Comparison of Kinematic and Temporal Parameters Between Different Pitch Velocity Groups

Transcription

1 ORIGINAL RESEARCH JOURNAL OF APPLIED BIOMECHANICS, 2001, 17, by Human Kinetics Publishers, Inc. Comparison of Kinematic and Temporal Parameters Between Different Pitch Velocity Groups Tomoyuki Matsuo, Rafael F. Escamilla, Glenn S. Fleisig, Steven W. Barrentine, and James R. Andrews This study investigated differences in kinematic and temporal parameters between two velocity groups of baseball pitchers. Data were collected from 127 healthy college and professional baseball pitchers. Those who threw faster than 1 SD above the sample mean (>38.0 m/s) were assigned to the high velocity group (n = 29), and those who threw slower than 1 SD below the sample mean (<34.2 m/s) were assigned to the low velocity group (n = 23). Twelve kinematic parameters and 9 temporal parameters were measured and analyzed. The pattern of lead knee movement was also investigated. Maximum shoulder external rotation, forward trunk tilt at the instant of ball release, and lead knee extension angular velocity at the instant of ball release were significantly greater in the high velocity group. Maximum lead knee flexion angular velocity was significantly greater in the low velocity group. Seventy percent of the high velocity group showed knee extension during the approach to ball release, whereas the low velocity group showed a variety of knee movement patterns involving less knee extension and more knee flexion. The greater shoulder external rotation in the high velocity group produced an increased range of motion during the acceleration phase. Key Words: baseball, high velocity, low velocity, biomechanics Introduction To date, numerous studies on biomechanical aspects of baseball pitching have been reported (Barrentine, Matsuo, Escamilla, Fleisig, & Andrews, 1998; Dillman, Fleisig, & Andrews, 1993; Escamilla, Fleisig, Barrentine, Zheng, & Andrews, 1998; Feltner & Dapena, 1986; Feltner, 1989; Fleisig, Andrews, Dillman, & Escamilla, 1995; Fleisig, Escamilla, Andrews, Matsuo, Satterwhite, & Barrentine, 1996; Gowan, Jobe, Tibone, Petty, & Moynes, 1987; Jobe, Moynes, Tibone, & Perry, 1984; Sakurai, Ikegami, Okamamo, Yabe, & Toyoshima, 1993). These studies provide useful information con- T. Matsuo is with the Faculty of Health & Sports Sciences at Osaka University, 1-17 Machikaneyama, Toyonaka, Osaka, Japan. R.F. Escamilla is with the Michael W. Krzyzewski Human Performance Laboratory in the Division of Orthopaedic Surgery at Duke University Medical Center, P.O. Box 3435, Durham, NC G.S. Fleisig, S.W. Barrentine, and J.R. Andrews are with the American Sports Medicine Institute, th Street South, Birmingham, AL

