Relationship between hip strength and frontal plane posture of the knee during a forward lunge

Objective: Excessive frontal plane knee movement during forward lunge movements might be associated with the occurrence of knee injuries in tennis. Here, we attempt to determine whether hip muscle strength is related to the frontal plane motion of the knee during a functional lunge movement. Design: A correlational study. Participants: A total of 84 healthy subjects (76 men, 8 women), with no history of knee or lower leg complaints. Interventions: Muscle strength of six hip muscle groups was measured using a handheld dynamometer. Subjects were videotaped during a forward lunge and peak knee valgus or varus angles were determined using a digital video analysis software program. Main outcome measurements: A correlation was examined between hip muscle strength and the amount of frontal plane movement of the knee during a forward lunge. Results: There were no significant differences in hip muscle strength between the valgus group and the varus group during the forward lunge movement. No significant correlation was found between the strength of the assessed hip muscles and the amount of movement into valgus/varus. In the varus group a moderate positive correlation was found between the External Rotation/Internal Rotation force ratio and the amount of knee varus during the forward lunge movement (r = 0.31, p = 0.03). Conclusions: The findings suggest that in healthy subjects hip muscle strength is not correlated to the amount of valgus/varus movement of the knee during a forward lunge. This suggests that other factors (eg, proprioception, core hip stability) might be more important in controlling knee movement during this tennis-specific movement.