Kinematic comparisons of 1996 Olympic baseball pitchers

Transcription

1 Journal of Sports Sciences, 2001, 19, 665± 676 Kinematic comparisons of 1996 Olympic baseball pitchers RAFAEL F. ESCAMILLA, 1 * GLENN S. FLEISIG, 2 NIGEL ZHENG, 2 STEVEN W. BARRENTINE 2 and JAMES R. ANDREWS 2 1 Michael W. Krzyzewski Human Performance Laboratory, Duke University Medical Center, PO Box 3435, Durham, NC and 2 American Sports Medicine Institute, th Street South, Birmingham, AL 35205, USA Accepted 11 February 2001 The aim of this study was to compare and evaluate the kinematics of baseball pitchers who participated in the 1996 XXVI Centennial Olympic Games. Two synchronized video cameras operating at 120 Hz were used to video 48 pitchers from Australia, Japan, the Netherlands, Cuba, Italy, Korea, Nicaragua and the USA. All pitchers were analysed while throwing the fastball pitch. Twenty-one kinematic parameters were measured at lead foot contact, during the arm cocking and arm acceleration phases, and at the instant of ball release. These parameters included stride length, foot angle and foot placement; shoulder abduction, shoulder horizontal adduction and shoulder external rotation; knee and elbow exion; upper torso, shoulder internal rotation and elbow extension angular velocities; forward and lateral trunk tilt; and ball speed. A one-way analysis of variance (P < 0.01) was used to assess kinematic diþ erences. Shoulder horizontal adduction and shoulder external rotation at lead foot contact and ball speed at the instant of ball release were signi cantly diþ erent among countries. The greater shoulder horizontal abduction observed in Cuban pitchers at lead foot contact is thought to be an important factor in the generation of force throughout the arm cocking and arm acceleration phases, and may in part explain why Cuban pitchers generated the greatest ball release speed. We conclude that pitching kinematics are similar among baseball pitchers from diþ erent countries. Keywords: biomechanics, fastball, pitching, throwing. Introduction Baseball is a relatively new Olympic sport, having made its debut at the 1992 Barcelona Olympic Games. International baseball teams compete in regional competitions to determine which teams advance to the Olympic Games. Five regions have been identi ed by the International Olympic Committee for international baseball competition (Osinski, 1998): Africa, the Americas, Asia, Europe and Oceania. For the 1996 Olympics, all of these regions were represented except Africa. Pitching kinematics are instilled in a pitcher at a young age in junior league baseball and reinforced throughout the pitcher s baseball career (Thurston, 1998). Although an adult pitcher s morphology cannot be altered, muscular strength and pitching kinematics, * Author to whom all correspondence should be addressed. rescamil@duke.edu such as joint and segment angles, positions and velocities, can be altered to help improve performance. Although baseball pitching kinematics have been well documented (Barrentine et al., 1998; Escamilla et al., 1998), much of this research focused on American baseball pitchers. There are limited data to compare pitching mechanics between diþ erent countries and cultures. Some pitching kinematic parameters have been quanti ed for Japanese (Sakurai et al., 1993), Australian (Elliott et al., 1986) and Korean (Han et al., 1996) collegiate and professional pitchers. However, shoulder abduction, elbow angle and ball speed were the only kinematic parameters these studies had in common. In addition, all studies in the literature that involve biomechanical analyses of baseball pitching were performed in simulated conditions; no studies have analysed pitching biomechanics during competition. As it is likely that pitching mechanics may be slightly diþ erent in laboratory-simulated conditions than during a game, the results of the current study provide Journal of Sports Sciences ISSN print/issn X online Ó 2001 Taylor & Francis Ltd

2 666 Escamilla et al. a database for high-standard pitchers from several countries who were analysed during competition. Knowledge of diþ erences in pitching mechanics among players from diþ erent countries is valuable to coaches, trainers and biomechanists in learning strategies for selecting optimal kinematics for athletic performance. Many coaches believe that pitching mechanics are taught diþ erently in diþ erent countries (Osinski, 1998; Thurston, 1998), which may result in diþ erences in pitching kinematics. Several kinematic parameters, such as knee exion, shoulder external rotation, elbow exion and shoulder abduction, have been reported as being diþ erent between Korean professional pitchers and American professional pitchers (Han et al., 1996). We hypothesized that kinematic diþ erences, which may be due to diverse coaching and training methodologies or to diþ erent anthropometric characteristics (e.g. body heights and arm lengths), would be found among baseball pitchers from various countries and cultures. The aim of this study was to compare preferred pitching kinematics among elite baseball pitchers from the eight countries that participated in the 1996 XXVI Centennial Olympic Games. Methods Fulton County Stadium in Atlanta, Georgia was the baseball venue for the 1996 XXVI Centennial Olympic Games. The eight countries that participated in the Olympic baseball competition were Australia, Japan, Korea, Italy, Cuba, the Netherlands, Nicaragua and the USA. Since professional baseball pitchers were not allowed to participate in the Olympics, all participants were considered amateurs. As all eight countries except Cuba have professional baseball leagues and professional pitchers who pitch in those leagues, the pitchers studied do not represent the best pitchers from their respective countries. Sixteen Olympic baseball games were videotaped over a 6-day period, with each country playing at least three games. Two synchronized high-speed video cameras (Peak Performance Technologies, Inc., Englewood, CO) collected data at a rate of 120 Hz. For each camera, the shutter speed was set at s and the aperture was adjusted according to weather conditions. Each camera was positioned approximately 50 m from the pitching mound with views from behind home plate and third base. Views from each camera were adjusted to capture the entire pitching motion while optimizing the eld of view. Video data were collected from 48 of the 59 pitchers listed on the rosters of the eight countries participating in the baseball competition. Of these 48 pitchers, 35 were right-handed and 13 were left-handed. Body mass, height, age and arm length were measured (Table 1); however, body mass was not available for pitchers from Italy, Korea, Nicaragua and the USA. Ball speed was recorded using a Jugs Tribar Sport radar gun (Jugs Pitching Machine Company, Tualatin, OR) as the ball left the pitcher s hand. Pitch type (i.e. fastball, curveball, change-up, slider, etc.) was determined through a combination of video analysis and from ball speed. Ball speed is highest during the fastball pitch, which is typically 3± 5 m s -1 faster than the slider and 5± 7 m s -1 faster than the curveball and change-up (Escamilla et al., 1998). Only the fastball pitch was analysed in this study. Each pitch thrown was recorded as either a ball or strike. A m three-dimensional calibration frame (Peak Performance Technologies, Inc., Englewood, CO), surveyed with a measurement tolerance of m, was recorded before and after the participants were videotaped. The calibration frame was positioned on the baseball mound in the same volume occupied by the baseball pitcher during the portion of the pitch from lead foot contact to the instant of ball release. It comprised 24 spherical balls of known spatial coordinates, with the x- and z-axes positioned parallel to the ground and the y-axis pointing vertically. The x-axis of the frame was 2 m long and pointed from the pitching rubber to home plate. The z-axis was the vector crossproduct of the x-axis and y-axis. Since kinematic parameters were measured only from lead foot contact to the instant of ball release, and not during the windup, stride, arm deceleration and follow-through phases, the m volume was large enough to contain the portion of pitching motion from lead foot contact to the instant of ball release. Table 1. Physical characteristics of the pitchers (mean ± s) Australia Italy Netherlands Japan Korea USA (n = 5) Cuba (n = 5) Nicaragua (n = 4) Body mass (kg) Height (m) Age (years) Arm length (m) 84 ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± 0.02

3 Kinematic comparisons of Olympic baseball pitchers 667 To minimize the eþ ects of fatigue, all pitching trials that were chosen for analysis were selected from the rst three innings a pitcher threw. For each pitcher, the three fastballs that were thrown for strikes and recorded the highest ball release speeds were chosen for kinematic analysis. A three-dimensional video system (Peak Performance Technologies, Inc., Englewood, CO) was used to manually digitize the data from each camera view for all 48 participants. A 14-point spatial model was created, consisting of the centres of the left and right mid-toes (third metatarsophalangeal joints), ankles, knees, hips, shoulders, elbows and wrists. Each of these 14 points was digitized in every video eld (120 Hz). Since these points were digitized through clothing and not from external markers, it was important to perform reliability and validity tests to determine digitizing accuracy and the validity of