Journal of Strength and Conditioning Research, 2004, 18(3), 441–446 q 2004 National Strength & Conditioning Association
THE RELATIONSHIP BETWEEN BALANCE AND PITCHING ERROR IN COLLEGE BASEBALL PITCHERS DARRIN W. MARSH,1 LEON A. RICHARD,2 L. ALEXIS WILLIAMS,3
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KELLY J. LYNCH4
Saco Bay Orthopaedic and Sports Physical Therapy, Kennebunk, Maine 04043; 2SmartCare Physical Therapy, Dixfield, Maine 04224; 3Day-Kimball Hospital, Putnam, Connecticut 06260; 4Maxwell, Knowland, and Kluger-ENT Associates, Portland, Maine 04103. 1
ABSTRACT. Marsh, D.W., L.A. Richard, L.A. Williams, and K.J. Lynch. The relationship between balance and pitching error in college baseball. J. Strength Cond. Res. 18(3):441–446. 2004.— The objective of the study was to examine the relationship between balance and pitching error in college baseball pitchers. Sixteen college baseball pitchers, 9 National Association of Intercollegiate Athletics (NAIA) and 7 National Collegiate Athletic Association (NCAA) Division III, participated in the study. Balance ability, expressed as average sway velocity (deg·s21), during dominant leg unilateral stance with eyes open and eyes closed was quantified for each subject utilizing the Balance Master System 7.04 (long force plate). Additionally, each subject underwent sensory organization testing on the SMART EquiTest System providing information regarding the effective use of the somatosensory, visual, and vestibular inputs. Pitching error was assessed with a high-speed video camera recorder during spring practice. A JUGS radar gun measured pitch velocity. The mean pitching error was 37.50 cm with a mean pitch velocity of 78 miles·h21 (35 m·s21). No significant correlation was demonstrated between unilateral stance eyes open and pitching error (r 5 20.24; p 5 0.36) or unilateral stance eyes closed and pitching error (r 5 20.29; p 5 0.27). A significant negative correlation was demonstrated between sensory organization test 5 and pitching error (r 5 20.50; p 5 0.05) and between sensory organization test 5/1 and pitching error (r 5 20.50; p 5 0.05). Additionally, unilateral stance eyes closed demonstrated a positive correlation with pitch velocity (r 5 0.52; p 5 0.04). The results reveal that low levels of vestibular input utilization may lead to high levels of pitching error in college baseball pitchers. KEY WORDS. vestibular system, baseball pitching, sensory organization
INTRODUCTION aseball pitching is a specialized version of throwing that requires the performer to be highly accurate. The pitching motion or delivery is divided into 5 phases: (a) wind-up (or balance), (b) early cocking, (c) late cocking, (d) acceleration, and (e) follow-through (14). The wind-up phase of the pitching delivery constitutes the largest percentage (80%) of the time required to pitch a baseball (10). This phase is characterized by the ‘‘balance point’’ position. This position occurs when the pitcher’s stride leg reaches the apex of the leg lift. Subsequently, many baseball coaches have recommended balance exercises to improve balance in the balance point position (1, 5, 12, 15, 20, 22). These exercises are often performed as part of a regular-season training program and are thought to enhance pitching mechanics as well as increase pitching accuracy (reduce pitching error) (1, 3, 5, 12, 13, 15, 20, 22). Whatever the athletic performance setting, balance appears to be an essential part of athletic movement. Bal-
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ance is the ability to control the center of gravity (COG) over the base of support in a given sensory environment (2). Three sensory systems provide input for balance: somatosensory, visual, and vestibular (Table 1). Somatosensory input is derived from the forces and motions exerted and received by the feet on the support surface (16). Visual input is derived from sway-dependent motions of the head relative to the surrounding environment, while vestibular input is derived from head motions related to active or passive body sway in reference to gravity (16). Balance requires accurate information from sensory system input as well as effective processing by the central nervous system (CNS) in order to produce appropriate motor responses (4). No evidence exists to support the claim that balance and pitching error are related. Therefore, the purpose of this study was to investigate the relationship between balance and pitching error in college baseball pitchers. Specifically, we examined the relationship between unilateral stance and pitching error, as well as the relationship between sensory system input and pitching error.
