The Effects Of Hip And Torso Kinematics On Fastball Velocity In Baseball Pitchers

Baseball pitching involves the transfer of energy through the kinetic chain, including the hips and torso. Understanding how fastball kinematics affect throwing velocity (TV) will help inform coaches and other sport personnel in devising optimal training programs. PURPOSE: To evaluate the relationship between TV and hip and torso kinematics in male baseball pitchers. METHODS: We assessed the hip and pelvis mechanics of 100 baseball pitchers (18 professional, 75 college, and 7 high school) with motion capture cameras (Optitrack Prime 17 W). Variables assessed were maximum torso rotational velocity (TRmax), maximum pelvis rotational velocity (PRmax), maximum hip-shoulder separation (HSSmax), and hip-shoulder separation at foot plant (HSSfp). TV was assessed using a Stalker Sport radar system. All pitchers underwent an identical warm-up followed by 5 evaluated pitches. Regression analyses measured the effect of each kinematic parameter on TV with confounders held constant. RESULTS: Subjects were 21.4 ± 2.3 years old, 185.3 ± 7.2 cm tall, and weighed 90.7 ± 10.1 kg. TRmax was 1050.0 ± 87.2°/s, PRmax was 745.8 ± 96.3°/s, HSSmax was 32.1 ± 6.7°, and HSSfp was 29.7 ± 6.8°. TV was 84.8 ± 4.7 mph, and differed across play levels (p = 0.002). TV was also related to age (r = 0.331; p < 0.001), height (r = 0.250; p = 0.012), and weight (r = 0.245; p = 0.014). TV was correlated with TRmax (r = 0.328, p < 0.001), HSSmax (r = 0.299, p = 0.002), and HSSfp (r = 0.304, p = 0.002); TV was not related to PRmax (r = 0.011, p = 0.910). HSSmax and HSSfp were correlated (r = 0.929; p < 0.001); when both were included in the regression model, variance inflation factors were 8.1 and 7.7 respectively; HSSfp was retained owing to its stronger correlation both alone and in the full model. PRmax was removed owing to insignificance in the full model (p = 0.265). Holding age, height, and TRmax constant, HSSfp did not reach significance (β = 0.108; p = 0.101); it was removed. In the final regression model, age (β = 0.598; p = 0.001; 95% CI: 0.239, 0.957), height (β = 19.633; p < 0.001; 95% CI: 8.325, 30.940), and TRmax (β = 0.018; p < 0.001; 95% CI: 0.009, 0.028) were significant predictors of TV (R2 = 0.283; p < 0.001). CONCLUSIONS: Maximum trunk rotation velocity was the only significant predictor of TV when tested together. Exercises that increase torso velocity may benefit pitchers.