Trail Leg Hip Power: Influence On Elbow Varus Torque In Baseball Pitchers

Abstract

Although excessive elbow varus torque has been reported to contribute to ulnar collateral ligament (UCL) injury in baseball pitchers, contributing factors remain relatively unknown. The lower extremities generate power that is transferred up through the kinetic chain in pitching. Specifically, the trailing hip generates triplanar power during the stride phase. Diminished trailing hip power generation during pitching may necessitate compensatory power generation at the trunk and shoulder, potentially impacting elbow torque. PURPOSE: To determine the relationship between hip power and elbow varus torque during pitching. METHODS: Participants (n = 48) were high-school and collegiate baseball pitchers (17.6 ± 2.5 yrs, 1.85 ± 0.06 m, 84.7 ± 13.4 kg). Reflective markers were placed on the bilateral lower extremities (femoral condyles, malleoli, calcaneus, and distal foot), spine, scapulae and both upper extremities (acromia, humeral epicondyles, styloids of the wrist, and hand). Kinematics and kinetics (instrumented mound) were obtained from the trail limb during 3 maximal effort fastball pitches (36.9 ± 2.5 m/s). Ball velocity (m/s) was measured using an automated ball tracking system. Stride phase was defined as the time between peak stride knee height and stride foot contact. Elbow varus torque and hip power were quantified using inverse dynamics equations and normalized to body weight. Hip power was calculated as the resultant sum of X, Y and Z components expressed in the hip joint coordinate system. Linear regression was used to evaluate the relationship between peak elbow varus torque and hip power, using ball velocity as a covariate. Significance was set to 0.05. RESULTS: Peak hip power was found to be negatively associated with peak elbow varus torque (B = -0.02, p = 0.003, R2 = 11.2%). CONCLUSION: Lower hip power production is associated with higher elbow varus torque during the stride phase of pitching. Greater use of the trail hip during the stride phase may allow pitchers to decrease elbow torque while maintaining ball velocity. Future work should explore intermediate relationships in the pitching kinetic chain to establish a mechanism by which increased hip power may mitigate elbow varus torque in pitching.