Exploratory Velocity-Adjusted Upper-Extremity Loading Profiles in Fastball Pitching: A Secondary Analysis of...

Background: Fastballs delivered at comparable velocities may differ in upper-extremity loading, but cross-sectional profile differences do not establish within-pitcher biomechanical mechanisms. Objective: To construct an exploratory velocity-adjusted elbow-shoulder loading profile and descriptively compare non-definitional kinetic-chain characteristics associated with high-velocity low- and high-adjusted-load profiles. Methods: This cross-sectional secondary analysis included 411 fastballs from 100 pitchers in the OpenBiomechanics Project. Elbow varus and shoulder internal rotation moments were adjusted for pitch velocity, body mass, height, age, throwing side, and playing level; standardized residuals were averaged into a composite score. Sample tertiles defined high-velocity low-adjusted-load (HVLL) and high-velocity high-adjusted-load (HVHL) profiles, and pitcher-cluster-bootstrap and sensitivity analyses assessed robustness. Results: HVLL included 47 pitches from 17 pitchers, and HVHL included 37 pitches from 17 pitchers; only two pitchers contributed to both profiles, making the HVLL-versus-HVHL contrast almost entirely inter-individual. Pitch velocity was comparable (144.41 vs. 143.39 km/h; difference, 1.01 km/h; 95% CI, -0.97 to 2.88; p = 0.310). HVLL pitches showed smaller lead-knee extension change (6.61 degrees vs. 19.85 degrees; difference, -13.25 degrees; 95% CI, -20.37 to -5.58; FDR-adjusted p = 0.010) and lower lead-knee extension angular velocity at foot plant (30.67 vs. 232.77 degrees/s; difference, -202.10 degrees/s; 95% CI, -293.22 to -88.82; FDR-adjusted p = 0.010). These differences were attenuated when pitcher fixed effects were used to define loading residuals, further limiting within-pitcher interpretation. Conclusions: Because only two pitchers contributed to both profiles, the contrast was almost entirely inter-individual and describes between-pitcher performance-loading organization. It generates hypotheses but does not establish within-pitcher mechanisms, injury risk, or coaching targets.