Kinematic Parameters Associated With Elbow Varus Torque in Elite Adult Baseball Pitchers

Background: Numerous studies have investigated pitching kinematics associated with elbow varus torque, but these studies were limited in the parameters analyzed and/or the number of pitchers tested.Purpose/Hypothesis: The purpose of this work was to evaluate numerous kinematic parameters in a large sample of elite adult pitchers. It was hypothesized that several kinematic parameters would be associated with variations in elbow varus torque.Study Design: Descriptive laboratory study.Methods: A deidentified biomechanical database of 523 pitchers (425 professional; 98 collegiate) was analyzed. For each pitcher, 21 kinematic parameters and normalized elbow varus torque (% body weight x height) were calculated. A stepwise multivariate linear regression model evaluated significant findings. In addition, biomechanical differences were identified between the high- and low-torque groups using Mann-Whitney U tests.Results: Forty percent of the variance in normalized torque was explained by 11 kinematic parameters. Comparison of the high- and low-torque groups demonstrated significant differences in 10 of these parameters (all except pelvic angular velocity). Compared with the low-torque group, the high-torque group had greater ball velocity, shoulder abduction at foot contact, elbow flexion at foot contact, maximum knee extension velocity during arm acceleration, maximum elbow extension velocity during arm acceleration, and trunk contralateral tilt at ball release. In addition, the high-torque group had lower upper trunk tilt at foot contact, shoulder external rotation at foot contact, maximum external rotation, and shoulder abduction at ball release.Conclusion: Normalized elbow varus torque was associated with ball velocity and 10 other kinematic parameters. Ball velocity and 9 of these kinematic parameters were significantly different between the high-torque and low-torque groups. These parameters may be related to increased pitch velocity but also increased load within the throwing elbow.Clinical Relevance: This study provides pitchers, coaches, and trainers with objectives for modification of pitching mechanics to reduce elbow torque and possible risk of injury, particularly kinematics in the early phase of the pitching motion.