The Influence of Excessive Ipsilateral Trunk Tilt on Upper Extremity Throwing Mechanics: A Newly Characterized Parameter For Biomechanical Evaluation in High School and Professional Pitchers

Document Type

Journal Article

Publication Date

3-8-2022

Journal

Journal of shoulder and elbow surgery

DOI

10.1016/j.jse.2022.01.153

Keywords

Lateral trunk tilt; baseball; contralateral tilt; kinetics; motion-capture; throwing arm

Abstract

BACKGROUND: Though contralateral trunk tilt has been recognized, the phenomenon of excessive ipsilateral trunk tilt, often observed during earlier portions of the pitch, has not been explored as a potential correlate with throwing arm kinetics among baseball pitchers. The purpose of this study was to evaluate kinetic and kinematic parameters among high school and professional pitchers related to excessive ipsilateral/contralateral trunk tilt. METHODS: Professional and high school pitchers were assessed with 3D-motion capture (480 Hz) while pitching. Pitchers were grouped into an excessive ipsilateral tilt at foot contact (FC), neutral, or excessive contralateral tilt at ball release (BR). Trunk and shoulder kinematics as well as throwing arm kinetics were compared between subgroups with post-hoc regression analysis. RESULTS: Professional pitchers(n=287) had significantly higher ipsilateral trunk tilt at FC(p<0.001) compared to high schoolers(n=59). High school pitchers with excessive contralateral trunk tilt at BR experienced significantly higher shoulder superior force(27.0±7.4 vs. 17.6±5.1 %Body Weight[BW] respectively, p<0.001) and shoulder anterior force(39.6±8.2 vs. 35.7±5.4 %BW respectively, p<0.001) compared to the ipsilateral trunk tilt cohort, while had comparable ball velocity(30.2±3.2 vs. 30.4±2.1m/s, p=0.633). For professionals, for every 10° increase in ipsilateral trunk tilt at FC, ball velocity increased by 0.2m/s(B:0.02 β:0.07 SE: 0.005 p=0.010), while elbow varus torque(EVT) decreased by 0.1 %BWxHeight(B:-0.01 β:-0.08 SE:0.002 p<0.001) and shoulder internal rotation torque(SIRT) decreased by 0.1 %BWxHeight(B:-0.01 β:-0.07 SE:0.002 p=0.005). CONCLUSION: High school and professional pitchers with excessive ipsilateral trunk tilt at FC consistently demonstrated significantly decreased throwing arm kinetics (High school: shoulder anterior force, shoulder superior force; Professional: SIRT, EVT) compared to pitchers with excessive contralateral trunk tilt at BR, with equivalent ball velocity. In addition, professional pitchers appear to engage in significantly greater ipsilateral trunk tilt at early portions of the pitch when compared to high schoolers, which may represent a kinetically favorable method adopted by pitchers at higher playing levels to maintain adequate ball velocity while concomitantly minimizing throwing arm kinetics.

Department

School of Medicine and Health Sciences Student Works

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