Stretching has long been touted as an important

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1 Journal of Strength and Conditioning Research, 2006, 20(4), National Strength & Conditioning Association BALLISTIC STRETCHING INCREASES FLEXIBILITY AND ACUTE VERTICAL JUMP HEIGHT WHEN COMBINED WITH BASKETBALL ACTIVITY MANDY T. WOOLSTENHULME, 1 CHRISTINE M. GRIFFITHS, 2 EMILY M. WOOLSTENHULME, 1 AND ALLEN C. PARCELL 1 1 Human Performance Research Center, Brigham Young University, Provo, Utah 84602; 2 Nova Southeastern University, Fort Lauderdale, Florida ABSTRACT. Woolstenhulme, M.T., C.M. Griffiths, E.M. Woolstenhulme, and A.C. Parcell. Ballistic stretching increases flexibility and acute vertical jump height when combined with basketball activity. J. Strength Cond. Res. 20(4): Stretching is often included as part of a warm-up procedure for basketball activity. However, the efficacy of stretching with respect to sport performance has come into question. We determined the effects of 4 different warm-up protocols followed by 20 minutes of basketball activity on flexibility and vertical jump height. Subjects participated in 6 weeks (2 times per week) of warm-up and basketball activity. The warm-up groups participated in ballistic stretching, static stretching, sprinting, or basketball shooting (control group). We asked 3 questions. First, what effect does 6 weeks of warm-up exercise and basketball play have on both flexibility and vertical jump height? We measured sit and reach and vertical jump height before (week 1) and after (week 7) the 6 weeks. Flexibility increased for the ballistic, static, and sprint groups compared to the control group (p ), while vertical jump height did not change for any of the groups. Our second question was what is the acute effect of each warm-up on vertical jump height? We measured vertical jump immediately after the warm-up on 4 separate occasions during the 6 weeks (at weeks 0, 2, 4, and 6). Vertical jump height was not different for any group. Finally, our third question was what is the acute effect of each warm-up on vertical jump height following 20 minutes of basketball play? We measured vertical jump height immediately following 20 minutes of basketball play at weeks 0, 2, 4, and 6. Only the ballistic stretching group demonstrated an acute increase in vertical jump 20 minutes after basketball play (p 0.05). Coaches should consider using ballistic stretching as a warm-up for basketball play, as it is beneficial to vertical jump performance. KEY WORDS. warm-up, static stretching INTRODUCTION Stretching has long been touted as an important part of fitness and exercise warm-ups because of its putative effects on injury and performance. However, few controlled studies exist to support the assertion that stretching decreases injury (29). Furthermore, a growing body of evidence indicates that the acute effects of stretching may impair performance, while the chronic effects of stretching on performance are less clear. Because stretching is routinely included as a warm-up for sport participation, the effects of a stretching warm-up in the context of sport performance are an important consideration for coaches and athletes. If stretching does not reduce injury and may impair performance, its inclusion as a warm-up may be unwarranted. Following a single bout of stretching, decreases have been seen in 1 repetition maximum (1RM) knee flexion and knee extension (18, 23), maximal voluntary contraction (11), maximal isometric torque (21), maximal isokinetic torque (5, 8, 22), and balance, reaction time, and movement time (1). Decreases in the strength and power of acutely stretched muscle may contribute to a decrease in vertical jump performance; however, conflicting data exist. Some studies have shown decreases in vertical jump height following static stretching (3, 9, 31, 34) and proprioceptive neuromuscular facilitation (PNF) stretching (2), whereas other studies have shown no decrease in vertical jump height following static stretching (2, 17, 25, 30) and ballistic stretching (30). Few studies have looked at the chronic effect of stretching on performance. Two studies indicate that flexibility training does not improve performance. Running economy did not change following 3 weeks of hip or trunk flexibility training (13) or following 10 weeks of thigh and calf flexibility training (24). Additional evidence from correlation studies provides conflicting data regarding the relationship between flexibility and performance. In elite men volleyball players, greater hip flexibility was positively correlated with vertical jump height; however, in elite women volleyball players, greater hip flexibility was negatively