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Effects of Acute Static Stretching of the Throwing Shoulder on Pitching Performance of National Collegiate Athletic Association Division III Baseball Players

Haag, Samuel J1; Wright, Glenn A1; Gillette, Cordial M1; Greany, John F2

Journal of Strength and Conditioning Research: February 2010 - Volume 24 - Issue 2 - p 452-457
doi: 10.1519/JSC.0b013e3181c06d9c
Original Research
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Haag, SJ, Wright, GA, Gillette, CM, and Greany, JF. Effects of acute static stretching of the throwing shoulder on pitching performance of National Collegiate Athletic Association Division III baseball players. J Strength Cond Res 24(2): 452-457, 2010-Stretching is a common component of an athletic warm-up even though many studies have demonstrated that pre-event static stretching can decrease strength and power performance. The purpose of this study was to examine the effects of acute static stretching of the throwing shoulder on pitching velocity and accuracy of National Collegiate Athletic Association Division III baseball players. Twelve collegiate baseball players, including 6 pitchers and 6 position players, participated in the study. Each participant completed 2 separate testing protocols over a span of 4-6 days. In the experimental condition (SS), 6 static stretches were applied to the throwing shoulder after an active warm-up. After a rest period of 5-10 minutes, participants were allowed 5 warm-up pitches from a pitching mound. Participants then threw 10 pitches measured for velocity and accuracy. The control condition (NS) followed the same procedure but did not include the 6 static stretches. Testing was conducted in an indoor practice facility during normal team practice. No significant differences were found in average velocity, maximum velocity, or accuracy measures when comparing the SS and NS conditions. These results suggest that acute static stretching of the throwing shoulder does not have a significant impact on baseball pitching performance. Static stretching of the shoulder may be performed during a warm-up before a throwing activity.

1Department of Exercise and Sport Science; and 2Department of Health Professions, University of Wisconsin-La Crosse, La Crosse, Wisconsin

Human Performance Lab, University of Wisconsin-La Crosse.

Address correspondence to Samuel J. Haag, samueljhaag@hotmail.com.

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Introduction

Flexibility is considered to be an important component of fitness and is believed to provide benefits such as improved joint range of motion (ROM) and enhanced muscular performance (25). As a result, static stretching is often performed during an athletic warm-up. Stretching exercises are designed to increase flexibility by inhibiting mechanoreceptor-mediated reflexes and temporarily increasing the length of the musculotendinous unit (MTU). This reflex inhibition may prevent Golgi tendon organs from limiting agonist muscle contraction (25). If joint ROM is increased, the muscle may be able to produce a more forceful contraction. In the case of a kicking movement, a leg with a greater ROM during the kick has the potential to achieve a higher speed at the instant of impact with the ball (35). This effect would be likely for other movements as well. For example, during a baseball pitch, greater ROM in the shoulder joint may allow more force to be generated during the throwing motion before the ball is released (31).

In the case of a baseball pitcher, stretching of the shoulder during a warm-up may improve joint ROM and help increase force production of the muscles involved with the overhand throw. Greater force production in these muscles may lead to a higher pitch velocity, which could provide a competitive advantage. However, stretching-induced changes in MTU compliance could have detrimental effects. Increased MTU compliance may decrease force production due to an altered length-tension relationship in the muscle (22). This decrease in force may diminish throwing velocity. A warm-up is an essential part of a pitcher's preparation before a game, and an effective stretching routine that increases the ability to produce force would be a beneficial component. If acute static stretching did not have a positive effect on throwing performance, it may be unnecessary. If acute static stretching diminished throwing performance, however, its inclusion in the warm-up would be a contraindication.

The effects of acute static stretching on strength and power performance have been measured with a variety of performance variables, including sprinting (10-13,18,21,26,29), agility (10,18,20), vertical jump (3-6,8,10,11,15,17,18,20,28-30,34), knee flexion and extension (2,9,19,23,24,32,33,37), ankle plantarflexion (1,36), and kicking and striking movements (10,11,20,35). In most cases, static stretching resulted in either a significant decrease or no change in performance. Only one study (22) displayed a significant improvement in performance after a bout of static stretching using a cycling power test. Although majority of studies on acute static stretching have focused on stretches of the leg muscles and the effects on lower-body muscular performance, few studies have measured the effects of acute static stretching on upper-body muscular performance variables (10,11,16,20,27). In these studies, upper-body muscular performance was not significantly affected by acute static stretching. One of the studies (16) found that an acute bout of static stretching did not have a significant effect on overhand tennis serve performance, a skill similar to the overhand throw. However, no research has been conducted to measure the impact of acute static stretching of the throwing shoulder on baseball pitching performance.

