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COMPARISON OF IN-GAME TRUNK AND UPPER EXTREMITY KINEMATICS BETWEEN PITCH TYPES IN COLLEGIATE BASEBALL PITCHERS

Abstract

BACKGROUND: Baseball pitchers commonly experience shoulder and elbow injuries. Pitch type has been identified as a possible risk factor, but previous biomechanical studies were limited to laboratory analysis. The purpose of this study was to compare in-game trunk and upper extremity kinematics between fastballs, breaking balls, and changeups in collegiate baseball pitchers. METHODS: Twenty-four NCAA Division I collegiate baseball pitchers (1.9±0.1m; 94.5±10.5kg) who threw at least five in-game fastballs, breaking balls, and changeups were included in this study. Trunk and throwing-arm kinematics were recorded during games using a markerless motion capture system (300Hz). A TrackMan V3 Game Tracking unit defined pitch type. Kinematics of each pitcher’s first five pitches of each pitch type were averaged for analysis. A repeated measures multivariate analysis of variance (MANOVA) was used to assess within-subject differences between each pitch type (α = .05). The variables of interest were shoulder abduction at foot contact (FC), shoulder horizontal abduction at FC, shoulder external rotation at FC, shoulder maximum external rotation (MER), elbow flexion at MER, maximum shoulder rotational velocity, lateral trunk tilt at ball release (BR), shoulder abduction at BR, and elbow flexion at BR. RESULTS: The MANOVA revealed differences in kinematics between pitch types (F18,78 = 3.49, p<.001). Follow-up univariate testing revealed significant differences across pitch types for MER (F2 = 3.77, p=.03) along with shoulder abduction (F2 = 6.27, p=.004), lateral trunk tilt (F2 = 11.63, p<.001), and elbow flexion (F2 = 5.06, p =.01), all at BR. Pairwise comparisons revealed that fastballs had greater MER than breaking balls (mean within-subjects difference: 1.5±2.6°, p=.03). At BR, changeups resulted in greater shoulder abduction than fastballs (1.2±2.0°, p=.03) and breaking balls (1.5±2.3°, p=.01). Changeups produced less lateral trunk tilt at BR than fastballs (-3.6±4.8°, p=.003) and breaking balls (-2.9±4.2°, p=.008) and greater elbow flexion at BR than breaking balls (1.2±1.7°, p=.006). All other variables were not significantly different (p >.10). CONCLUSION: Collegiate pitchers had in-game kinematic differences between pitch types, especially at BR. It is unknown if these differences alter injury risk, but they may impact performance by showing the batter which pitch type will be thrown.

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