2 2 Matsuo et al. cerning how body segments move, such as the magnitudes of forces or torques that are generated during pitching. Gowan et al. (1987) investigated electromyographic differences between professional pitchers and amateur pitchers, and found significant differences in muscle activity between these two groups. The amateur pitchers used the rotator cuff muscles to a greater extent than the professional pitchers. These muscles primarily help position the humeral head within the glenoid fossa throughout the delivery of the pitch. Although these electromyographic data are useful, there was no description about differences in pitching kinematics. Several comparative investigations have been reported focusing on other throwing activities. For example, several javelin studies (Bartlett, Muller, Lindinger, Brunner, & Morriss, 1996; Mero, Komi, Korjus, Navarro, & Gregor, 1994; Whiting, Gregor, & Halushka, 1991) have found that better performers had a longer stride, less flexion of the lead knee during the final plant phase, greater approach velocity, and longer horizontal distance between the throwing side hip and the javelin center of mass. Joris, van Muyen, van Ingen Schenau, and Kemper (1985) compared good handball throwers to poor handball throwers, and found that good throwers could exert higher force and higher power just before ball release. In baseball, throwing with maximum ball velocity is a critical factor for a pitcher s success. However, in baseball pitching, there are no known studies that have focused on a kinematic comparison between different velocity groups. Thus, comparative investigations are needed to promote further understanding of the mechanics of baseball pitching. Several throwing studies have shown that sequential movements from proximal to distal segments led to successful performance in overarm throwing (Atwater, 1979; Joris et al., 1985; Mero et al., 1994; Putnam, 1993; Whiting et al., 1991). Nevertheless, a limited number of studies have focused on temporal differences between different performance groups. All those studies focused on javelin throwing (Mero et al., 1994; Morris & Bartlett, 1996; Whiting et al., 1991) and found no significant temporal differences between different performance groups. It seems necessary to investigate whether these temporal results from javelin throwing also occur in baseball pitching. The purpose of this study was to investigate differences in kinematics and temporal parameters during baseball pitching between high and low velocity groups. It was hypothesized that kinematic parameters measured during the acceleration phase of the pitch (i.e., from maximum shoulder external rotation to the instant of ball release) will show significant differences with greater values for the high velocity group, and that temporal parameters will show significant differences between the two velocity groups. Identifying kinematic and temporal differences will help the pitcher and coach determine pitching mechanics that produce maximum ball velocity. Methods Data were collected from 127 healthy college and professional baseball pitchers tested at the American Sports Medicine Institute. The mean and standard deviation (SD) of pitch velocity and anthropometric measurements were determined for all 127 subjects (Table 1). Those subjects with a pitch velocity greater than 1 SD above the mean (>38.0 m/s) were assigned to the high velocity group, while those subjects with a pitch velocity greater than 1 SD below the mean (<34.2 m/s) were assigned to the low velocity group. Therefore, a total of 52 subjects were assigned to either the high velocity group (21 professional and 8 college) or the low velocity group (23 college). Comparisons of kinematic and temporal parameters were made between the high velocity group and the low velocity group.

3 Kinematic and Temporal Parameters 3 Table 1 Physical Characteristics and Ball Velocities High velocity Low velocity Total (n = 127) group (n = 29) group (n = 23) Variable M SD M SD M SD Body height (m)* Body mass (kg) Humerus length (m)* Radius length (m)* Ball velocity (m/s)* *Significant differences (p <.01) between high and low velocity groups. The testing procedures followed previously reported protocols (Fleisig et al., 1996; Escamilla et al., 1998). Each subject reported for testing on one of his regularly scheduled pitching days. After providing history information and informed consent, the subject changed into a pair of spandex shorts, and body weight, body height, humerus length, and radius length were measured. Reflective markers (3.81 cm diameter) were attached bilaterally at the lateral malleoli, lateral femoral epicondyles, greater trochanters, lateral superior tip of the acromions, and lateral humeral epicondyles. A reflective marker was also positioned on the ulnar styloid process of the non-pitching wrist, while a reflective band approximately 1 cm wide was placed around the pitching wrist. Once the markers were positioned on the body, the subject was given an unlimited amount of time for stretching, warm-up throwing, pitching off an ATEC (Athletic Training Equipment Company, Sparks, NV) indoor pitching mound, and any other type of preparation he desired. Subjects were instructed to prepare just as if they were going to pitch in a game. Each subject threw toward a strike zone ribbon located over home plate at a regulation distance of 18.4 m from the pitching rubber. Once a subject was ready to pitch as in a game environment, fastball data were collected. Ball velocity at the instant of ball release was measured by the Jugs radar gun (Jugs Pitching Machine Company, Tualatin, OR) from behind home plate. Each subject threw 5 8 fastball pitches, with approximately s rest between each pitch. The three trials with the highest ball velocities and thrown for strikes were analyzed and averaged for each subject. Kinematic and temporal differences among the three trials for each subject have been shown to be small and insignificant (Fleisig et al., 1996; Escamilla et al., 1998). A Motion Analysis (Motion Analysis Corporation, Santa Rosa, CA) three-dimensional automatic digitizing system was used to quantify each pitcher s motion. Four electronically synchronized charged couple device cameras transmitted pixel images of the reflective markers directly into a video processor, with each camera operating at 200 Hz. Three-dimensional marker locations were calculated with Motion Analysis Expertvision 3-D software (Motion Analysis Corporation, Santa Rosa, CA), utilizing the direct linear transformation method (Abdel-Aziz & Karara, 1971; Shapiro, 1978).