the results. To test for digitizing reliability, a single digitizer was able to digitize three separate trials so that segment lengths variations were 0.01± 0.02 m diþ erent for the three trials. Three diþ erent digitizers were then used to digitize the three trials for each participant (each trial being digitized by a diþ erent digitizer), with variations in segment lengths (e.g. thigh, leg, upper arm and forearm segments) also 0.01± 0.02 m diþ erent for the three trials. For example, the humerus segment (elbow to shoulder) was approximately 0.30 m long and the thigh segment was approximately 0.50 m long. A difference of 0.01± 0.02 m between or within digitizers would yield a digitized length diþ erence of 2± 6%. To test the validity of the kinematic measurements, the results of the current study will be compared with similar kinematic results from the literature in which external markers were and were not used during baseball pitching. Using the direct linear transformation method (Wood and Marshall, 1986), three-dimensional coordinate data were derived from the two-dimensional digitized images from each camera view. An average root mean square calibration error of m was produced. The data were ltered with a Butterworth low-pass lter with a cut-oþ frequency of 13.4 Hz (Fleisig et al., 1996; Escamilla et al., 1998). A computer program was written to calculate kinematic parameters. The ve-point central diþ erence method was used to calculate maximum upper torso angular velocity and maximum shoulder internal rotation angular velocity. The pitching motion was divided into several phases as previously de ned (Fleisig et al., 1996; Escamilla et al., 1998). Using methods previously described (Feltner, 1989; Fleisig et al., 1996; Escamilla et al., 1998), 21 kinematic parameters were calculated at lead foot contact (when the lead foot initially contacted the pitching mound), during arm cocking (from lead foot contact to maximum shoulder external rotation), during arm acceleration (from maximum shoulder external rotation to the instant of ball release) and at the instant of ball release. Angle conventions are shown in Fig. 1. At lead foot contact, eight kinematic parameters were measured on the pitching arm and lead leg. First, stride length was de ned as the linear distance from the stance ankle to the lead ankle. Secondly, foot placement was de ned as the mediolateral displacement between the lead ankle and stance ankle. For a right-handed pitcher, an open (positive) foot placement occurred when his lead ankle was to the left of his stance ankle, and a closed (negative) foot placement occurred when his lead ankle was to the right of his stance ankle. Thirdly, foot angle was de ned as the angle between the longitudinal axis of the foot and a vector pointing from the centre of the pitching rubber to the centre of home plate. For a right-handed pitcher, an open (positive) foot angle occurred when the lead foot pointed to the left of the straight-ahead position, and a closed (negative) foot angle occurred when the lead foot pointed to the right of the straight-ahead position. The other ve parameters were elbow exion angle (Fig. 1A), shoulder external rotation (Fig. 1B), shoulder abduction (Fig. 1C), shoulder horizontal adduction (Fig. 1D) and knee exion angle (Fig. 1E). Four kinematic parameters were measured during the arm cocking phase: maximum upper torso angular velocity (Fig. 1H), maximum elbow exion, maximum shoulder horizontal adduction and maximum shoulder external rotation. Three kinematic parameters were measured during the arm acceleration phase: maximum elbow extension angular velocity, maximum shoulder internal rotation angular velocity and average shoulder abduction during the arm acceleration phase. At the instant of ball release, six kinematic parameters were measured: knee exion angle, forward trunk tilt (the trunk angle to the vertical in the x-y plane; Fig. 1F), lateral trunk tilt (the trunk angle to the vertical in the y-z plane; Fig. 1G), elbow exion angle, shoulder horizontal adduction and ball speed. Five temporal variables were chosen for analysis as previously described (Fleisig et al., 1996, 1999): time to maximum upper torso angular velocity, time to maximum elbow exion, time to maximum shoulder external rotation, time to maximum angular velocity of elbow extension and time to maximum angular velocity of shoulder internal rotation. The temporal variables represent the timing of these ve kinematic measurements during the arm cocking and arm acceleration phases of the pitch. Each temporal value represented a percentage of the pitch completed, measured from lead foot contact to the kinematic parameter given, where 0% corresponds to lead foot contact and 100% corresponds to the instant of ball release.