correlated with vertical jump height (19). In contrast, less flexibility was associated with higher running economy in subelite and recreational runners (4, 12). Because the inclusion of stretching as part of a preexercise warm-up is common practice, it is necessary to understand its effects on performance. Both the chronic and acute effects of a stretching warm-up on vertical jump performance are unclear. Furthermore, no studies have investigated the effect of stretching combined with sport participation on vertical jump performance. The purpose of our study was twofold: to investigate both the chronic and acute effects of a stretching warm-up combined with sport participation on vertical jump height and flexibility. Specifically from a coaching standpoint, we wanted to test whether stretching prior to basketball play is beneficial or detrimental to vertical jump performance. Because basketball is a highly anaerobic activity consisting of repeated sprints, we also wanted to evaluate the effects of a more specific warm-up of full-court sprints on vertical jump performance. To this end, we measured flexibility and vertical jump height before and after 6 weeks of a static stretching, ballistic stretching, sprinting, or basketball shooting warm- 799

2 800 WOOLSTENHULME, GRIFFITHS, WOOLSTENHULME ET AL. TABLE 1. Group Control Ballistic Sprint Static Subject characteristics.* Height (cm) Weight (kg) * Values are means SD. Age (y) n Women Men approved by the University Institutional Review Board, and all subjects gave their informed consent. FIGURE 1. Experimental design. Pre- (week 1) and posttest (week 7) vertical jump and sit-and-reach test measurements were not preceded by a warm-up. up that was followed by 20 minutes of basketball play. We also measured vertical jump height every 2 weeks immediately after the warm-up and immediately after basketball play. We asked 3 questions: (a) What is the chronic effect of flexibility training used as part of a warm-up for sport participation on vertical jump height?; (b) What is the acute effect of stretching on vertical jump height?; and (c) What is the acute effect of stretching on vertical jump height when it is combined with basketball play? Based on the studies that have shown decreases in power and strength with stretching, we hypothesized that vertical jump height would decrease with 6 weeks of stretching training that resulted in increased flexibility. We also expected an acute decrease in vertical jump height immediately following the stretching warm-ups that would persist throughout the basketball play. METHODS Experimental Approach to the Problem Subjects participated in 6 weeks (2 times per week) of basketball activity preceded by a warm-up. Subjects were randomly assigned to 1 of 4 warm-up groups. The warmup consisted of 5 minutes of light jogging followed by 8 minutes of either ballistic stretching, static stretching, sprinting, or basketball shooting (control). The warm-up was followed by 20 minutes of basketball play. Vertical jump height and flexibility (sit and reach) were measured before and after the 6 weeks of exercise. Vertical jump height and flexibility measurements were taken on separate days, 48 hours apart during week 1 (pretest) and during week 7 (posttest). No warm-ups were performed on the pre- and posttest days. Vertical jump was also measured every 2 weeks (weeks 0 6) immediately following the warm-up (post warm-up) and immediately following the basketball play (postbasketball) (see Figure 1). Subjects Forty-three subjects (27 women, 16 men) volunteered for this study. All subjects were enrolled in beginning or intermediate basketball physical education classes at the university. All were recreationally active with no formal jump training background. Subject characteristics are reported in Table 1. Subjects were healthy and did not have a history of injury to the lower extremities. The study was Flexibility Flexibility was measured with a sit-and-reach test (2, 18, 23). Subjects removed their shoes and sat in the straight leg position with their feet flat against the sit-and-reach testing box. Subjects placed one hand on the other, with the middle fingers aligned and elbows extended. Subjects reached forward with their hands on top of the sit-andreach box, as far as possible, without bending their knees. The feet were considered as zero, and each subject s score was recorded as the distance from the tip of the middle finger to the feet. Both positive and negative scores were thus measurable. Because we were interested only in the change in flexibility, the data are reported as the difference in flexibility pre- to posttest. The best of 3 trials was used. Vertical Jump