroup. One group completed no further activity beforecompleting the posttest to examine the effects of a generalwarm-up and to provide a control for comparison. The 3other groups completed 1 of the following types of warm-up:a dynamic warm-up, dynamic stretching, or static stretching.The impact of these warm-ups was assessed via VJ perfor-mance and the scores were analyzed using a repeated mea-suresanalysisofcovariance(ANCOVA)withpretestscoresasa covariate. Subjects Prior to conducting this study, a pilot test with 4 athletes wasperformed to refine and clarify the instructions given to theparticipants. The results of this test were used to determinea sample size with adequate power to detect differencesbetween the groups with a power level of 0.80. Therefore,a total of 64 players from a National Collegiate AthleticsAssociation Division I football team were recruited toparticipate in this study. The participants ranged in age from18 to 25 years (mean 6 SD   data were 20.7  6 1.8), and hada mean weight of 99.69  6  21.41 kg. The participants werefamiliar with the VJ procedure.This study was approved by the University’s InstitutionalReview Board, which required the participant to sign aninformed consent form prior to taking part in the study. Procedures Each participant completed a pretest countermovementvertical jump followed by a 5-minute general cardiovascularwarm-up. The participants were then randomly assigned to 1of 4 groups using a block randomization procedure to creategroupsofequalnumber.OnegroupcompletedtheposttestVJwith no further warm-up. The participants in the 3 othergroups completed the posttest VJ after participating in a staticstretching condition, a dynamic warm-up, or a dynamicstretching warm-up. Participants in all conditions wereallowed to get a drink of water immediately after completing the general warm-up. The posttest vertical jump was perfor-med immediately after the completion of the warm up ineach group.The participants in each condition were tested oncountermovement VJ height using the Vertec Vertical JumpTester (Sports Imports, Hilliard, OH). The countermovement jump was calibrated based on the height of each participant’sstanding one-arm reach. The participants jumped from bothfeet with no step in an attempt to touch the highest vanepossible. Jump height was calculated by adding the amountof vanes reached by the participant to the reference line.Participants continued to jump as long as the jump heightcontinued to increase, until 2 jumps in a row did not resultin touching a higher vane. The highest jump height wasrecorded and used in the analyses. General Warm-Up.  Cardiovascular activity for the duration of 5 to 10 minutes is considered an effective general warm-updue to an increased temperature in the muscles, increasedheart rate, and increased blood flow (7). Increased temper-ature in the muscles allows for a greater amount of flexibility,which prepares the athlete for the movement demands of theactivity, and an increase in heart rate and blood flow deliversoxygen and other necessary nutrients to the muscles to useduring the activity (1).In this study, the general warm-up consisted of 5 minutesof treadmill running. The participants began by running 1minute at 4 miles per hour, and increased the speed by 1 mileper hour each minute for 4 more minutes. Once the generalwarm-up was completed, the participants in the warm-uponly group completed the posttest. Static Stretch Warm-Up.  The participants who were assignedto the static stretch condition completed 5 passive stretcheswith assistance from one of the investigators. The stretcheswere similar to those used in previous research (15) and wereaimed at targeting the muscles involved in performing thecountermovement VJ; which include the hamstrings, thegluteals, the lower back, the quadriceps, and the hip flexors.The stretches were held 3 times to the point of slightlypainful yet tolerable muscle discomfort for the duration of 5seconds with rest intervals of 1 second. It is generally recom-mended that stretches are held longer than this, however,this was the amount of time that the participants typicallyheld stretches prior to activity and this time interval wasselected to mimic those conditions.To stretch the hamstrings, the participant lay on his back andliftedoneleg,keepingitstraightastheinvestigatormovedthe leg toward the head. The gluteal stretch was also done ina supine position, with one leg flexed at the knee and crossedoverthefrontofthebody.Theinvestigatorassistedthisstretchby placing his hands on the participant’s knee and ankle andpushingthelegtowardtheparticipant’shead.Thequadricepsand hip flexors were stretched with the participant lying on his side with the top leg flexed at the knee, and theinvestigator moved the heel toward the gluteals. The lowerback was stretched with the participant lying in a supineposition with the experimenter holding both of theparticipant’s ankles and lifting the legs toward the ceiling.Also, while lying on his back, the participant lifted both legstowardtheceilingwithaslightbendinthekneeandflexioninthe ankle. The investigator assisted this stretch by placing hisbodyontheparticipant’sfeetandleaningforwardtoapplyhisbody weight. Dynamic Warm-Up.  