4 668 Escamilla et al. Fig. 1. De nition of kinematic parameters, calculated in three-dimensional space: (A) elbow exion; (B) shoulder external/ internal rotation; (C) shoulder abduction; (D) shoulder horizontal abduction (negative)/shoulder horizontal adduction (positive); (E) lead knee exion; (F) forward trunk tilt; (G) lateral trunk tilt; (H) upper torso angular velocity (v UT ). Reprinted with permission from Escamilla et al. (1998). The kinematic data for the three trials for each pitcher were averaged. A one-way analysis of variance was used to assess kinematic and temporal diþ erences (P < 0.01) among pitchers from diþ erent countries, while Tukey s Honestly Signi cant Diþ erence post-hoc test (modi ed to compare any two groups with unequal group sizes) was used to assess pairwise comparison diþ erences (P < 0.01). The pitchers were then grouped into four geographical regions (the Americas, Europe, Asia and Oceania) and the diþ erences were re-analysed. An alpha level per comparison of 0.01 was chosen to reduce the Type I error rate for the set of comparisons while not dramatically in ating the Type II error rate. Results and discussion Only three of the 21 kinematic parameters quanti ed were signi cantly diþ erent among pitchers from the eight countries (Table 2). When pitchers from these eight countries were combined into four geographical regions, only two of the 21 kinematic parameters quanti ed were signi cantly diþ erent (Table 3). Since over 80% of the kinematic parameters were not signi - cantly diþ erent among pitchers from the eight countries and among pitchers from the four geographical regions, pitching kinematics appear to be similar among Olympic baseball pitchers from diþ erent countries and geographical regions. However, the small sample of pitchers from each country (each team only had 6± 8 pitchers on their roster) may have limited the statistical power required to detect signi cant diþ erences. Kinematic comparisons between the current study and the pitching literature are shown in Tables 4 and 5. There were no signi cant diþ erences in temporal measurements between countries (Table 6). The temporal values in the current study were similar to those reported previously for these same kinematic parameters (Fleisig et al., 1996, 1999). Fleisig et al. (1999) previously reported no signi cant diþ erences among youth, high school, college and professional pitchers for the same temporal measurements as in the

5 Table 2. Kinematic comparisons of 1996 Olympic baseball pitchers by country (mean ± s) Parameter Australia Italy Netherlands Japan Korea USA (n = 5) Cuba (n = 5) Nicaragua (n = 4) P-value Lead foot contact Stride length (m) Stride length (%ht) Foot placement (m) Foot angle ( ) Shoulder abduction ( ) Shoulder horizontal adduction ( ) Shoulder external rotation ( ) Knee exion ( ) Elbow exion ( ) 1.51 ± ± ± ± ± 8-25 ± ± 25** b 64 ± 6 92 ± ± ± ± ± ± 6-22 ± 8** a 39 ± ± 4 94 ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± 13** a 26 ± 20** 63 ± ± ± ± ± ± 8 89 ± 6-23 ± 9** a 30 ± ± ± ± ± ± ± ± 6-20 ± 5** a 47 ± ± 5 96 ± ± ± ± ± 6 93 ± 8-45 ± 11** 48 ± 9 67 ± 8 74 ± ± ± ± ± ± ± ± 14** b 58 ± 8 78 ± * 0.007* Arm cocking phase Maximum upper torso angular velocity (rad s -1 ) Maximum elbow exion ( ) Maximum shoulder horizontal adduction ( ) Maximum shoulder external rotation ( ) 23.0 ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± 8 21 ± ± ± ± ± ± ± ± ± ± Arm acceleration phase Maximum shoulder internal rotation angular velocity (rad s -1 ) Maximum elbow extension angular velocity (rad s -1 ) Average shoulder abduction ( ) ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± Instant of ball release Knee exion ( ) Elbow exion ( ) Forward trunk tilt ( ) Lateral trunk tilt ( ) Shoulder horizontal adduction ( ) Ball speed (m s -1 ) 67 ± 7 17 ± 4 37 ± 6 30 ± 10 8 ± 6 36 ± 2** c 62 ± 5 21 ± 8 31 ± ± 6 10 ± 5 36 ± 1** c 67 ± 6 22 ± 5 32 ± ± 12 6 ± ± 2** c 66 ± 9 23 ± 7 33 ± ± 23 6 ± ± 1 65 ± 7 17 ± ± ± ± 8 37 ± 1 60 ± 8 14 ± 5 45 ± ± ± ± 1** 67 ± 8 26 ± 4 29 ± ± ± ± 1** 66 ± 4 22 ± 4 28 ± 6 15 ± 1 12 ± ± 2** c < 0.001* * Signi cant diþ erence (P < 0.01) among countries. ** Signi cant diþ erence (P < 0.01) of post-hoc (Tukey s Honestly Signi cant Diþ erence) pairwise comparisons. a Signi cantly diþ erent than Cuba. b Signi cantly diþ erent than Japan. c Signi cantly diþ erent than Cuba and USA.

