Investigating the Influence of Modifiable Physical Measures on the Elbow Varus Torque - Ball Velocity Relationship in Collegiate Baseball Pitchers

Background: The mechanism of ulnar collateral ligament (UCL) injury during pitching is excessive elbow varus torque (EVT). The EVT-ball velocity (T-V) relationship allows concurrent assessment of player performance and UCL injury risk. Modifiable physical capacities may underlie individual variation seen in the T-V relationship.

Purpose: To identify physical performance characteristics that impact the T-V relationship during pitching.

Study design: Descriptive laboratory study.

Methods: A total of 87 National Collegiate Athletic Association Division I pitchers participated. Pitching collection involved measurement of EVT and ball velocity during 5 maximal effort fastballs thrown to a catcher. Physical measures collected were the following: shoulder and hip passive range of motion (ROM) and strength, shoulder rate of torque development (RTD), grip strength, and lumbopelvic stability. Physical measures were entered into univariate linear mixed models with ball velocity as a covariate to predict EVT. Variable reduction for multivariate models involved selection of physical measures based on random forest-derived variable importance and univariate relationship significance, rendering a 27-variable pool. Multivariate linear mixed models predicting EVT, adjusting for physical measures and other physical characteristics, were then created using backward elimination.

Results: In univariate analysis, for every 1 m/s (2.2 mph) increase in ball velocity, the mean EVT increased by 1.51 Nċm (95% CI, 0.66-2.37 Nċm; P = .001). In univariate analysis, hip abduction strength symmetry and bilateral lumbopelvic stability significantly increased EVT, while dominant-shoulder ROM, scaption RTD symmetry, and hip ROM significantly decreased EVT. Variables that increased EVT while controlling for ball velocity in the final model include grip strength symmetry, lead-leg lumbopelvic stability, and bodyweight. Increased dominant-shoulder internal rotation (IR) strength, dominant-shoulder flexion ROM, and scaption strength asymmetry decreased EVT as ball velocity increased.

Conclusion: Several modifiable physical measures affected EVT in the univariate analysis. In our final model, when controlling for ball velocity, EVT increased with increased grip strength symmetry, lead-leg lumbopelvic stability, and bodyweight and decreased with increased dominant-shoulder IR strength, dominant-shoulder flexion ROM, and scaption strength asymmetry.

Clinical relevance: Defining the individual and multivariate effects of these physical capacities on EVT contextualizes their role in the T-V relationship and helps identify access points through which coaches and clinicians can optimize a pitcher's T-V relationship.