Abstract
Baseball pitching places substantial mechanical demand on the shoulder and elbow, contributing to a high incidence of upper-extremity injury across competitive levels. Trunk kinematics are known to influence joint moments on distal structures, however it remains unclear how kinematics at different pitch phases influences these moments. PURPOSE: To examine how trunk and pelvis kinematics at different stages of pitching influence peak elbow varus and shoulder internal rotation (IR) moments while controlling for pitch speed and anthropometrics. METHODS: Open access markered motion capture (45 markers, 360 Hz) and ground reaction force (1080 Hz) data were collected from collegiate baseball pitchers (n=100 players, 411 total pitches; age=21.3±2.2 years). Three-dimensional kinematics and kinetics were calculated using inverse dynamics. All data was collected and variables calculated by the OpenBiomechanics Project (Wasserberger et al. 2022). Hip-shoulder separation and trunk orientation (anterior tilt, lateral tilt, and rotation) were quantified at foot plant (FP), maximum external rotation (MER), and ball release (BR). Trunk orientation changes were calculated from FP to MER and from MER to BR. Covariate-adjusted linear mixed-effects models were used to assess associations between trunk and pelvis kinematic changes at different stages and peak shoulder and elbow moments. Pitch velocity, age, height, and body mass were considered covariates, and subject identity was considered a random effect. RESULTS: Greater maximum hip–shoulder separation was positively associated with both peak elbow varus and shoulder internal rotation moments (β=0.777 and 0.847, respectively; p<0.05). Greater hip–shoulder separation at foot plant was negatively associated with peak elbow varus and shoulder IR moments (β=-0.760 and -0.898, respectively; p<0.05), suggesting earlier trunk–pelvis separation may reduce elbow and shoulder loading. Increased trunk lateral tilt toward the throwing arm during the acceleration phase (MER to BR) was also negatively associated with peak elbow varus moment (β=-0.488, p=0.048) ) but was not significantly related to shoulder internal rotation moment (β=-0.353, p=0.121). No other kinematic variables demonstrated significant relationships after controlling for covariates. CONCLUSION: Trunk and pelvis kinematics meaningfully influence upper-extremity joint loading during pitching regardless of pitch velocity. Greater maximum hip-shoulder separation increases net joint moments, while greater early hip-shoulder separation decreases them. This indicates that earlier rotation instead of simply enhancing maximal rotation optimizes kinetic chain force transfer, reducing the need for shoulder and elbow-driven force generation. Additionally, increased lateral trunk tilt toward the throwing side during acceleration may reduce elbow joint demand by decreasing the moment arm at the elbow. These findings support previous research highlighting the importance of trunk mechanics and timing for pitchers and suggest potential targets for technique instruction to minimize joint loading while maintaining performance.
Recommended Citation
Chockalingam, Kannaa R.; Doyle, Benjamin P.; and Mann, J Bryan
(2026)
"Timing-Dependent Trunk Kinematics are Associated with Reduced Shoulder and Elbow Joint Demands During Baseball Pitching,"
International Journal of Exercise Science: Conference Proceedings: Vol. 2:
Iss.
18, Article 138.
Available at:
https://digitalcommons.wku.edu/ijesab/vol2/iss18/138