Relationships between Knee Valgus, Hip-Muscle Strength, and Hip-Muscle Recruitment during a Single-Limb Step-Down

CONTEXT: Reduced strength and activation of hip muscles might correlate with increased weight-bearing knee valgus. OBJECTIVE: To describe relationships among frontal-plane hip and knee angles, hip-muscle strength, and electromyographic (EMG) recruitment in women during a step-down. DESIGN: Exploratory study. SETTING: Laboratory. PARTICIPANTS: 20 healthy women 20 to 30 years of age. INTERVENTIONS: Frontal-plane hip and knee angles were measured. Gluteus maximus and medius recruitment were examined with surface EMG. Hip-abduction and -external-rotation strength were quantified with handheld dynamometry. MAIN OUTCOME MEASUREMENTS: The authors analyzed correlation coefficients between knee and hip angles, gluteus maximus and medius EMG, and hip-abduction and -external-rotation strength. RESULTS: Hip-adduction angles (r = .755, P = .001), gluteus maximus EMG (r = -.451, P = .026), and hip-abduction strength (r = .455, P = .022) correlated with frontal-plane projections of knee valgus. CONCLUSIONS: Gluteus maximus recruitment might have greater association with reduced knee valgus in women than does external-rotation strength during step-down tasks. Gluteus medius strength might be associated with increased knee valgus.