Hip Adduction during Running: Influence of Sex, Hip Abductor Strength and Activation, and Pelvis and Femur Morphology.

PURPOSE To examine the influence of hip abductor strength, neuromuscular activation, and pelvis & femur morphology in contributing to sex differences in hip adduction during running. In addition, we sought to determine the best predictors of hip adduction during running for both males and females. METHODS Fifteen female and 14 male runners underwent strength testing, instrumented overground running (e.g., kinematics and muscle activation), and computed tomography scanning of pelvis and femur. Morphologic measurements included bilateral hip width to femur length ratio, acetabulum abduction, acetabulum anteversion, femoral anteversion, and femoral neck-shaft angles. Sex differences for all variables were examined using independent t-tests. Linear regression was used to assess the ability of each independent variable of interest to predict peak hip adduction during the late swing and stance phase of running. RESULTS Compared to males, females exhibited significantly greater peak hip adduction during both late swing (8.5 ± 2.6° vs 6.2 ± 2.8°, p = 0.04) and stance phases of running (13.4 ± 4.2° vs 10.0 ± 3.2°, p = 0.02). In addition, females exhibited significantly lower hip abductor strength (1.8 ± 0.3 vs 2.0 ± 0.3 Nm/kg, p=0.04), greater femoral neck-shaft angles (134.1 ± 5.0° vs 129.9 ± 4.1°, p=0.01), and greater hip width to femur length ratios than males (0.44 ± 0.02 vs 0.42 ± 0.03, p=0.03). Femoral anteversion was the only significant predictor of peak hip adduction during late swing (r=0.36, p=0.05) and stance (r=0.41, p=0.03). CONCLUSION Our findings highlight the contribution of femur morphology as opposed to hip abductor strength and activation in contributing to hip adduction during running.