Because static stretching is still a common component of an athletic warm-up, it is important to determine the effects it may have on overhand throwing performance. Although many studies have measured the effects of acute static stretching on lower-body performance, little focus has been placed on stretching muscles of the upper body. Increased knowledge in this area will help players and coaches decide whether or not an acute bout of static stretching may be included in a warm-up before throwing. Therefore, the purpose of this study was to determine the effects of six 30-second static stretches of the throwing shoulder on pitching velocity and accuracy of National Collegiate Athletic Association (NCAA) Division III baseball players. Based on results from previous studies, it was hypothesized that inclusion of acute static stretching of the upper body in the warm-up would not significantly affect baseball pitching velocity or accuracy.

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Methods

Experimental Approach to the Problem

This study used a counterbalanced design to evaluate the effects of acute static stretching of the upper body on maximal throwing velocity and accuracy. Counterbalance was employed to account for any training effect that may have taken place between test days. Participants prepared for maximal throwing of a baseball using their normal team warm-up with and without added static stretches of the throwing shoulder. Testing was completed during regular team practice over a period of 2 weeks, before the start of the regular season. Two separate test days were spaced 4-6 days apart for each participant.

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Subjects

Twelve members of an NCAA Division III baseball team participated in the study (descriptive statistics are provided in Table 1). At the beginning of the study, the baseball team had already been conducting normal team practice for 3 weeks and the regular season was set to begin in about 5 weeks. Six of the participants were pitchers, whereas the other 6 were position players. All participants were free from injury and were cleared to participate in the study by the coaching staff and athletic trainers. Participants were informed of all procedures, potential risks, and benefits associated with the study and signed an informed consent document before the investigation. The study was approved by the University of Wisconsin-La Crosse Institutional Review Board for Human Subjects.

Table 1

Table 1

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Procedures

Participants completed 2 separate warm-up protocols. The control condition (NS) involved the normal team warm-up, which began with a light 200-m jog. Participants then played catch for 10-15 minutes, beginning with a distance of about 10 m and eventually throwing at distances exceeding 40 m. The experimental condition (SS) followed the same protocol but also included 6 static stretches of the throwing shoulder after the participants had finished playing catch. Once the warm-up protocol was completed, participants rested for 5-10 minutes and refrained from any stretching or throwing activity. After the rest period, 5 practice throws from a synthetic pitching mound were allowed before testing. They then threw 10 pitches from a full windup to a catcher behind home plate located 18.44 m (60.5 ft) away. Participants were instructed to “throw a fastball for a strike” on each pitch. All testing was completed in an indoor facility during normal team practice.

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Stretching

Six static stretches were included in the SS condition. All stretches were performed in a standing position, and 4 of the 6 stretches required the assistance of an athletic training student. Two athletic training students with several years of experience in applying stretches to the shoulder assisted participants with the static stretches. The SS routine consisted of a shoulder horizontal adduction, horizontal abduction, external rotation, internal rotation, flexion, and extension stretch. These exercises were chosen because they stretched the upper-body muscles involved in the overhand throw (31). Each stretch was performed once on the throwing shoulder for 30 seconds at the point of mild discomfort with a rest period of 10 seconds between each stretch. Stretching and rest periods were timed using a stopwatch. The entire static stretching routine was completed in less than 5 minutes.

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Speed and Accuracy Measurements

Throwing velocity and accuracy are 2 skills a baseball pitcher must have in order to be successful. Pitching velocity was measured with a cordless radar gun (The JUGS Company, Tualatin, OR, USA) by the head baseball coach, who was experienced in using this equipment. According to the manufacturer, the device is accurate up to ±0.5 mph. To compute average velocity, the 2 lowest and 2 highest recorded speeds in each test were dropped and the mean of the remaining 6 values was calculated. Maximum velocity was defined as the highest recorded speed of the 10 pitches in each condition. Accuracy was measured by “charting” pitches, a commonly used method to identify the location of the baseball as it crosses home plate. A rectangle on a chart represents the strike zone, and each pitch is marked on the chart by an observer. Pitches judged to be inside the rectangle were counted as strikes, and those outside the rectangle were counted as balls. Accuracy was defined as the number of pitches (out of 10) in each condition that were thrown for strikes. Charting was completed by the researcher, who had 2 years of experience with charting pitches and also had several years of experience as a baseball umpire for a recreational baseball league. The head coach and researcher stood behind the participant while pitches were being thrown to measure velocity (as recommended by the manufacturer of radar gun) and accuracy, respectively.

