Releasing the Spring: The Association Between Trunk-on-Pelvis Acceleration and Ball Velocity in Baseball Pitching

The objective of this study was to compare the spring-like properties of pelvis and trunk rotation during baseball pitching in high school pitchers with varying ball velocities. It was hypothesized that high-velocity pitchers would be more effective at accelerating the trunk on the pelvis from foot contact to ball release. Three-dimensional kinematics were recorded in 35 high school pitchers (age 16.5 ± 1.1 year, height 1.83 ± 0.06 m, body mass 82.8 ± 9.9 kg, and pitch velocity 75.0 ± 5.6 mph). Pelvis and trunk angular velocities and accelerations, and trunk-pelvis separation, were calculated and averaged for 3 pitches. Additionally, average trunk-on-pelvis acceleration was calculated from foot contact to ball release. Pitchers were classified as high-, average-, or low-velocity, and single-factor ANOVA was used to compare metrics between groups. Peak pelvis and trunk velocities were higher for high- versus low-velocity pitchers (p = 0.001 and p = 0.008, respectively). Pelvis deceleration was greater in high-velocity pitchers (p = 0.024), and average trunk-on-pelvis acceleration was greater for high-velocity pitchers (p = 0.013). Acceleration of the trunk on the pelvis during the baseball pitch quantifies the spring-like properties derived from pelvis and trunk kinematic sequencing. High-velocity pitchers more effectively release the spring by decelerating the pelvis prior to ball release.