4 4 Matsuo et al. The camera coefficients were calibrated by recording the position of markers attached to four vertically-suspended wires. Three reflective markers, which were 0.61 m apart from each other, were attached to each wire. These wires were positioned so that the markers made a matrix approximately 1.5 m 1.2 m 1.2 m in size, and were suspended approximately 0.3 m above the ground. The 1.5 m dimension of the matrix was aligned with the direction of the pitch. This matrix was designed to encompass as much of the testing area as possible while having each marker visible in the field of view of all four cameras. The root mean-square error in the calculation of the three-dimensional marker location was found to be less than 1.0 cm. Kinematic parameters (Figures 1 and 2) and temporal parameters were calculated using the same methods previously described (Dillman et al., 1993; Fleisig et al., 1996; Escamilla et al., 1998). Lead foot contact was automatically determined as the time when the lead ankle velocity decreased to less than 1.5 m/s, while the instant of ball release was automatically quantified as the second video frame (0.01 s) after the wrist passed the elbow in the sagittal plane (i.e., the XgZg plane in Figure 2) direction (Fleisig, 1994; Escamilla et al., 1998). The position data were digitally filtered independently in the Xg Figure 1 Definition of upper arm angular parameters: (a) elbow flexion, (b) shoulder abduction, (c) shoulder horizontal adduction, and (d) shoulder external rotation.

5 Kinematic and Temporal Parameters 5 (from the center of the pitching rubber to the center of home plate; Figure 2a), Yg (the cross product of the Zg and Xg unit-vector), and Zg (pointing vertical) directions. A fourthorder zero-lag Butterworth digital low-pass filter was used with a cutoff frequency of 13.4 Hz (Winter, 1990). Nine linear and angular velocities were analyzed: (a) maximum pelvis Figure 2 Definition of parameters concerning trunk and lower extremities: (a) forward trunk tilt, (b) upper torso rotation angular velocity (Wu) and pelvis rotation angular velocity (Wp), (c) lead knee flexion, and (d) stride length.

6 6 Matsuo et al. linear velocity; (b) maximum pelvis rotation angular velocity; (c) maximum shoulder horizontal adduction angular velocity; (d) maximum lead knee flexion angular velocity; (e) maximum upper torso rotation angular velocity; (f) maximum forward trunk tilt angular velocity; (g) maximum elbow extension angular velocity; (h) maximum shoulder internal rotation angular velocity; and (i) knee extension angular velocity at the instant of ball release. Stride length was defined as the linear distance from the center of the pitching rubber to the lead ankle marker (Figure 2d). It has been suggested that a large shoulder external rotation induces stretch shortening cycles in shoulder muscles during baseball pitching (Feltner & Dapena, 1986; Feltner, 1989), during handball throwing (Joris, 1985), and during javelin throwing (Morris & Bartlett, 1996). This large shoulder external rotation is assumed to be an important factor in increasing ball or javelin velocity. Therefore, maximum shoulder external rotation was also quantified in the current study. Forward trunk tilt at the instant of ball release was also analyzed, since weight transfer and a longer arm path during the acceleration phase are believed to be critical factors in throwing skills. According to studies on javelin throwing, lead knee movement during the delivery for the good throwers is different from that for the poor throwers (Morris & Bartlett, 1996; Whiting, et al., 1991). Therefore, patterns of lead knee movement were also investigated. Putnum (1993) recommended that joint angular velocities or segment angular velocities should be used for investigating the sequential movements in throwing. Therefore, nine temporal parameters that are primarily related to angular velocities were calculated to investigate differences in temporal patterns of pitching between the high velocity group and the low velocity group. The nine temporal parameters were: (a) time of maximum pelvis linear velocity; (b) time of maximum pelvis rotation angular velocity; (c) time of maximum shoulder horizontal adduction angular velocity; (d) time of maximum lead knee flexion angular velocity; (e) time of maximum upper torso rotation angular velocity; (f) time of maximum shoulder external rotation; (g) time of maximum forward trunk angular velocity; (h) time of maximum elbow extension angular velocity; and (i) time of maximum shoulder internal rotation angular velocity. These temporal parameters were shown as relative values, where 0% corresponded to lead foot contact and 100% corresponded to the instant of ball release. Means and standard deviations of all the parameters were analyzed in each group. Student s t tests were conducted for comparison of techniques used by the two groups. In order to correct for type I errors, the significance level was set at p <.01. Results Body height, arm length, and ball velocity were significantly greater in the high velocity group compared to the low velocity group (Table 1). No significant differences were observed in body mass between these two groups. No significant differences were found in shoulder or elbow angular velocities between the high velocity group and the low velocity group (Table 2). Four of the 12 kinematic parameters were significantly different between the high velocity group and the low velocity group. Compared to the low velocity group, the high velocity group demonstrated significantly less maximum lead knee flexion angular velocity and significantly greater lead knee extension angular velocity at the instant of ball release. Maximum shoulder external rotation and forward trunk tilt at the instant of ball release were significantly greater in the high velocity group compared to the low velocity group.