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Statistical Analyses

Because reliability analysis of the radar gun measurements displayed Cronbach's alpha for intraclass reliability = 0.99, the velocity measurements of the radar gun were determined to be reliable. Due to a power malfunction with the radar gun, velocity measures were recorded for 11 of the 12 participants. Accuracy measures were recorded for all 12 participants. To first determine if any significant differences in velocity performance existed between pitchers and position players, independent sample t-tests were conducted using the mean of the 2 groups for both the NS and SS conditions. A Mann-Whitney U-test was performed to compare the probability distributions of the accuracy scores of pitchers and position players for both the NS and SS conditions.

Paired sample t-tests were conducted to compare average velocity and maximum velocity between the NS and SS protocols. Wilcoxon signed rank tests were used to compare the distribution of the accuracy scores between NS and SS for both pitchers and position players. Statistical significance was set at the p ≤ 0.05 level for all statistical tests. The magnitude of the differences in mean was shown as effect size (ES) (change in mean/SD) and interpreted according to the criteria used by Cohen (7): <0.2 = trivial, 0.2-0.4 = small, 0.5-0.07 = moderate, >0.7 = large.

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Results

Table 2 displays the velocity and accuracy measures for pitchers and position players after both the NS and SS conditions. After comparing pitchers and position players, independent sample t-tests showed no significant differences in either warm-up condition for average velocity or maximum velocity. Because there were no significant differences in velocity measures, the data for pitchers and position players were collapsed into one group for further analysis. Paired sample t-tests showed no significant differences between NS and SS in average velocity or maximum velocity in all participants (see Table 3).

Table 2

Table 2

Table 3

Table 3

A Mann-Whitney U-test displayed no significant differences in accuracy between pitchers and position players after the NS condition, but a significant difference was found between pitchers and position players in the SS condition (see Table 2). Because accuracy performance was significantly different between pitchers and position players, separate Wilcoxon signed rank tests were used to compare the distribution of the accuracy scores between NS and SS for pitchers and position players. When comparing NS and SS, no significant differences were found in accuracy performance of pitchers. Although the effects of SS on accuracy performance in position players were not significantly different, the ES indicates that a practical effect may exist (see Table 4).

Table 4

Table 4

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Discussion

The results of this study demonstrate that 6 different 30-second static stretches of the throwing shoulder did not have a significant effect on pitching performance in collegiate baseball players. This finding supports the original hypothesis. Pitching velocity measures were not significantly altered when static stretching was included after the baseball team's active warm-up. In the SS condition, pitchers were significantly more accurate than position players. Although position players tended to have higher accuracy scores after the NS condition compared with SS, these differences did not reach statistical significance.

The finding that accuracy performance was significantly different between pitchers and position players after an acute bout of static stretching is supported by previous research. Young et al. (35) proposed that experienced participants with well-developed movement patterns would not be significantly affected by acute static stretching. Because pitchers have more experience throwing pitches from a mound, their accuracy should be less affected by acute static stretching than position players. Torres et al. (27) found that acute static stretching of upper-body muscles had no significant effects on medicine ball toss or bench press performance in collegiate field event athletes and suggested that a pre-existing training effect may have been present because the participants in the study were experienced throwers. In contrast, Knudson et al. (16) found no significant differences in tennis serve accuracy between tennis players of varying skill levels after an acute bout of static stretching. In that study, however, all the participants were experienced tennis players, whereas the position players in the present study were not experienced pitchers.

Some studies have shown that pre-event static stretching significantly decreased performance in activities such as sprinting (10,12,13,21) and vertical jump (3,11,29,30,34). These decreases in strength and power performance have often been attributed to increased MTU compliance or changes in neuromuscular properties. Due to time constraints, no data were collected in the present study to address these mechanisms. Because pitching performance was not significantly affected in this study, it may be assumed that any changes in MTU compliance or neuromuscular properties brought on by acute static stretching were not significant enough to affect pitching performance. The rest period between the warm-up and performance testing may have also been a major factor. The rest period in the present study was designed to replicate the amount of time baseball players typically have between the end of the warm-up and beginning of the game. Torres et al. (27) suggested that physiological responses to acute static stretching may dissipate after a rest period of 5 minutes. The present study included a rest period of 5-10 minutes, similar to the rest period allowed by Torres et al. (27). Further research is needed to determine the amount of time needed for acute static stretching-induced physiological responses to fade.

The volume and intensity of static stretching applied to a muscle group can have a significant effect on performance. Several studies have demonstrated that a static stretching volume of only 30 seconds is sufficient for producing a significant increase in joint ROM without significantly decreasing power or strength performance (23,36,37). Not only does a static stretching volume of 1 minute or more significantly decrease strength and power performance but also does not appear to significantly improve joint ROM beyond what is accomplished with 30 seconds of stretching. Although the total volume of static stretching performed in the present study was longer than 30 seconds, each of the 6 static stretches were only performed once. This volume may still be considered relatively low because many muscles are involved and several different actions occur at the shoulder joint during the overhand throwing motion (31).