METHODS Experimental Approach to the Problem
The study was a nonexperimental descriptive correlation investigation involving pitchers from 2 college baseball teams. All measurements were taken during the preseason. Computerized force-plate technology was utilized to measure balance in a laboratory setting. Two measures of balance were of interest: (a) unilateral stance ability in the balance point position and (b) utilization of sensory system input (somatosensory, visual, and vestibular) during normal stance. This information was correlated with pitching error data obtained through video and computer analysis prior to balance testing. Subjects
Twenty male college baseball pitchers participated in the study. All individuals gave written consent prior to participation. Individuals were informed of the study during preseason meetings at their respective institutions. An Institutional Review Board approved the test protocol. All individuals were questioned regarding past medical history, including upper- and lower-extremity injuries. Individuals were excluded if they were currently injured or were undergoing rehabilitation for a previous injury. Also excluded were individuals who had undergone surgery on the upper or lower extremity in the past year. Three individuals were cut from their respective teams during the course of the study, and 1 was unable to complete the 441
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Table 1. Utilization of the senses for balance.* Sense
Reference
Conditions favoring use
Somatosensory Visual
Support surface Surrounding objects
Vestibular
Gravity and inertial space
Fixed support surface Fixed visible surrounds and irregular or moving support Irregular or moving support and moving surrounds or darkness
Conditions disrupting use Irregular or moving support Moving surrounds, darkness Unusual motion environments
* Reprinted with permission from Dr. Lewis Nashner.
study because of his participation in another sport. Therefore, 16 subjects were left to participate in the study. The subjects were an average of 20.1 years of age (range 5 18–22). Average height was 182.3 cm, and there were 3 left-handed and 13 right-handed pitchers. Nine subjects competed at the National Association of Intercollegiate Athletic (NAIA) level of competition and 7 subjects competed at the National Collegiate Athletic Association (NCAA) Division III level of competition. At the time of data collection, all subjects were participating in regular indoor preseason practice sessions with no limitations. Test Protocol
Pitchers from 2 college baseball teams participated in the study and were evaluated on separate weekends 1 week apart. Team 1 completed the accuracy portion of testing and approximately 16 hours later performed the balance assessment. Team 2 completed the same protocol a week later. Pitching accuracy was measured at each team’s indoor practice facility. Measurement equipment, including an L-shaped apparatus and digital high-speed video camera recorder (Sony DCR-TRV320, Sony Electronics Inc., Park Ridge, NJ), was set up according to each team’s regular practice format. Subjects performed their normal warm-up routine prior to the assessment of pitching accuracy. The warm-up included a period of stretching and approximately 20 minutes of graded throwing activity. On average, testing of pitching accuracy took 15 minutes for each pitcher. Balance testing was performed at a private location proximal to both schools. Prior to testing, subjects were measured for height and instructed in the balance assessment protocol. Subjects wore gym shorts or sweat pants and removed their shoes during the test. Balance assessment took approximately 25 minutes per pitcher. A licensed audiologist with certification in computerized platform testing procedure performed all tests. Measurement of Pitching Error
Pitching error was assessed using a digital high-speed video camera recorder and an L-shaped apparatus to determine the position of the ball in the x–y plane as the ball crossed home plate. The apparatus was made of plywood, wooden beams, and aluminum and put together in such a way as to allow it to be disassembled and moved from one location to another (Figure 1). The dimensions of the apparatus were 183 cm high and 145 cm at its base. A 1-m long calibration mark was made on the upright beam of the apparatus to provide a scale on the video images. The apparatus was placed immediately adjacent to home plate at a position corresponding to the batter box. A weighted string was hung from an aluminum rod so that the weight on the string approximated the center of the x–y plane, or (0,0) point, which corresponded to the
FIGURE 1. Position of L-shaped apparatus and catcher for assessment of pitching error.
middle of the strike zone. The catcher was instructed to place his mitt in the same spot for each pitch. This was accomplished by marking the back of the catcher’s mitt with a white dot to be placed immediately in front of the weight on the end of the string. Pitching accuracy or error was defined as the distance of the ball from the original position of the catcher’s mitt, the (0,0) point, as the ball crossed home plate. Each pitcher threw 20 fastball pitches at game-situation intensity from a regulation indoor pitching mound. Pitchers were instructed to throw at a bright orange fluorescent dot located at the center of the catcher’s mitt. The pitching rubber, which is that part of the pitching mound the pitcher must stay in contact with during the pitching delivery, was measured to be 18.4 m from home plate. A recently calibrated JUGS radar gun (JKP Sports, Tualatin, OR) was used to measure the speed of each pitch. All pitches were recorded on tape using a digital high-speed video camera recorder placed directly to the right of the pitching mound. The video was then downloaded to a computer for analysis. Each pitch was viewed frame by frame. The frame immediately before the ball entered the catcher’s mitt was chosen as the best representative of the end-point of the pitch, and, thus, the position of the ball as it arrived to the target. This frame was captured and opened in Adobe Photoshop (Adobe Photoshop 5.0 LE, Adobe System Inc.). Using the pixel location of the target dot and the approximated center of the ball, the distance between the 2 was calculated in pixels. These figures were then converted into centimeters by utilizing the calibration mark on the upright section of the Lshaped apparatus.
