Gluteus medius activation timing is related to knee abduction angle during single-leg landing

The purpose of this study was to investigate the relationship between the knee abduction angle (KAA) during single-leg landing and the time parameters of hip abduction strength, as well as gluteus medius (Gmed) activity. Forty-nine collegiate female athletes participated. Kinematic data were collected using 3D motion analysis systems. Hip abduction peak torque during the first 100 ms after the initiation of hip abduction was measured using an isokinetic dynamometer. The activity of Gmed during isokinetic test was evaluated using electromyography (EMG). The rate of EMG rise (RER), which reflects the speed of muscle activation, was calculated using multiple time windows (30, 50, and 75 ms) after EMG onset. Correlation analyses were performed to examine the relationships between KAA and the other parameters. Stepwise multiple regression analysis was then used to identify the factors associated with increased KAA during single-leg landing. The results showed that positive correlations were found between KAA and Gmed's RER, including RER30 (r = 0.39, P < 0.01), RER50 (r = 0.40, P < 0.01), and RER75 (r = 0.36, P = 0.01). Stepwise multiple regression analysis showed that the hip internal rotation angle (ß = 0.461, P < 0.01) and RER50 (ß = 0.375, P < 0.01) were identified as significant predictors of KAA. This study suggests that greater KAA during single-leg landing is associated with rapid Gmed activation.