Evaluating Pelvis Rotation Style at Foot Contact: A Propensity Scored Biomechanical Analysis in High School and Professional Pitchers.

BACKGROUND

Early pelvis rotation has been associated with decreased throwing arm kinetics and conventionally was considered a component of proper pitching form in baseball throwers. However, previous assessments of pelvis rotation style have not accounted for confounders such as playing level, anthropometric characteristics, or ball velocity and have not evaluated sufficient sample sizes.

PURPOSE

To compare kinetic and kinematic parameters based on pelvis rotation style in high school and professional pitchers.

STUDY DESIGN

Descriptive laboratory study.

METHODS

High school and professional baseball pitchers threw 8 to 12 fastball pitches while being evaluated using 3-dimensional motion capture (480 Hz). These pitchers were 1:1 propensity score matched by age, height, weight, handedness, and ball velocity based on early (<60°) versus late (≥60°) pelvis rotation style at foot contact. A total of 26 kinematic and 10 kinetic parameters were compared between groups. The kinematic parameters were used to conduct a linear regression between early and late pelvis rotation at foot contact.

RESULTS

Pelvis rotation at foot contact was not significantly associated with ball velocity for either high school ( = .243) or professional pitchers ( = .075). No difference was found in elbow varus torque between high school early rotators (57.5 ± 14.9 N·m) and late rotators (51.3 ± 14.7 N·m; = .036) and between professional early rotators (80.1 ± 11.8 N·m) and late rotators (79.0 ± 11.2 N·m; = .663). At foot contact in high school pitchers, stride length increased by 2.1% of body height (B = -0.205; β = -0.470; < .001), trunk rotation increased by 4.2° (B = -0.417; β = -0.488; < .001), and trunk flexion at foot contact decreased by 4.4° (B = 0.442; β = 0.476; < .001) with every 10° increase in pelvis rotation. At foot contact in professional pitchers, stride length increased by 2.3% of body height (B = -0.229; β = -0.478; < .001), trunk rotation increased by 4.3° (B = -0.431; β = -0.515; < .001), and trunk flexion decreased by 4.0° (B = 0.404; β = 0.373; < .001) with every 10° increase in pelvis rotation.

CONCLUSION

Pelvis rotation at foot contact was associated with several kinematic parameters in both groups and may influence mechanics further along the kinetic chain. Landing open or closed was not significantly associated with throwing arm kinetics or ball velocity for both high school and professional baseball pitchers, contrary to previous thought.

CLINICAL RELEVANCE

Coaches and players may better focus their efforts on refining other kinematic parameters for enhanced performance outcomes and safe pitching mechanics.