6 670 Escamilla et al. Table 3. Kinematic comparisons of 1996 Olympic baseball pitchers by geographical region (mean ± s) Parameter Oceania Europe (n = 14) Asia (n = 12) The Americas (n = 14) P-value Lead foot contact Stride length (m) Stride length (%ht) Foot placement (m) Foot angle ( ) Shoulder abduction ( ) Shoulder horizontal adduction ( ) Shoulder external rotation ( ) Knee exion ( ) Elbow exion ( ) 1.51 ± ± ± ± ± 8-25 ± ± 25** 64 ± 6 92 ± ± ± ± ± ± ± ± 22** a 65 ± 6 78 ± ± ± ± ± ± 8-20 ± ± 21** a,b 64 ± 8 74 ± ± ± ± ± ± 8-30 ± ± 17** 63 ± 7 97 ± * Arm cocking phase Maximum upper torso angular velocity (rad s -1 ) Maximum elbow exion ( ) Maximum shoulder horizontal adduction ( ) Maximum shoulder external rotation ( ) 23.0 ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± Arm acceleration phase Maximum shoulder internal rotation angular velocity (rad s -1 ) Maximum elbow extension angular velocity (rad s -1 ) Average shoulder abduction ( ) ± ± ± ± ± ± ± ± ± ± ± ± Instant of ball release Knee exion ( ) Elbow exion ( ) Forward trunk tilt ( ) Lateral trunk tilt ( ) Shoulder horizontal adduction ( ) Ball speed (m s -1 ) 67 ± 7 17 ± 4 37 ± 6 30 ± 10 8 ± 6 36 ± 2** b 64 ± 6 21 ± 7 31 ± ± 9 10 ± 6 36 ± 1** b,c 66 ± 7 20 ± ± ± 17 9 ± ± 1** 64 ± 8 21 ± 6 34 ± ± ± ± 2** < 0.001* * Signi cant diþ erence (P < 0.01) among countries. ** Signi cant diþ erence (P < 0.01) of post-hoc (Tukey s Honestly Signi cant Diþ erence) pairwise comparisons. a Signi cantly diþ erent than Oceania. b Signi cantly diþ erent than the Americas. c Signi cantly diþ erent than Asia. Note: Oceania represents Australia; Europe represents Italy and the Netherlands; Asia represents Japan and Korea; The Americas represents Cuba, Nicaragua and USA. current study. It can be inferred from these temporal data that the timing of when these maximum kinematic parameters occur is similar for pitchers of various standards and from diþ erent countries. Cuban and American pitchers exhibited signi - cantly greater ball release speed than pitchers from the Netherlands, Nicaragua, Australia and Italy. At lead foot contact, Cuban pitchers demonstrated signi cantly greater horizontal shoulder abduction than pitchers from Japan, USA, Italy and Korea, while Japanese pitchers showed signi cantly less shoulder external rotation than Australian and Nicaraguan pitchers. The mean shoulder horizontal adduction angle of -45 (i.e. 45 shoulder horizontal abduction) for the Cuban pitchers at lead foot contact is considerably greater than previously reported (-17 to -20 ) for collegiate pitchers throwing the fastball (Feltner, 1989; Sakurai et al., 1993; Fleisig et al., 1996; Escamilla et al., 1998). The greater shoulder horizontal abduction exhibited by Cuban pitchers may pre-stretch their anterior shoulder musculature (e.g. pectoralis major, anterior deltoids) more than pitchers from Japan, USA, Italy and Korea. This may position the throwing arm in a more eþ ective position to generate force throughout the remainder of the pitch, which may partially explain why Cuban pitchers generated the greatest ball release speed. However, this can only be a partial explanation, since the American pitchers attained equal throwing speeds with signi cantly less horizontal abduction than Cuban pitchers. In addition, although they had