7 Kinematic and Temporal Parameters 7 Table 2 Comparison of Kinematic Parameters Between High and Low Velocity Groups High velocity Low velocity group (n = 29) group (n = 23) Variable M SD M SD Stride length (% body height) Maximum pelvis linear velocity (m/s) Maximum pelvis rotation angular velocity (º/s) Maximum shoulder horizontal adduction angular velocity (º/s) Maximum lead knee flexion angular velocity (º/s)* Maximum upper torso rotation angular velocity (º/s) Maximum shoulder external rotation (º)* Maximum forward trunk tilt angular velocity (º/s) Maximum elbow extension angular velocity (º/s) Maximum shoulder internal rotation angular velocity (º/s) Lead knee extension angular velocity at the instant of ball release (º/s)* Forward trunk tilt at the instant of ball release (º)* *Significant differences (p <.01) between high and low velocity groups. Table 3 Comparison of Temporal Parameters Between High and Low Velocity Groups High velocity Low velocity group (n = 29) group (n = 23) Variable M SD M SD Maximum pelvis linear velocity Maximum pelvis rotation angular velocity Maximum shoulder horizontal adduction angular velocity Maximum lead knee flexion angular velocity Maximum upper torso rotation angular velocity Maximum shoulder external rotation Maximum elbow extension angular velocity* Maximum forward trunk tilt angular velocity Maximum shoulder internal rotation angular velocity* Note. Each number in the table represents relative percent values, where 0% corresponds to lead foot contact and 100% corresponds to the instant of ball release. Negative values occur before lead foot contact. *Significant differences (p <.01) between high and low velocity groups.

8 8 Matsuo et al. Only two temporal parameters showed significant differences between the high velocity group and the low velocity group (Table 3). Maximum shoulder internal rotation angular velocity occurred just after the instant of ball release, occurring slightly later in the low velocity group compared to the high velocity group. Maximum elbow extension angular velocity occurred just prior to the instant of ball release, occurring slightly later in the low velocity group compared to the high velocity group. No significant difference was Figure 3 Patterns of lead knee movement. The horizontal axis showed the time duration from lead foot contact (0%) to the instant of ball release (100%).