Studies involving throwing or kicking movements have shown that acute static stretching did not significantly affect performance in a medicine ball toss (10,11,20,27) or football punt (35). Young et al. (35) concluded that short-term changes in flexibility brought on by static stretching would not significantly alter the performance of a skill that involved complex neuromuscular patterns of a number of muscle groups. After finding that acute static stretching did not significantly change overhand tennis serve performance, Knudson et al. (16) suggested that high-speed movements may not be significantly affected by pre-event static stretching. The results of the present study appear to support these positions.

Several limitations existed in the present study. First, only 10 fastball pitches were recorded in each testing condition. Starting pitchers may throw over 100 pitches during an actual baseball game and not all of them will be fastballs. It may be difficult to extrapolate the results of this study to a game situation. Additionally, throwing velocity and accuracy are not the only factors that determine pitching performance. Another limitation of the study was the low sample number. Because performance testing was completed during team practice to simulate a normal pre-game warm-up, fewer subjects were available to participate in the study. Larger sample sizes may have increased the probability of finding statistical significances, especially in accuracy measures. An attempt was made to determine how worthwhile the results of the present study were by using Cohen's ES as recommended by Hopkins (14) when interpreting results of athletic performance research. Small ESs in the results of the present study confirm a lack of a practical effect to go along with the lack of statistical significance seen in throwing velocity in all subjects and accuracy in pitchers. Although throwing accuracy in position players did not reach statistical significance (p = 0.07), a strong ES (ES = 0.94) indicates that a practical effect likely exists when position players throw for accuracy after acute static stretching of the upper body. It may have been useful to measure joint ROM in this study, but previous research (23,36,37) suggests that applying 1 stretch for 30 seconds produces a significant increase in joint ROM. Because each stretch was performed to the point of mild discomfort, the stimulus should have been adequate to produce an acute change in joint ROM.

Last, the static stretching protocol in this study may not have stressed the upper-body muscles enough to significantly affect throwing. The static stretching exercises used in the present study were applied only to the throwing shoulder, but the baseball pitching motion involves movement of the entire body. Wilk et al. (31) explained that the overhand throwing motion involves a kinetic chain, where energy is transferred from the legs and trunk to the throwing arm to execute the movement. Different results may have been found if static stretches were applied to the lower body and the throwing shoulder because most of the force production during the pitching motion would occur earlier in the kinetic chain. The aim of the present study was to analyze the effects of acute static stretching on upper-body muscles, so the leg muscles were not stretched. Time constraints also limited the amount of stretching that could be performed. Because previous research has indicated that acute static stretching can impair performance of the lower-body muscles, future studies are needed to determine if acute static stretching of the lower body has a significant impact on baseball pitching performance. It should be noted, though, that Knudson et al. (16) found static stretching of the legs along with the upper body did not significantly affect tennis serve velocity or accuracy.

No previous research has measured the effects of acute static stretching of the upper body on baseball pitching performance. Although most studies have focused on muscles of the lower body, only one study (16) used an overhand throwing motion (a tennis serve) to measure performance after static stretching. A short duration of static stretching may be performed during a warm-up because this does not appear to significantly affect throwing performance. A rest period of at least 5 minutes may help eliminate any possible negative effects of acute static stretching. The results of the present study, which are supported by previous research (16,35), suggest that acute static stretching of the upper body does not significantly affect pitching performance of collegiate baseball players.

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Practical Applications

Six 30-second static stretches of the throwing shoulder performed after an active warm-up had no significant effects on baseball pitching velocity or accuracy. A relatively short duration of upper-body static stretching followed by a rest period of at least 5 minutes may be included in a warm-up before a throwing activity without fear of decreasing velocity or accuracy. This study also indicates that acute static stretching of the upper body does not improve velocity or accuracy. If warm-up time is limited, abstaining from static stretching should not be detrimental to pitching performance. An active warm-up that includes at least 10-15 minutes of throwing appears to be an adequate amount of preparation for a collegiate baseball pitcher.

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Acknowledgments

Thanks to coach Chris Schwarz and the UW-L baseball team for their cooperation and participation in this study and to Hannah Gaveske and Laura Capp for assisting with the stretching protocol. The results of the present study do not constitute endorsement of the JUGS cordless radar gun by the authors or the National Strength and Conditioning Association.

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Keywords:

velocity; accuracy; warm-up; overhand throw

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