Author(s): CHEN, S., CHANG, H., Institution: NATIONAL TAIWAN SPORT UNIVERSITY, Country: TAIWAN, Abstract-ID: 2790

INTRODUCTION:
Proximal to distal sequencing of body segments, typically characterized by shoulder–hip separation, is a fundamental biomechanical determinant of baseball pitching performance. While previous studies have primarily emphasized the magnitude of segmental separation, the temporal coordination between segments remains underexplored. Therefore, this study aimed to investigate the relationships among timing differences of body segments and pitching performance, specifically ball velocity and strike outcome, by using a wearable inertial measurement unit (IMU) system.
METHODS:
Twelve male collegiate baseball pitchers (age: 19.3±1.3 years, height: 181.0±7.1cm, weight: 85.5±13.3kg) participated in this study. Five IMUs were attached on the throwing arm, sternum, sacrum, axial-leg thigh, and lead leg. Each pitcher performed ten fastball pitches from an indoor turf mound. Pitch outcome (strike or ball) was determined by a catcher, resulting in 60 strikes and 32 balls. Ball velocity was measured using a radar gun positioned behind the pitcher. Only pitches reaching at least 80% of each pitcher’s maximal velocity were included. Timing differences between body segments—including throwing arm–thorax, throwing arm–pelvis, and thorax–pelvis—were calculated using the IMU system (Movella DOT) and exported for offline analysis. Spearman’s rank correlations and Wilcoxon signed-rank tests were employed for statistical analysis.
RESULTS:
Timing differences between the throwing arm–pelvis (p = .008) and between the thorax–pelvis (p = .041) were significantly greater in strikes than in balls, whereas no difference was found for the throwing arm–thorax timing (p = .666). Spearman’s rank correlations revealed a moderate negative association between throwing arm–pelvis timing difference and ball velocity (ρ = −0.516, p < .001), indicating that greater temporal separation was associated with reduced ball velocity. No significant correlations were found between ball velocity and either throwing arm–thorax or thorax–pelvis timing difference (p > .05).
CONCLUSION:
These findings suggest that temporal coordination of the throwing arm and pelvis plays a critical role in regulating the speed-accuracy trade-off during baseball pitching. Although increased temporal separation may facilitate improved segmental control and strike accuracy, it may simultaneously reduce the efficiency of the kinetic chain required for maximal ball velocity. Coaches and practitioners should consider that optimizing shoulder-hip separation timing may require distinct strategies depending on whether the tactical emphasis is velocity or precision.