Impact of isometric hip abduction angle on isolated hip abductor muscle work in gluteus medius weakness

This cross-sectional study aimed to investigate how different hip abduction angles influence hip abduction torque and muscle activation of the gluteus medius (Gmed) and tensor fasciae latae (TFL) during side-lying hip abduction in individuals with Gmed weakness. Twenty-five individuals with Gmed weakness participated in this study. Participants performed isometric hip abduction in a side-lying position at four joint angles (−15°, 0°, 15°, and 30°). Hip abduction torque was measured using an isokinetic dynamometer, while surface electromyography was used to simultaneously record Gmed and TFL muscle activities. The Gmed/TFL activity ratio was calculated to examine relative activation patterns. Hip abduction torque was normalized to body weight. Peak hip abduction torque was greatest at −15°, followed by 0°, 15°, and 30°. Electromyographic analysis showed that Gmed activity was greater at −15° and 0° than at 30°, whereas TFL activity was lowest at 30°. Although no significant pairwise differences were detected, the Gmed/TFL activity ratio tended to increase with increasing hip abduction angle, reaching its highest value at 30°. Hip abduction angle influences hip abduction torque and muscle activation during side-lying hip abduction in individuals with Gmed weakness. A more adducted starting position was associated with greater torque, whereas a more abducted position showed lower TFL activity and higher Gmed/TFL ratios; thus, hip abduction angle may be considered in rehabilitation, with caution.