The dynamic warm-up involved perform-ing 10 walking lunges, 10 reverse lunges, 10 single-leg Romanian dead lifts, and 10 straight leg kicks with eachleg. The participants in this group also completed highknees and reverse high knees over a distance of 10 yards.These movements are similar to the movements used insport, and were selected because the participants were accus-tomed to them as they were a part of their normal warm-uproutine. VOLUME 22 | NUMBER 1 | JANUARY 2008 |  227  Journal of Strength and Conditioning Research the  TM |  Dynamic Flexibility.  The dynamic flexibility routine involvedperforming 10 repetitions on each leg of 8 different move-ments: standing front leg swings, standing lateral leg swings,leg scissors to the front and to the side (inverted supineposition, resting on shoulders and elbows), eagles (supineposition), scorpions (prone position), donkey kicks (from theknees), and lateral leg swings (from the knees). The move-ments selected were intended to warm up the muscles usedto perform a vertical jump by engaging the agonist andantagonist muscles. Statistical Analyses An intraclass reliability coefficient (ICC) for the vertical jumpscores was calculated to examine the test reliability of thevertical jump scores. A 1-way analysis of covariance(ANCOVA) was used to determine if significant differencesexisted on the posttest scores across conditions after thegroups were equated on the pretest scores. Therefore, thepretest scores were used as the covariate in the analysis.Fisher’s least significant difference post-hoc tests were usedto investigate significant differences between the groups.A result was considered statistically significant if   P   #  .05.Statistical analyses were performed using SPSS 11.0 (SPSS,Inc., Chicago, IL). R  ESULTS The initial sample consisted of 64 participants, but wasreduced to 63 after the exclusion of one outlier. The groupmeansfor thepretest andtheposttest canbe foundinTable 1.The overall intraclass correlation coefficient (R) for thismeasure was 0.984 with a lower bound of 0.974 and an upperbound of 0.990.Pretest vertical jump scores were not equivalent betweenthe groups; therefore, an ANCOVA was selected to performthe analysis to adjust the posttest scores for initial pretestdifferences. A Cohen’s d measure of effect size was calculatedfor each group using the group’s posttest score, the pretestscore for the entire sample, and a pooled standard deviationfor the groups in the form of mean square error. Thesemeasures of effect size can also be found in Table 1.The assumptions associated with ANCOVA with regardto linearity, normality, and homogeneity of regression slopeswere met. However, the assumption of homogeneity of variance across groups was violated.The posttest VJ means of all 4 groups were higher than thepretest means; however, the VJ height gain in the staticstretching group was significantly less than the gain in theother 3 groups. This can be seen in Figure 1.Using these adjusted marginal means, the ANCOVA wasstatistically significant, (ANCOVA  P   = .001). The warm-upcondition accounted for 23.6% of the variance in the posttestwhen holding constant for the pretest (ANCOVA  h 2 = .236).The coefficient of determination for this model was .955(ANCOVA R 2 =.955), thus the rate of error was approx-imately 4.5%.The Fishers least significant difference post-hoc test wasused to evaluate pairwise differences among the adjustedmeans. There were significant differences in the adjustedmeans between the static stretching group and the othergroups. However, there was no statistically significantdifference between the general warm-up, dynamic warm-up, and dynamic stretching groups. D ISCUSSION The purpose of this study was to determine the effects of 4different warm-ups on power output as measured by vertical jump test performance. The effects of static stretching wereof particular interest, because past research has indicated thatstatic stretching may have detrimental effects on poweroutput. The main finding was a significant improvement invertical jump performance following a general warm-up-onlycondition, a general warm-up plus dynamic warm-up con-dition, and a general warm-up plus dynamic flexibility con-dition. However, no statistically significant improvement wasfoundin thegeneral warm-up plusstatic stretching condition.These results are consistent with the growing body of evidence that static stretching can inhibit a muscle’s maximalpoweroutput(6,14,16),and were in support of the hypothesisthat static stretching would not benefit vertical jumpperformance.There was also support for the hypothesis that the dyna-mic warm-up and dynamic stretching conditions wouldhave positive effects on performance. There were no sta-tistically significant differences between the general warm-uponly group, the general warm-up plus dynamic warm-upgroup, and a general warm-up plus dynamic flexibilitygroup; however, the measures of effect size for each grouprevealed that the dynamic warm-up and dynamic flexibilitywarm-upledtobetterperformancethanthegeneralwarm-upalone.Although the exact mechanisms by which static stretch-ing elicits decrements in power performance are not known,several possibilities have been suggested. Researchers haveposited that stretching may reduce musculotendinousstiffness, which