Relationships between the stance leg's lumbopelvic control and throwing arm kinetics have been established in baseball pitchers; however, no study to date has analyzed the role hip flexion excursion may play in generation of throwing arm kinetics/ball velocity. To discern a plausible relationship between lead and stance hip flexion excursion with throwing arm kinetics, full body kinematics, and ball velocity in professional (PRO) baseball pitchers. PRO (n=283) pitchers instructed to throw 8-12 fastball pitches were evaluated with 3D-motion capture (480 Hz). PRO pitchers were divided into quartiles based on "high" and "low" lead and stance hip flexion excursion with ANOVA analysis between subgroups. Multi-regression models examined the association between lead and stance hip excursion, controlling for anthropometric parameters, with ball velocity and throwing arm kinetics. The quartile divisions noted no difference for ball speed between subgroups(p>0.05). PRO pitchers with Hi Lead Hip, Hi Stance Hip flexion (Q1) had significantly higher shoulder internal rotation torque (5.1 vs 4.8%BWxBH, p=0.03) and elbow varus torque (5.0 vs 4.7%BWxBH, p=0.02) compared to pitchers with Hi Lead Hip, Low Stance Hip flexion(Q3). Similarly, pitchers with Lo Lead Hip, Hi Stance Hip flexion (Q2) had significantly greater shoulder internal rotation torque (5.2 vs 4.8, 4.9%BWxBH, pmax=0.02) and elbow varus torque(5.1 vs 4.7, 4.8%BWxBH, pmax=0.03) compared to Q3 and pitchers with Lo Lead Hip, Lo Stance Hip flexion (Q4). When controlling for anthropometric parameters, the multi-regression model noted stance hip flexion excursion was moderately predictive for elbow varus torque (p<0.001, B=0.010 [0.004, 0.016], β=0.20), while weakly predictive for elbow medial force (p=0.018, B=0.064 [0.014, 0.115], β=0.148), shoulder anterior force (p=0.026, B=0.066 [0.008, 0.123], β=0.130), and shoulder internal rotation torque (p=0.002, B=0.009 [0.003, 0.015], β=0.180). PRO pitcher subgroups with high stance hip flexion (Q1, Q2) consistently demonstrated higher elbow varus torque and shoulder internal rotation torque compared to pitchers with low stance hip flexion(Q3, Q4); these results were corroborated with a moderate and weakly predictive regression analysis when controlling for confounders, respectively. This suggests professional pitchers with increased stance hip flexion may be at higher risk for increased throwing arm kinetics, as a surrogate for injury risk, with no appreciable ball velocity benefit noted. This may be an area of improvement in identifying & correcting maladaptive pitching patterns for players, pitching coaches, & athletic trainers.
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