The Relationship of Anticipatory Gluteus Medius Activity to Pelvic and Knee Stability in the Transition to Single-Leg Stance.

Background: The knee abduction moment in a weight-bearing limb is an important risk factor of conditions such as patellofemoral pain and knee osteoarthritis. Excessive pelvic drop in single-leg stance can increase the knee abduction moment. The gluteus medius muscle is crucial to prevent pelvic drop and must be activated in anticipation of the transition from double-leg to single-leg stance.

Objective: To examine the relationship of anticipatory activity of the gluteus medius to pelvic drop and knee abduction moment.

Design: Observational, cross-sectional correlational study.

Setting: Research laboratory.

Participants: Twenty female adults (mean age 22.6 years, standard deviation 2.5) were recruited and fully participated. Participant selection was limited to healthy women who did not have a history of knee and ankle ligament injuries, any indication of knee, hip, and/or low back pain, and/or knowledge of the proper squat technique.

Methods: Participants performed 16 single-leg mini squats on their nondominant leg.

Main Outcome Measures: The onset and magnitude of anticipatory gluteus medius activity were measured in relation to toe-off of the dominant leg during the transition from double-leg to single-leg stance. Preplanned correlations between anticipatory gluteus medius onset and its activation magnitude, pelvic obliquity, and knee abduction moment were examined.

Results: The magnitude of anticipatory gluteus medius activity was significantly correlated with the knee abduction moment (rs (18) = -0.303, P < .001) and pelvic obliquity (rs (18) = 0.361, P < .001), whereas gluteus medius onset was not significantly correlated with either knee abduction moment or pelvic obliquity.

Conclusions: The amount of gluteus medius activity is more important for controlling knee and pelvic stability in the frontal plane than the onset of activation.