Influences of hip external rotation strength on knee mechanics during single-leg drop landings in females

Background To determine the influence of hip external rotation strength on kinematic and kinetic variables during single-leg drop landings. Methods Females were divided into strong and weak groups based on isometric hip external rotation strength and lower extremity flexion–extension and varus–valgus kinematics and kinetics were evaluated during single-legged 40 cm drop landings. Findings Hip external rotation strength had no effect on sagittal or frontal plane angular motion throughout the landing cycle at the hip and knee. The strong group generated a statistically significant decrease in the peak vertical ground reaction force and external knee flexor moment. The weak group produced a greater external knee adduction moment, net knee anterior shear joint reaction force, and a greater hip external adduction moment. Interpretation Subjects with greater hip and quadriceps/hamstring strength exhibited a significant decrease in the vertical ground reaction force and external knee adduction and flexor moments. Hip and knee strength appear to relate to differences in high risk landing strategies.