7 Kinematic comparisons of Olympic baseball pitchers 671 similar ranges of horizontal abduction to Cuban pitchers, the Australian, Nicaraguan and Dutch pitchers had signi cantly slower throwing speeds. Nevertheless, increased horizontal abduction may help prevent the arm from moving towards the target prematurely during the arm cocking phase of the pitch. Neal et al. (1991) reported that less skilled throwers move their throwing arm towards the target prematurely, thereby losing the eþ ect of pre-stretching the involved muscles enjoyed by highly skilled throwers. The anterior shoulder muscles function primarily as shoulder horizontal adductors and internal rotators during the baseball pitch and have shown moderate activity during the baseball delivery (Jobe et al., 1983, 1984; Gowan et al., 1987). Pre-stretching these muscles during the early phases of the pitch may store elastic energy in these tissues, which may be used during the latter phases of the pitch. The storage and utilization of elastic energy during the stretch± shortening cycle have been well documented (Komi and Bosco, 1978; Bosco et al., 1982, 1987) and may enhance both passive and active muscle force production in baseball pitching. The importance of the stretch± shortening cycle has been demonstrated during the javelin throw (Bartlett and Best, 1988; Best et al., 1993; Mero et al., 1994), which has some similarities to baseball pitching. Other plausible factors that have been demonstrated to enhance concentric muscle contractile force subsequent to a pre-stretched or eccentrically contracting muscle are the myotatic (stretch) re ex and an increase in the rate of force production (Dietz et al., 1979; Bosco et al., 1982). Another potential advantage of greater shoulder horizontal abduction at lead foot contact is that it causes the throwing arm to move behind the trunk at this time. This may cause the trunk to rotate towards the throwing arm, thus placing the trunk musculature on stretch. The stored elastic energy from the pre-stretched rectus abdominis, external and internal obliques and paraspinal musculature (e.g. erector spinae, semispinalis, multi di, rotatores), together with the stretch± shortening cycle that occurs in these muscles during the arm cocking phase, may aid these muscles in generating trunk rotation. During the arm cocking phase, moderate to high activity from the rectus abdominis, abdominal obliques and lumbar paraspinal musculature has been reported in professional baseball pitchers (Watkins et al., 1989). Nevertheless, some baseball coaches do not advocate extreme shoulder horizontal abduction at lead foot contact based on the belief that excessive stress to the throwing shoulder may occur (Thurston, 1998). However, this belief has not been scienti cally validated. Furthermore, it is diý cult to know the optimal shoulder horizontal abduction that is needed at lead foot contact to maximize the storage and utilization of elastic energy throughout the remainder of the pitch. Shoulder external rotation at lead foot contact has been shown to vary widely in the literature (Table 4), ranging from 45 to 106, and to be usually associated with large standard deviations. The value for Japanese pitchers (262 ) in the current study is unusually low, implying that they were slow in externally rotating their throwing shoulder. This may cause the arm to lag behind the body during the subsequent arm cocking and arm acceleration phases of the pitch, which may increase elbow or shoulder joint forces. Kinetic analyses are needed to test this hypothesis. However, in contrast to the results of the current study, a shoulder external rotation at lead foot contact of 106 ± 22 (Fig. 1B, Table 4) has previously been reported for six Japanese university pitchers (Sakurai et al., 1993). Diþ erences in how lead foot contact was de ned by ourselves and Sakurai et al. (1993) may in part be responsible for these discrepancies in shoulder external rotation at lead foot contact. The greater ball release speed of American and Cuban pitchers is supported by data from the 1999 World, European and Pan-Am 18-Under tournaments (Clark, 2000), in which pitchers from Cuba (n = 9) and