RELATIONSHIP BETWEEN BALANCE Balance Assessment Equipment
The Balance Master 7.04 (NeuroCom International, Inc., Clackamas, OR) long force plate was chosen to measure unilateral stance in the balance point position. The long force plate consists of two 23 3 152 cm force plates. Each force plate rests on 2 force transducers with sensitive axes oriented vertically. A cable carries information from the force plate to a computer. The computer calculates the center of pressure and the vertical displacement of the COG using force plate information. A COG sway-velocity score is produced with small scores reflecting little movement and large scores reflecting more movement (17). The SMART EquiTest System was chosen to measure the use of sensory system input. The SMART EquiTest System consists of a platform (two 23 3 46-cm force plates) and a 3-sided visual surround controlled by a computer. Two servomotors move the dual force plate and visual surround in response to commands from the computer. The manipulation of the visual surround or the dual force plate (or both) to exactly follow the subject’s sway is referred to as sway referencing (18). This manipulation delivers inaccurate visual and/or somatosensory information so that subjects must rely more on the alternate senses to maintain balance (18). Force transducers under the dual force plate measure the vertical and horizontal forces exerted by the subject’s feet. Five surfaceforce measurements are quantified and used to calculate COG sway angle and limits of stability (18). From this information, an ‘‘equilibrium score’’ is calculated. The equilibrium score is an expression of how well the subject’s sway remains within the expected angular limits of stability during each sensory organization test (SOT). The score is expressed between 0 and 100, with 100 indicating maximum stability and 0 indicating maximum sway or a step off the platform (17). Balance Assessment
Unilateral stance was measured in the balance point position on the Balance Master long force plate. Standing on the dominant leg and placing the nondominant hip and knee at 908 flexion with the hands in front of the chest achieved the balance point position. Leg dominance was determined through the analysis of each subject’s pitching motion. That is, the leg used as the pivot leg during the pitching delivery was declared the dominant leg. Each subject was instructed to look straight ahead and ‘‘stand as steady as possible.’’ Subjects were tested for 3 trials with eyes open and 3 trials with eyes closed in the balance point position for a total of 6 trials. The time of each trial was 10 seconds. The average COG swayvelocity score of the 3 trials for eyes open and eyes closed was calculated and served as the subject’s overall score. Subjects were then fitted with a safety harness and examined on the SOT portion of the SMART EquiTest System (NeuroCom International, Inc., Clackamas, OR). The SOT includes 6 sensory conditions that evaluate standing balance (Table 2). The SOT protocol examines the subject’s ability to utilize somatosensory, visual, and vestibular inputs as well as the subject’s ability to suppress inaccurate sensory information (18). All subjects completed the SOT protocol, which included a single trial each of SOT 1 and SOT 2 and 3 consecutive trials each of SOT 3–SOT 6. All trials lasted for 20 seconds. The average score for each condition was used for analysis.
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Table 2. Sensory organization test analysis.* Condition
Eyes
Visual surround
Support surface
1 2 3 4 5 6
Open Closed Open Open Closed Open
Fixed Fixed Sway-referenced Fixed Fixed Sway-referenced
Fixed Fixed Fixed Sway-referenced Sway-referenced Sway-referenced
* Reprinted with permission from Dr. Lewis Nashner.
Additionally, ratio pairing of conditions was performed to reveal possible sensory integration difficulty. The somatosensory ratio was calculated by comparing SOT 2 and SOT 1 (SOT 2/1). This determined the ability of the subject to use input from the somatosensory system to maintain balance. Comparing SOT 4 to SOT 1 (SOT 4/1) derived the visual ratio. This established the subject’s ability to use input from the visual system to maintain balance. Lastly, the vestibular ratio was computed by comparing SOT 5 to SOT 1 (SOT 5/1). This determined the subject’s ability to use vestibular input to maintain balance. During sensory organization testing, all subjects were instructed to ‘‘stand as steady as possible’’ on the platform with their feet apart and gaze directed forward. Previous research has shown a range of correlation coefficients for SOT 1–6. Ford-Smith et al. (8) reported poor to good (intraclass correlation coefficient [ICC] 5 0.26–0.68) test-retest reliability of SOT scores in noninstitutionalized elderly. Sensory organization test 5 and 6 had the best reliability (ICC 5 0.64–0.68). Statistical Analyses
Descriptive statistics (mean and standard deviation) and the Pearson product moment correlation coefficient were calculated to show the strength and direction of the relationship between pitching error and each balance measurement (unilateral stance eyes open, unilateral stance eyes closed, SOT 1–6, and ratio pairing conditions 2/1, 4/1, and 5/1). This was repeated for pitch velocity and each balance measurement. An alpha level of 0.05 was used to designate statistical significance for the correlation. The Statview software package (Abacus Concepts, Inc., Berkeley, CA) was used for data analysis.