inhibits the production of force in the con-tractile component of the muscle (14). Decreases in forceproduction may also be the result of a reduced ability torecruit motor units as a function of inhibited neural mec-hanisms such as myoelectric potentiation (4). Yet anotherexplanation for decreases in force production is the inhi-bition of the acute response of muscle proprioceptors,such as the Golgi tendon organs or the low threshold painreceptors (8).One factor that was not examined in the present study isthe effects of time on recovery after static stretching. Thisstudy examined the effects of static stretching immediatelyproceeding power performance. With enough time, theelastic components of the muscle may recover but theamount of time necessary for recovery deserves furtherexamination. 228  Journal of Strength and Conditioning Research the  TM Warm-up and Vertical Jump  P RACTICAL  A  PPLICATIONS Although conclusions about the mechanisms responsible fordecreases in power output cannot be drawn from the presentdata, the findings from this study have important practicalapplications. The results of this experiment showed thatwarm-up had an impact on vertical jump performance.However, static stretching appeared to negate the benefits of this warm-up when performed immediately before a vertical jump test. If static stretching can negatively affect perfor-mance on the vertical jump, a skill that demands maximalpower output, it follows that the performance of similarpower skills might be negatively affected if static stretching isundertaken prior to the activity. At the present time, it isrecommended that the hamstrings, gluteals, quadriceps, hipflexors, and lower back are not statically stretched immedi-ately prior to performing a vertical jump if the intent is tomaximize jump performance. If increasing flexibility isa concern, it is recommended that it be developed in a warm-up using dynamic stretching. If static stretching is used,it may be best to delay it until after sport performance.With regard to the dynamic warm-up and the dynamicflexibilityapproaches,itseemsthateitherhasabeneficialeffecton vertical jump performance. However, these approachesmay have the additional benefits such as increasing flexibilityin dynamic movements. Future research might be aimed atthe flexibility-enhancing and injury-preventative aspects of these types of warm-up.  A  CKNOWLEDGMENTS The authors would like to thank Dr. Heath, Dr. DeBerard,Dr. Kras, and Dr. Fargo for their advice on this project. R  EFERENCES 1. Baechle, TR and Earle, RW. Essentials of Strength Training andConditioning (2 nd ed.). Champaign, IL: Human Kinetics, 2000.2. Behm, DG, Bradbury, EE, Haynes, AT, Hodder, JN, Leonard, AM,and Paddock, NR. Flexibility is not related to stretch-induced deficitsin force or power.  J Sports Sci Med   5: 33–42, 2006.3. Behm, DG, Button, DC, and Butt, JC. Factors affecting forceloss with prolonged stretching.  Can J Appl Phys   26: 261–272,2001.4. Bosco, C, Tarkka, I, and Komi, PV. Effect of elastic energy andmyoelectrical potentiation of triceps surae during stretch shortening-cycle exercise.  Int J Sports Med   3: 137–140, 1982.5. Church, JB, Wiggins, MS, Moode, FM, and Crist, R. Effect of warm-up and flexibility treatments on vertical jump performance. J Strength Cond Res   15: 332–336, 2001.6. Cornwell, A, Nelson, AG, Heise, GD, and Sidaway, B. Acute effectsof passive muscle stretching on vertical jump performance.  J Hum  Mov Studies   40: 307–324, 2001.7. Devries, HA. Physiology of Exercise for Physical Education andAthletics. Dubuque, IA: William C. Brown, 1980.8. Moore, JC. The Golgi tendon organ: A review and update.  Am J Occ Therapy   38: 227–236, 1984.9. Murphy, DR. A critical look at static stretching: Are we doing ourpatients harm?  Chiro Sports Med   5: 67–70, 1991.10. Murphy, DR. Dynamic range of motion training: An alternative tostatic stretching.  Chiro Sports Med   8: 59–66, 1994.11. Nelson, AG, Guillory, IK, Cornwell, A, and Kokkonen, J.Inhibition of maximal voluntary isokinetic torque productionfollowing stretching is velocity-specific.  J Strength Cond Res   15:241–246, 2001.12. O’Connor, D, Crowe, M, and Spinks, W. Warm-up exercises and leg power.  J Sci Med Sport   5: 54–60, 2002.13. Wilmore, JH and Costill, DL. Physiology of Sport and Exercise(3 rd ed.). Champaign, IL: Human Kinetics, 2004.14. Wilson, GJ, Murphy, AJ, and Pryor, JF. Musculotendinous stiffness:Its relationship to eccentric, isometric, and concentric performance. J App Physiol   76: 2714–2719, 1994.15. Yamaguchi, Tand Ishii, K. Effects of static stretching for 30 secondsand dynamic stretching on leg extension power.  J Strength Cond Res  19: 677–683, 2005.16. Young, WB and Behm, DG. Effects of running, static stretching and practice jumps on explosive force production and jumping performance.  J Sports Med Phys Fitness   43: 21–27,2003.17. Young, W and Elliot, S. Acute effects of static stretching, pro-prioceptive neuromuscular facilitation stretching, and maximumvoluntary contractions on explosive force production and jumping performance.  Res Q Exerc Sport   72: 273–279,2001. VOLUME 22 | NUMBER 1 | JANUARY 2008 |  229  Journal of Strength and Conditioning Research the  TM |
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