The relationship of hip strength and dynamic knee valgus during single leg squat in physically active females

Background: Single leg squat (SLS) is an important motion commonly observed in sports. Excessive dynamic knee valgus (DKV) during SLS may increase non-contact knee injury risks particularly in physically active females. As muscular strength plays crucial role in controlling DKV, the present study aims to evaluate the correlation between hip strength and knee frontal plane angle during SLS among females with and without excessive DKV. Methods: Thirty-four volunteers were allocated to the valgus (n = 17) and non-valgus (n = 17) groups. Their motions during SLS at 45 degrees and 60 degrees knee flexion were captured and analyzed using three-dimensional motion analysis system. Isokinetic hip strength was examined at 180 degrees/s in flexion, extension, abduction, and adduction for both legs. Pearson's correlation test was computed to evaluate the relationship between hip strength and knee angle during SLS. Findings: Non-dominant hip extensor strength (r = -0.56, p = 0.02) and dominant hip adductor strength (r = -0.51, p = 0.04) were significantly related to the knee frontal plane angle during 45 degrees SLS among those without DKV. Meanwhile, those with DKV showed a significant relationship between the knee frontal plane angle for both legs and non-dominant hip abductor strength during 60 degrees SLS. Interpretation: Both groups demonstrated the relationship of hip strength on knee frontal plane angle during SLS, whereby increased hip strength may minimize excessive DKV. Those with excessive DKV should train to strengthen their hip abductor to reduce knee valgus particularly during deep squats.