Vertical jump height was measured with a jump force plate (Probotics, Inc., Huntsville, AL) that calculated height based on time in the air. Jump heights were measured for a 2-leg, standing take-off, in which subjects first bent their knees and then jumped upward as high as possible. Two trials were performed, with a 5-second rest interval between each trial. Vertical jump height was determined as the best of the 2 trials. Static Stretching Group The static stretching program consisted of 4 stretching exercises. Each stretch was held for 30 seconds. All stretches were performed twice with a 15-second rest between stretches. The following is a description of each exercise. Sit and Reach. Subjects were seated with their legs straight and their feet upright, no more than 6 in. apart. Subjects bent from the waist until they felt tightness but not pain. Lunge Knee Bent. Subjects were standing and were instructed to take a long step forward. The front knee was directly above the ankle, and the other knee was resting on the floor. Without changing the position of the knee on the floor or the forward foot, subjects lowered the front of the hip downward. Standing Heel Cord Knee Extended. Subjects stood on a stair with one ankle off the end of the step and the other on the step. Subjects kept the back leg straight and allowed their weight to push the back ankle down as far as possible without eliciting pain. Standing Heel Cord Knee Flexed. Subjects stood on a stair with one ankle off the end of the step and the other on the step. Subjects bent the back knee and allowed their weight to push the back ankle down as far as possible without eliciting pain.

3 FLEXIBILITY AND VERTICAL JUMP 801 TABLE 2. Vertical jump height (cm).* Group Pretest Posttest Control Ballistic Sprint Static * Values are means SEM FIGURE 2. Change in flexibility after 6 weeks. Values are means SEM. *p , compared to control. Ballistic Stretching Group The ballistic stretching group performed exactly the same exercises as the static stretching group, except that each exercise was performed with end range-of-motion, bouncing movements. A metronome was set to 60 b min 1 and subjects bounced to the beat. Sprint Group The sprint group completed five 35-second sprints the length of the basketball court, with a 30-second rest period in between each sprint. For one 35-second sprint, subjects began on the baseline, sprinted to the near foul line and back, sprinted to the half-court line and back, sprinted to the far foul line and back, and sprinted to the opposite baseline and back. Control Group The control group consisted of a basketball shooting warm-up with a partner. One person shot the basketball from anywhere on the court and then rebounded the ball and passed it to his/her partner. The partner then shot, rebounded his/her own shot, and passed back to the first person, who repeated the cycle until the warm-up period was over (8 minutes). Statistical Analyses The pre- and posttest flexibility and vertical jump data were analyzed with separate 1-way analyses of variance (ANOVAs). To test the acute effects of stretching on vertical jump, the pre- and posttest vertical jump data (no warm-up) were compared to the post warm-up vertical jump and the postbasketball vertical jump with a repeated-measures ANOVA. All individual pairwise comparisons were made with the Tukey post hoc test, and significance was set at p RESULTS Flexibility Flexibility increased significantly for all groups, compared to the control group, after the 6 weeks (Figure 2). The ballistic group increased by cm, the sprint group increased by cm, and the static group increased by cm, (p , values are means SEM). Vertical Jump Height Vertical jump height did not change after 6 weeks for any group, indicating that chronic stretching does not affect vertical jump height (Table 2). Vertical jump height was FIGURE 3. Vertical jump height without warm-up (no warmup), after warm-up (post warm-up), and after warm-up and basketball play (postbasketball). Values are means SEM. * p 0.05, significantly greater than no warm-up for the ballistic group; p 0.05, significantly greater than post warmup for the ballistic group. not different for any group immediately following the warm-up compared to the no warm-up vertical jump group (pre- and posttest data), indicating that stretching does not affect acute vertical jump height. However, for the ballistic stretching group, following 20 minutes of basketball play (postbasketball), vertical jump heights were 2.9 and 3.2 cm greater, compared to post warm-up and no warm-up vertical jump groups, respectively (p 0.05) (Figure 3). DISCUSSION We investigated the effects of a sport-specific warm-up, a