RESULTS Table 3 shows the means and standard deviations of subject scores obtained for each variable measured. Correlation and variance values are given in Table 4. Pitching error demonstrated a significant negative correlation to SOT 5, with r 5 20.50, p 5 0.05 (Figure 2), and to SOT 5/1, with r 5 20.50, p 5 0.05 (Figure 3). Also, pitching velocity demonstrated a significant positive correlation with unilateral stance eyes closed with r 5 0.52, p 5 0.04 (Figure 4). On the other hand, pitching error demonstrated no relationship to unilateral stance eyes open, unilateral stance eyes closed, SOT 1—SOT 4, SOT 6, SOT 2/1, or SOT 4/1. Additionally, pitch velocity demonstrated no relationship with unilateral stance eyes open, SOT 1— SOT 6, SOT 2/1, SOT 4/1, or SOT 5/1.
DISCUSSION A review of the literature did not reveal any study that has examined the variables that determine pitching er-
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Table 3. Pitching error, pitch velocity, and balance test results (mean 6 SD).* Mean 6 SD
Test Pitching error (cm) Unilateral stance E/O (deg·s21) Unilateral stance E/C (deg·s21) SOT 1 SOT 2 SOT 3 SOT 4 SOT 5 SOT 6 SOT 2/1 SOT 4/1 SOT 5/1 Pitching velocity (m·s21)
37.50 0.81 1.97 94.94 91.94 92.85 91.52 70.94 71.49 95.62 95.81 74.31 35.08
6 6 6 6 6 6 6 6 6 6 6 6 6
22.10 0.19 0.43 1.98 2.84 1.87 1.84 8.01 12.14 4.06 1.94 9.11 2.49
* E/O 5 eyes open; E/C 5 eyes closed; SOT 5 sensory organization test. Table 4. Correlation (r) and variance (r2) values between pitching error and balance test results.† Pitching error‡ Tests Unilateral stance E/O (deg·s21) Unilateral stance E/C (deg·s21) SOT 1 SOT 2 SOT 3 SOT 4 SOT 5 SOT 6 SOT 2/1 SOT 4/1 SOT 5/1
r
Variance (r2)
20.24 20.29 0.16 0.05 0.25 0.26 20.50* 0.03 20.18 0.16 20.50*
0.06 0.08 0.03 0.00 0.06 0.07 0.25 0.00 0.03 0.03 0.25
FIGURE 2. Correlation (r) between sensory organization test 5 and pitching error.
† E/O 5 eyes open; E/C 5 eyes closed; SOT 5 sensory organization test. ‡ Total number of pitches/pitcher (n 5 20). * p , 0.05.
ror. It has been speculated by some that balance ability and pitching error are related. Based on these speculations, this study sought to investigate the relationship between pitching error and balance in college baseball pitchers. The study did reveal several significant findings. First, SOT 5 was negatively correlated with pitching error (r 5 20.50; p 5 0.05). Second, ratio pairing of SOT 5/1 was negatively correlated with pitching error (r 5 20.50; p 5 0.05). Lastly, unilateral stance eyes closed was positively correlated with pitching velocity (r 5 0.52; p 5 0.04). The SOT findings suggest that the lower the vestibular-input utilization, the greater the pitching error. The correlation was moderate according to the guidelines set by Domholdt (6). Sensory organization is the ability of the CNS to select, suppress, and combine appropriate inputs under changing environmental conditions. The SOT provides a means for evaluating sensory organization. During SOT 5, balance is maintained by vestibular input alone, because in this condition vision is eliminated and somatosensory input is made inaccurate by sway referencing the support surface. The increase in body sway (decreased equilibrium score) experienced by subjects on SOT 5 suggested that reduced vestibular-input utilization may
FIGURE 3. Correlation (r) between sensory organization test 5/1 and pitching error.
