The Influence of Elbow Flexion and Arm External Rotation on Peak Elbow Valgus Torque and Ball Velocity in Baseball Pitching

Introduction Elbow injury, especially Ulnar Collateral Ligament (UCL) tear, is very common in baseball pitching. This is often attributed to high valgus torques repetitively stressing the ligament. The goal of this study was to research the effect of Elbow Flexion (EF) and arm External Rotation (ER) angle on Peak Valgus Torque (PVT) as well as ball velocity, using a three-folded approach. Methods Motion data of 12 Dutch A and AAA team pitchers were collected (29 pitches in total). Firstly, the relationships between the variables and outcomes were statistically evaluated with Generalized Estimating Equations (GEE). Secondly, simplified movements and EF and ER variations were input to a two-segment model, which was based on the hypothesis that valgus torque is generated by inertial effects from external rotation deceleration and forearm forward acceleration. Lastly, for one pitch per player, ER and EF angles were varied in simulations. Results Statistical significance was only observed for higher EF as a predictor of increased PVT and higher ER as a predictor of decreased ball velocity. In the two-segment model, PVT increased for higher EF and decreased for higher ER. The simulations showed different effects between pitchers, however, most trends were similar to those of the two-segment model. Ball velocity was maintained or increased with higher EF, while the influence of ER on ball velocity differed between players. Conclusion The two-segment model led to a more in-depth insight in the many factors influencing PVT in pitching. The results of this study suggest that higher ER and lower EF could lead to lower PVT, without necessarily giving in on performance. However, the results showed differences between pitchers. As previous studies reported opposite trends regarding ER, we believe that this discussion should be re-opened. Our findings suggest that some pitchers are more prone to elbow injury than others and that pitchers might be able to lower injury-risk by adapting their pitching technique.