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KINEMATIC PREDICTORS OF INGAME FASTBALL VELOCITY IN NCAA DIVISION I BASEBALL PITCHERS

Abstract

BACKGROUND: Pitch velocity is a key measure of fastball performance in baseball pitchers. The kinematics related to ball velocity are traditionally examined in laboratory settings with marker-based motion capture systems. However, limited research exists investigating their influence on in-game performance. The purpose of this study was to identify the kinematic predictors of in-game fastball velocity in collegiate baseball pitchers. METHODS: Kinematic data from 57 NCAA Division I pitchers (height: 1.89 ± 0.06m, mass: 93.1 ± 1.18kg) were collected at 300hz using an eight-camera markerless motion capture system (KinaTrax, Boca Raton, FL). Data were processed and filtered using propriety KinaTrax software. Kinematics were measured at foot contact (FC) (stride length, shoulder rotation, shoulder horizontal abduction, and shoulder abduction), maximum shoulder external rotation (MER) (shoulder rotation and elbow flexion), ball release (BR) (elbow flexion, shoulder abduction, trunk flexion, trunk lateral flexion, and lead knee flexion). Maximum knee extension velocity as well as trunk and pelvis rotation velocity were also included for analysis. Fastball velocity was recorded using a TrackMan (Scottsdale, AZ) V3 Game Tracking unit. The average of each subject’s first five fastballs thrown in a game was used for analysis. A backward multiple linear regression (α = .05) was used to identify the kinematic predictors of in-game fastball velocity. RESULTS: The average fastball velocity from the cohort was 40.9 ± 1.22m/s (91.4 ± 2.73mph). After the backward elimination (cutoff of p ≥ 0.05), three predictors explained 17.7% of the variance in fastball velocity (F(3,54)=3.81, R2 =.177, p=.014). As fastball velocity increases by 1 m/s (2.2 mph), max lead knee angle velocity increases by 0.003°/s (β=0.003, t=2.46, p=.017), max trunk rotational velocity increases by 0.005°/s (β=0.005, t=2.40, p=.020), or lead knee flexion at BR decreases by 0.027° (β=-0.027, t=-2.33, p=.024), while all other variables are held constant. CONCLUSION: The findings show greater stride knee extension at BR, maximum stride knee extension velocity, and maximum trunk rotational velocity are predictors of in-game fastball velocity. Investigating in-game data provided similar results to those of prior laboratory studies, while a higher pitch velocity, fewer significant variables, and lower coefficient of determination were noted.

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