the USA (n = 9) had an average ball release speed of about 38 m s -1. In contrast, pitchers from Asia (Japan and Korea, n = 11), Europe (Italy and Netherlands, n = 17) and Australia all had mean ball release speeds of about 36 m s -1. Nevertheless, it is diý cult to infer from the current study why Cuban and American pitchers had signi cantly greater ball release speeds than pitchers from Australia, Italy, the Netherlands and Nicaragua. Body height and arm length are likely to in uence ball release speed. Although the Cuban and American pitchers were the tallest and had the longest arms in the current study, these diþ erences were not signi cant. With a larger sample size of pitchers from each country, more kinematic and anthropometric diþ erences may have been found. Most of the kinematic parameters that were quanti- ed in the current study had values similar to fastball data from many other studies involving high school, college and professional pitchers (Tables 4 and 5). A unique contribution of the current study is that it provides pitching kinematic data during competition among a diverse sample of elite pitchers from diþ erent countries. All other pitching studies in the literature involved pitchers in an arti cial pitching environment. As in the current study, some researchers have manually digitized joint centres through the baseball uniform without the use of external markers (Pappas et al., 1985a,b; Vaughn, 1985; Feltner and Dapena, 1986), while others aý xed external markers to the trunk and extremities during simulated pitching in laboratory environments (Elliott et al., 1986; Dillman et al., 1993; Werner et al., 1993; Fleisig et al., 1996,

8 Table 4. Linear and angular displacement comparisons among studies involving the fastball pitch (mean ± s) Reference Pitchers Standard Event Stride length (m) Shoulder abduction ( ) Shoulder horizontal adduction ( ) Current study 48 males Olympic Lead foot contact 1.51 ± ± 9-26 ± ± ± 10 Escamilla et al. (1998) 16 males College Lead foot contact 1.51 ± ± ± ± 7 10 ± 9 Sakurai et al. (1993) 6 males College Lead foot contact 83 ± ± 7 79 ± ± 8 11 ± 12 6 ± 7 Feltner and Depena (1986) 8 males College Lead foot contact 76 ± 9 92 ± 6-18 ± 8 2 ± 9 Fleisig et al. (1999) 115 males College Lead foot contact 1.56 ± ± 8 9 ± 9 Fleisig et al. (1999) 60 males Pro Lead foot contact 1.61 ± ± 9 9 ± 10 Shoulder external rotation ( ) 45 ± ± ± ± ± ± ± ± ± ± ± ± ± ± 11 Elbow exion ( ) 96 ± ± ± 7 84 ± ± ± ± ± ± ± ± 8 20 ± 6 85 ± ± ± 6 87 ± ± ± 5 Knee exion ( ) Forward trunk tilt ( ) Lateral trunk tilt ( ) 64 ± 7 65 ± 7 34 ± ± ± ± ± 5 28 ± 9 48 ± ± ± ± 8 38 ± ± 9

9 Han et al. (1996) 16 males Pro Lead foot contact 1.37 ± ± ± ± ± ± ± ± 14 Pappas et al. (1985b) 15 males Pro Lead foot contact ± ± Elliott et al. (1986) 6 males Pro Lead foot contact 1.54 ± ± 3 Dillman et al. (1993) 29 males College/pro Lead foot contact 1.41 ± ± ± 9 93 ± 8-30 ± ± 6 0 ± 5 53 ± ± ± 8 Werner et al. (1993) 7 males College/pro Lead foot contact Fleisig et al. (1996) 26 males College/HS Lead foot contact 1.36 ± ± ± ± 8 7 ± 7 67 ± ± ± ± ± 6 Vaughn (1985) 12 males College/HS Lead foot contact 19 ± 3 Abbreviations: HS = high school; Pro = professional. 57 ± ± ± ± ± ± ± ± 9