sprinting warm-up, and 2 different stretching warm-ups, on flexibility and vertical jump height. We hypothesized that 6 weeks of stretching would decrease vertical jump height. In contrast to our hypothesis, flexibility training had no effect on vertical jump height. This finding is similar to that observed in other studies (13, 24), which indicated that flexibility training does not improve running economy, indicating that increased flexibility associated with chronic stretching has little effect on performance. We also hypothesized that stretching would have an immediate negative effect on vertical jump height. However, vertical jump height was not different in the post warm-up group compared to the no warm-up group. Previous research has reported mixed results with regard to the acute effect of stretching on vertical jump height. Following static stretching, some studies have shown a decrease (3, 9, 31, 34), while other studies have shown no decrease in vertical jump height (2, 17, 25, 30, 35). The authors of one study (30) investigated the effects of ballistic stretching on vertical jump height, and they reported no decrease in vertical jump height. Our results would agree with the growing body of evidence that both static and ballistic stretching may not decrease acute vertical jump height. A recent study by Power et al. (25) reported a decrease

4 802 WOOLSTENHULME, GRIFFITHS, WOOLSTENHULME ET AL. in isometric maximal voluntary force (MVC) of the quadriceps that was not associated with a decrease in vertical jump height following static stretching. Other studies have shown decreases in MVC (11), 1RM knee flexion and extension (18, 23), maximal isometric and isokinetic torque (5, 8, 21, 22), and balance, reaction time, and movement time (1) following various protocols of static stretching. This evidence for decreased muscular performance following stretching may not directly translate into decreased whole-body vertical jump height performance, as seen in our study and other studies. Our third question was to determine the effects of both stretching and basketball play on vertical jump height. We hypothesized that a decrease in vertical jump height immediately following the warm-up would persist after 20 minutes of basketball play. We did not see a decrease after the warm-up, as previously discussed, and we report a 3-cm increase in vertical jump height for the ballistic stretching group following basketball play, compared to both the no warm-up and post warm-up conditions. This is a finding with potentially significant practical application. Using ballistic stretching as part of a warm-up before playing basketball may actually be beneficial to vertical jump performance. The mechanism behind this increase in vertical jump height is not readily apparent. In a study by Young and Behm (35), the effect of various warm-ups on vertical jump was tested. They reported that vertical jump height was greater after a warm-up consisting of only a 4-minute run, compared to a static stretching-only warm-up. When both the running and static stretching were combined into 1 warm-up, vertical jump height was not different from the control. The authors suggest that stretching may have a negative effect on vertical jump performance, while running has a positive effect. When the 2 were combined into 1 warm-up, they may have cancelled each other out, and no change in vertical jump was seen. These findings agree with our findings, in that no change in vertical jump was seen following a warm-up of running and stretching. Furthermore, in the Young and Behm (35) study, when practice jumps were included in the running and stretching warm-up, vertical jump was higher than the run- and stretch-only warm-up. These data indicate that the inclusion of sport-specific activity into a warmup may increase vertical jump. Our data are similar, in that 20 minutes of basketball play combined with ballistic stretching increased vertical jump. It is interesting that ballistic stretching caused an increase in vertical jump following basketball play, while static stretching did not. The dynamic nature of muscle contractions used in most sports, including basketball, seems at odds with the traditionally used static stretch warm-up. Perhaps ballistic stretching provides a more specific warm-up to the muscle, in that most muscular movements associated with basketball are not static stretches of the muscle but rather dynamic contractions preceded by a ballistic-type stretch. Specificity of stretching to subsequent sport movement is supported by Fletcher and Jones (10), who report that a warm-up including static stretching decreased acute sprint performance, while a warm-up including