cause declines in dynamic balance. Therefore, it is possible that pitchers who exhibit greater pitching error do so because of reduced utilization of vestibular input. The vestibular system is comprised of 3 major components: a peripheral sensory apparatus consisting of the otoliths and semicircular canals in the inner ear, a central processing system located in the vestibular nuclear complex, and a motor output system that is mediated through the vestibulo-ocular reflex (VOR) and the vestibulospinal
RELATIONSHIP BETWEEN BALANCE
FIGURE 4. Correlation (r) between pitching velocity and unilateral stance with eyes closed.
reflex (VSR) (9). The vestibular system functions to monitor the position of the head in space and to coordinate head and body movement to keep the body in balance. An additional function is to stabilize gaze while the head is moving. Many factors can affect the utility of vestibular input during pitching delivery. However, because of the vestibular system’s role in regard to balance, head stability may be the most important factor. This is because uncontrolled head motion complicates the use of vestibular information by interfering with estimates of body motion and position (11). Also, increased head motion may impair the VOR, leading to blurred vision (11). During the pitching delivery, head stability is maximally challenged, due in large part to the rapid movement of the body while balancing on 1 extremity. For instance, humeral angular velocities of up to 7,5508·s21 have been recorded during the acceleration phase of pitching delivery in elite baseball pitchers (7). Therefore, individuals who are less effective at stabilizing their head during pitching delivery may experience imbalance leading to inaccuracy. The moderate relationship between balance (vestibular input utilization) and pitching error accounts for only a small amount of the shared variance between the 2 variables (r2 5 0.25). This means that 25% of the variation in this model may be accounted for by the relationship between vestibular input and pitching error; 75% of the variation present is not accounted for by the relationship of the 2 variables to each other. Therefore, additional variables appear to have a role in pitching error. Related research in sports that require aiming at targets may provide insight into these variables. Williams et al. (23) examined the effects of anxiety on accuracy in table tennis. Subjects’ accuracy in hitting concentric circle targets was measured, as well as subjects’ anxiety during performance. The results found that high levels of anxiety have a significant negative effect on accuracy in table tennis.
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Also, Vickers (21) examined gaze behavior (eye movements) in expert and nonexpert female college basketball players during free-throw shooting. The results indicated that experts (those who made . 75% of their free throws) fixate their gaze earlier and for a longer duration during the preshot phase of the free throw shot than nonexperts. Additionally, experts demonstrated absence of gaze fixation on the target during the shot phase of the free throw. Vickers concluded that accuracy in the free throw may depend on the ability to turn eye tracking on and off at select times. Perhaps the most surprising find in the study was the moderate positive correlation between unilateral stance eyes closed in the balance point position and pitch velocity. The finding suggests a relationship between increased body sway at the balance point position with eyes closed and increased pitch velocity. The authors expected a negative correlation between sway velocity and pitch velocity. The explanation for this finding is unknown. There are several limitations to the study. First, we examined baseball pitchers at only 1 level of competition. Baseball pitchers at other levels may test differently due to their degree of physical development or exposure to baseball pitching. Second, unilateral stance in the balance point position was measured for ten seconds for each trial, and a mean score calculated. Two subjects did not complete the last trial of the eyes closed unilateral stance portion of the test. Therefore, a mean score was calculated from the trials completed. Third, testing unilateral stance in the balance point position for ten seconds may not be relevant to baseball pitching. This is because of the brief period of unilateral stance time required during the wind-up phase of the pitching delivery. Fourth, the SOT is designed to test balance responses. Other factors not related to sensory organization may play a role in functional performance tasks, including predictive, cognitive, and motor processes (19).
PRACTICAL APPLICATIONS Based on the results of this study, we cannot recommend the indiscriminate practice of the balance-point position by college baseball pitchers to reduce pitching error. However, college baseball coaches and pitchers may consider sport-specific exercises that stimulate the vestibular system. In order to stimulate the vestibular system, visual and somatosensory inputs must be eliminated or diminished simultaneously. Somatosensory input can be diminished by standing on a soft (foam) or narrow (balance beam) surface, while visual input can be eliminated by simply closing one’s eyes or diminished by moving the head quickly from side to side. Practicing the pitching delivery on a foam surface with eyes closed would represent a sport-specific method of stimulating the vestibular system. Furthermore, additional research is needed in this area of sports performance in order to define the determinants of pitching error.
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Acknowledgments We would like to thank Sandra Curwin, PhD, PT, for her contribution to this research. Also, we thank Dr. William Maxwell for his assistance and use of the Balance Master System. Additionally, we thank Robert Moss, PhD, ATC, and Mike Fillayaw, PT, for their review of this document. Above all, we thank the coaches and players for their participation in this research.
Address correspondence marsh@adelphia.net.
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