10 674 Escamilla et al. Table 5. Linear and angular velocity comparisons among studies involving the fastball pitch (mean ± s) Reference Pitchers Standard Maximum upper torso angular velocity (rad s -1 ) Maximum elbow extension angular velocity (rad s -1 ) Maximum shoulder internal rotation angular velocity (rad s -1 ) Ball speed at the instant of release (m s -1 ) Current Escamilla et al. (1998) Feltner and Dapena (1986) Fleisig et al. (1999) Fleisig et al. (1999) Han et al. (1996) Pappas et al. (1985b) Elliott et al. (1986) Dillman et al. (1993) Werner et al. (1993) Fleisig et al. (1996) Vaughn (1985) 48 males 16 males 8 males 115 males 60 males 16 males 15 males 6 males 29 males 7 males 26 males 12 males Olympic College College College Pro Pro Pro Pro College/pro College/pro College/HS College/HS 24.8 ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± 2 35 ± ± 2 37 ± 2 38 ± ± 3 36 ± 2 Abbreviations: HS = high school; Pro = professional. Table 6. Temporal comparisons of 1996 Olympic baseball pitchers by country (mean ± s) Parameter Australia Italy Netherlands Japan Korea USA (n = 5) Cuba (n = 5) Nicaragua (n = 4) Maximum upper torso angular velocity (% of pitch) Maximum elbow exion (% of pitch) Maximum shoulder external rotation (% of pitch) Maximum elbow extension angular velocity (% of pitch) Maximum shoulder internal rotation angular velocity (% of pitch) 44 ± ± ± 4 85 ± 5 96 ± 6 46 ± ± ± 9 84 ± 6 99 ± 6 52 ± ± ± 6 87 ± ± ± ± ± ± ± ± ± ± 4 86 ± ± ± ± ± 6 87 ± ± ± ± ± 7 89 ± ± 4 45 ± ± ± ± ± 4 Note: Each temporal value represents a percentage of the pitch completed (measured from lead foot contact to the kinematic parameter given), where 0% corresponds to lead foot contact and 100% corresponds to the instant of ball release. No signi cant diþ erences (P < 0.01) were found among countries. 1999; Escamilla et al., 1998). These methodological diþ erences among studies probably contributed to the large range of kinematic values speci ed above. For example, mean maximum angular velocity of shoulder internal rotation among the eight countries in the current study was 107 ± 10 rad s -1, which was quite similar to the 107 ± 30 rad s -1 reported by Feltner and Dapena (1986), the 108 rad s -1 reported by Pappas et al. (1985b) and the 107 ± 15 rad s -1 reported by Vaughn (1985), who also manually digitized joint centres through the baseball uniform without the use of external markers. In contrast, considerably larger mean maximum angular velocities of shoulder internal rotation have been reported by Escamilla et al. (1998; 132 ± 19 rad s -1 ), Fleisig et al. (1999; 130 ± 22 rad s -1 ), Dillman et al. (1993; 121 ± 19 rad s -1 ) and Fleisig et al. (1996; 132 ± 24 rad s -1 ), all of whom used external markers aý xed to the trunk and extremities during simulated pitching in the laboratory. The main diý culty with manual digitization during a game is that it involves estimating joint centres through the baseball uniform, which was a limitation to the current study. However, the many similar kinematic values between the current study and the pitching literature (Tables 4 and 5) helps validate the kinematic values reported here. Conclusions Twenty-one pitching kinematic variables were measured and compared among pitchers representing eight countries that participated in the 1996 XXVI

11 Kinematic comparisons of Olympic baseball pitchers 675 Centennial Olympic Games. Since only three kinematic parameters were signi cantly diþ erent among the pitchers, we conclude that pitching kinematics are similar among Olympic baseball pitchers from diþ erent countries. Nevertheless, the few kinematic diþ erences that were observed between countries may in uence pitching performance. Furthermore, diþ erent kinematics may also aþ ect risk of injury, since shoulder and elbow joint forces may change as pitching kinematics changes. Additional studies should be conducted to examine shoulder and elbow kinetics among pitchers from diþ erent countries, as well as to assess training and coaching methods among diþ erent countries. Acknowledgements We would like to acknowledge the IOC Subcommission on Biomechanics and Physiology of Sport for selecting this project for the 1996 XXVI Centennial Olympic Games. 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