active dynamic stretching increased acute sprint performance. They suggest that the rehearsal of specific movement patterns through dynamic active stretching may increase coordination, which allows the muscle to transition more quickly, and therefore with increased power, from the eccentric to the concentric phase of contraction. Our flexibility results showed a significant increase following the 6 weeks of training for the static, ballistic, and sprint groups. Our results indicate that ballistic stretching is as effective as static stretching for increasing flexibility, and our results agree with those of numerous other studies (6, 7, 14 16, 20, 33). One study (32) has even reported that ballistic stretching was more effective than static stretching at increasing flexibility. Interestingly, the practice of ballistic stretching has been contraindicated in the literature, under the premise that it carries a greater risk of injury (6, 7, 26, 27) and that it results in greater delayed-onset muscle soreness (6). Unfortunately, the statements from these references that have established the idea that ballistic stretching is dangerous are not supported with any scientific evidence. No scientific evidence exists that ballistic stretching actually causes injury, and some evidence indicates that ballistic stretching may result in less soreness than static stretching (28). Our data also indicate that sprinting was as effective as both static and ballistic stretching at increasing flexibility. The sprint group increased in flexibility to the same degree as did both stretching groups. A study by Wiemann (33) reported a significant increase in hip flexion range of motion following 15 minutes of ballistic stretching, static stretching, and stationary cycling. These combined results demonstrate that sport-related activity may increase flexibility to the same extent as stretching. In conclusion, ballistic stretching, static stretching, and sprinting were equally effective at increasing flexibility. Furthermore, when ballistic stretching was included as a warm-up, performance of vertical jump was increased with basketball play. However, an increased flexibility resulting from 6 weeks of stretching had no effect on vertical jump height. These findings indicate that the stimulus imposed upon the muscle with an acute stretch may be very different than the long-term effects of chronic stretching with respect to motor performance. It may not be a long-term increase in range of motion that is the primary benefit of stretching, but rather the acute stimulus placed upon the muscle in a stretching warm-up. PRACTICAL APPLICATIONS Stretching has long been recommended as part of a warm-up for sports participation. The type of recommended stretching has traditionally been a slow stretch that is held at the point of discomfort but not pain, with the oft-repeated Don t bounce warning. Bouncing during stretching is thought to increase the risk of injury while stretching. Yet no evidence exists to support this claim, and our study indicates that ballistic stretching (defined herein as controlled, bouncing movements performed at the end of the range of motion of a stretch) can be safely and effectively used as a warm-up for basketball play. Ballistic stretching is as effective as traditional static or no-bounce stretching at increasing flexibility. Furthermore, ballistic stretching used as part of a warm-up for basketball play increases vertical jump performance. All of the subjects who engaged in a ballistic stretching warm-up and then played basketball increased their vertical jump heights by about 3 cm. We only measured vertical jump height after 20 minutes of basketball play, so

5 FLEXIBILITY AND VERTICAL JUMP 803 it is unclear when the increase may first appear or if it persists until the end of a basketball game, but clearly a 3-cm increase in jump height would be beneficial for as long as it lasts. Therefore, we suggest that ballistic stretching is a safe and beneficial warm-up for basketball activity. Coaches should consider having their players use ballistic (or bouncing) stretching, as it may more closely mimic the muscular movements of basketball activity and thus provide a more specific, and therefore beneficial, warm-up. REFERENCES 1. BEHM, D.G., A. BAMBURY, F.CAHILL, AND K. POWER. Effect of acute static stretching on force, balance, reaction time, and movement time. Med. Sci. Sports Exerc. 36: CHURCH, J.B., M.S. WIGGINS, F.M. MOODE, AND R. CRIST. Effect of warm-up and flexibility treatments on vertical jump performance. J. Strength Cond. Res. 15: CORNWELL, A., A.G. NELSON, G.D. HEISE, AND B. SIDAWAY. 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