The Influence Of Shoulder Kinematics On Throwing Velocity In Baseball Players

Baseball pitching involves substantial rotation and velocity within the glenohumeral joint, placing the shoulder at an elevated risk of injury. Better understanding of joint kinematics during throwing may assist in the development of effective training and injury prevention protocols. PURPOSE: To test the relationship between throwing velocity (TV) and shoulder mechanics in baseball players. METHODS: We evaluated 100 pitchers (7 high school, 75 college, 18 professional) using an OptiTrack Prime 17 W high-speed motion capture system. After a standardized warmup, subjects were analyzed on 5 consecutive pitches. Kinematic parameters were horizontal abduction angle (HAA), external rotation angle (ERA), and internal rotation velocity (IRV). Maximum values (max) and values at foot plant (fp) were recorded separately. TV was assessed using a Stalker Sport radar system. Linear regression measured the effect of all independent variables on TV holding confounders constant. RESULTS: Subject age was 21.4 ± 2.3 yr, height was 185.3 ± 7.2 cm, HAAmax was 48.0 ± 12.5°, HAAfp was 41.9 ± 13.2°, ERAmax was 168.9 ± 10.1°, ERAfp was 47.3 = 21.2°, IRVmax was 4,521.8 ± 300.1°/s, and TV was 84.8 ± 4.7 mph. Age (r = 0.331; p < 0.001), height (r = 0.250; p = 0.012), IRVmax (r = 0.331; p < 0.001), ERAmax (r = 0.359; p < 0.001), HAAmax (r = 0.384; p < 0.001), and HAAfp (r = 0.414; p < 0.001) were correlated with TV. HAAfp (r = -0.091; p = 0.368) and ERAfp (r = -0.035; p = 0.729) were unrelated. In the regression analysis, age and level of play were highly correlated (VIF > 2.5); age was retained owing to better significance. In the full model, HAAmax was insignificant (p = 0.787) and was removed. Holding age (p < 0.001) and height (p < 0.001) constant, significant predictors of TV were IRVmax (β = 0.005; p < 0.001; 95% CI: 0.003, 0.007), ERAmax (β = 0.088; p = 0.024; 95% CI = 0.012, 0.163), HAAfp (β = 0.126; p < 0.001; 95% CI = 0.063, 0.190), and ERAfp (β = 0.042; p = 0.028; 95% CI = 0.005, 0.079). The model was significant (r2 = 0.500; p < 0.001). HAAfp and ERAfp were only significant with confounders controlled; HAAmax was only significant without confounders controlled. CONCLUSIONS: The three most robust predictors of TV were HAAfp, ERAmax, and IRVmax. Consideration should be given to exercise and injury prevention programs that focus on these parameters.