9 Kinematic and Temporal Parameters 9 found between the time durations from lead foot contact to the instant of ball release for the high velocity group and the low velocity group, which were ± s and ± s, respectively. Four common knee movement patterns (types A, B, C, and D) were observed during the relative time interval from lead foot contact to the instant of ball release (Figure 3). For the high velocity group, approximately 80% of subjects were classified into two major patterns, type A and type B. For the low velocity group, however, types A, B, C, and D were all common. The type A pattern showed small knee flexions and extensions between approximately knee angles from 0 60% of the relative time interval, and knee extension from approximately 55 to 30 knee angles between % of the relative time interval. The type A pattern was typical for the high velocity group (69%), but only occurred in 9% of the low velocity group. In contrast, the type B pattern showed progressive knee flexion from approximately knee angles between 0 60% of the relative time interval, and slight knee extension from approximately 50 to 45 knee angles between % of the relative time interval. The type B pattern was observed in 14% of the high velocity group and 26% of the low velocity group. The type C pattern oscillated between approximately knee angles throughout the duration of the relative time interval. The type C pattern occurred in 26% in the low velocity group, but only in 3% of the high velocity group. The type D pattern demonstrated continuous knee flexion from knee angles throughout the 0 100% time interval. The type D pattern occurred in 17% of the low velocity group but was not observed in the high velocity group. Discussion As hypothesized, kinematic and temporal differences were found between the high velocity group and the low velocity group. Moreover, as expected, three of the four kinematic parameters with significant differences were greater in the high velocity group compared to the low velocity group. Using collegiate pitchers, Escamilla et al. NRfu (1998) demonstrated that during the fastball pitch the knee begins extending just prior to maximum shoulder external rotation and continues extending throughout the remainder of the pitch. Concomitant with knee extension, the trunk rotates forward (Escamilla et al., 1998). This relationship between knee extension and forward trunk rotation is important in baseball pitching. During the arm acceleration phase, the high velocity group extended their knees at a greater rate and through a larger range compared to the low velocity group. Since the extending lead knee helps brace and stabilize the lead leg, this may enhance the ability of the trunk to more effectively rotate forward over the braced lead leg. Elliott et al. (1988) also reported that the ability to drive the body over a stabilized lead leg was characteristic of high ball velocity pitchers. Allowing the knee to flex as the instant of ball release is approached may hinder forward trunk rotation and cause the pitcher to throw with a more upright trunk. In javelin throwing, it was found that less flexion of the lead leg during the final double support phase led to a greater release velocity (Bartlett et al., 1996; Morriss & Bartlett, 1996; Whiting et al., 1991). Whiting et al. (1991) also found that better javelin throwers exhibited a clear double flexion-extension pattern, but poorer throwers did not. This double flexion-extension pattern was also observed in the high velocity group (Figure 3, type A). Whiting et al. (1991) suggested the role of the lead leg in javelin throwing was to brace the body, thus allowing the trunk and upper extremities to accelerate forward over a braced lead leg and aid in the transfer of momentum up through the trunk to the throwing arm. Although body movements prior to lead foot contact are completely differ-

10 10 Matsuo et al. ent between baseball pitching and javelin throwing, the role of the lead leg appears the same. The large momentum of the body prior to lead foot contact during baseball pitching is transferred to the lead leg after lead foot contact. A stabilizing leg through knee extension helps transfer energy through the trunk to the throwing arm and may be one of the critical factors for maximizing pitch velocity. The rectus femoris muscle may serve an important role in knee and hip movements during baseball pitching. Morris and Bartlett (1996) assumed that the rectus femoris muscle in the lead leg contracted during the final double support phase first eccentrically and then concentrically in the javelin throw. The same is probably true in baseball pitching. Since the rectus femoris muscle is a two-joint muscle, contraction of this muscle causes both knee extension and hip flexion. Therefore, the concentric activity assumed to be occurring in the rectus femoris as the lead knee extends may also contribute to the increased forward trunk tilt that was demonstrated by the high velocity group. This suggests that strengthening the knee extensor muscles may be important for the throwing athlete, since these muscles help brace the lead leg during pitching. Furthermore, fatigue in these muscles may increase knee flexion and decrease the bracing effect of the lead leg. Fatigue in the knee extensors may also inhibit forward trunk tilt, causing a pitcher to throw with a more upright trunk. Since a braced lead leg may help create angular momentum of the trunk about the trunk s mediolateral and longitudinal axes, we expected that the angular velocities related to trunk movement for the high velocity group would be greater than those for the low velocity group. However, the two groups did not differ in maximum pelvis rotation angular velocity, maximum upper torso rotation angular velocity, and maximum forward trunk tilt angular velocity. Nevertheless, the potential importance of those parameters in generating ball velocity should not be minimized. The high velocity group had significantly greater shoulder external rotation during the arm-cocking phase compared to the low velocity group. This implies that for the high velocity group, the throwing shoulder externally rotated through a greater range of motion during the arm cocking phase. As the shoulder externally rotates, the shoulder internal rotators contract eccentrically to control the rate of shoulder external rotation. Feltner and Dapena (1986) and Fleisig et al. (1996) reported that maximum shoulder internal rotation torque occurred just prior to maximum shoulder external rotation, and suggested that the shoulder internal rotators eccentrically contract during this time and store elastic energy. Moderate to high muscle activity from the shoulder internal rotators have been reported during the arm cocking phase ( DiGiovine et al., 1992; Gowan et al., 1987; Jobe et al., 1983; Jobe et al., 1984). Stored elastic energy, the myotatic reflex, and a greater rate of force production in these pre-stretched and eccentrically contracting muscles may generate more powerful concentric contractions from the shoulder internal rotators during the arm acceleration phase of the pitch. It has been demonstrated that moving through a greater range of motion through increased flexibility can enhance the efficacy of the stretch-shortening cycle (Wilson et al., 1992). Applying force and accelerating the ball over a greater distance enhances ball velocity. Neal et al. (1991) reported that highly skilled throwers were able to move the arm segments through a greater range of movement and into more extreme positions compared to lesser skilled throwers. Since for the high velocity group the ball begins the acceleration phase with a greater amount of shoulder external rotation and ends the acceleration phase with greater forward trunk tilt, the distance the ball traveled was greater in the high veloc-

