Abstract
Abstract
Efficient baseball pitching relies on coordinated trunk–arm coupling during the
acceleration phase. Shoulder elevation is commonly maintained near 90°, and
prior work has focused on discrete metrics rather than continuous regulation.
Our purpose was to examine whether the deviation of shoulder elevation from 90°
during the acceleration period was associated with ball velocity. Markerless
kinematic data were collected from 362 National Collegiate Athletic Association
pitchers (7,239 pitches). Shoulder elevation was defined as the relative angle
between the trunk and the upper arm, and root mean square deviation from the 90°
reference was calculated across the acceleration period. Two-level linear
mixed-effects models were used to evaluate within- and between-pitcher
associations. Shoulder elevation deviation demonstrated high between-pitcher
consistency (intraclass correlation coefficient=0.95). Reduced root mean square
deviation was associated with higher ball velocity at both the between-pitchers
(β=− 0.06 mph·deg–1, p = 0.006) and within-pitchers
(β=− 0.07 mph·deg–1, p = 0.004) levels. Allowing
pitcher-specific slopes significantly improved a model fit, indicating
heterogeneity in the magnitude of this association and suggesting that the
reduced deviation of shoulder elevation during acceleration is associated with
higher ball velocity. Continuous quantification of shoulder elevation during the
acceleration phase provides a complementary perspective to discrete joint angle
analyses and may serve as an indicator of pitching performance.