Professional baseball pitchers with increased in-pitch stance hip flexion excursion demonstrate higher shoulder internal rotation torque and elbow varus torque with no appreciable ball speed benefit.

Abstract

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. It was hypothesized that pitchers with increased lead hip flexion would have increased shoulder external rotation and increased ball velocity. 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 analysis of variance between subgroups. Multiregression 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 > .05). PRO pitchers with high lead hip, high stance hip flexion (Q1) had significantly higher shoulder internal rotation torque (5.1 vs. 4.8% body weight by body height [BW×BH], P = .03) and elbow varus torque (5.0 vs. 4.7% BW×BH, P = .02) compared with pitchers with high lead hip, low stance hip flexion (Q3). Similarly, pitchers with low lead hip, high stance hip flexion (Q2) had significantly greater shoulder internal rotation torque (5.2 vs. 4.8, 4.9% BW×BH, P_max = .02) and elbow varus torque (5.1 vs. 4.7, 4.8% BW×BH, P_max = .03) compared with Q3 and pitchers with low lead hip, low stance hip flexion (Q4). When controlling for anthropometric parameters, the multiregression model noted stance hip flexion excursion was moderately predictive for elbow varus torque (P < .001, B = 0.010 [0.004, 0.016], β = 0.20) but weakly predictive for elbow medial force (P = .018, B = 0.064 [0.014, 0.115], β = 0.148), shoulder anterior force (P = .026, B = 0.066 [0.008, 0.123], β = 0.130), and shoulder internal rotation torque (P = .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 with 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 speed benefit noted. This may be an area of improvement in identifying and correcting maladaptive pitching patterns for players, pitching coaches, and athletic trainers.