11 Kinematic and Temporal Parameters 11 ity group compared to the low velocity group. Since the time duration during the acceleration phase was nearly identical for both velocity groups (0.026 ± s for the high velocity group and ± s for the low velocity group), the ball achieved a higher average velocity and acceleration for the high velocity group. It seems, therefore, the linkage of knee extension, trunk rotation, and shoulder external and internal rotations are major contributors to increasing ball velocity. The approximately 4 cm greater total arm length (i.e., humerus plus radius) and 5 cm greater body height in the high velocity group compared to the low velocity group may partially explain why the high velocity group had a 15% greater ball velocity compared to the low velocity group. This is because for a given joint or segment angular velocity, the distal end of a longer segment travels at a greater linear velocity than the distal end of a shorter segment. Although all angular velocities of the trunk and throwing arm for the high velocity group appeared greater (1 8%) compared to the low velocity group, these differences were not significant. Nevertheless, the apparent differences may be important. The additive effects of the slightly increased angular velocities and significantly greater arm length and body height for the high velocity group may result in increased tangential velocities starting with proximal segments (legs and trunk) and ending with distal segments (arms and hand). Consequently, an increase in ball velocity will ensue. During the acceleration phase, the elbow begins extending just prior to maximum shoulder external rotation, while the shoulder begins internally rotating just after maximum shoulder external rotation. The timing between peak angular velocities between elbow extension and shoulder internal rotation is important in optimizing the transfer of energy and momentum from the arm to the ball. Both maximum elbow extension angular velocity and maximum shoulder internal rotation angular velocity occurred earlier in the high velocity group compared to the low velocity group. Furthermore, maximum shoulder internal rotation angular velocity occurred closer to the instant of ball release in the high velocity group compared to the low velocity group. These data imply that the high velocity group may have more optimal timing in generating peak elbow extension and shoulder internal rotation angular velocities compared to the low velocity group. This may partially explain why the high velocity group generated greater ball velocity compared to the low velocity group. Interestingly, in the earlier portion of pitch, the standard deviations of the temporal parameters were diverse, whereas standard deviations in the later part of the pitch were very small (Table 3). This implies that regardless of skill level, leg and trunk movements were most different among subjects, while arm movements were most similar. For the pitchers who have acquired a certain level of throwing skill, the key to increasing ball velocity may be in modifying the earlier part of pitching motion, especially leg and trunk movements. References Abdel-Aziz, Y.I, & Karara, H.M. (1971). Direct linear transformation from comparator coordinates into object space in close-range photogrammetry. In ASP ASPUI symposium on close-range photogrammetry (pp. 1-19). Falls Church, VA: American Society of Photogrammetry. Atwater, A.E. (1979). Biomechanics of overarm throwing movements and of throwing injuries. Exercise and sport sciences reviews, 7,

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13 Kinematic and Temporal Parameters 13 Whiting, W.C., Gregor, R.J., & Halushka, M. (1991). Body segment and release parameter contributions to new-rules javelin throwing. International Journal of Sport Biomechanics, 7, Wilson, G.J., Elliott, B.C., and Wood, G.A. (1992). Stretch shorten cycle performance enhancement through flexibility training. Medicine and Science in Sports and Exercise, 24, Winter, D.A. (1990). Biomechanics and motor control of human movement. New York: Wiley Interscience. Acknowledgments The authors would like to thank Anthony Demonia and Phillip Sutton for their assistance in collecting and digitizing the data.