Muscle activity of deep hip muscles across joint positions and elevation phases during side-lying hip abduction

Introduction Hip abductor dysfunction is associated with various musculoskeletal disorders, such as knee overuse injury, patellofemoral pain syndrome, and hip osteoarthritis. Thus, hip abduction exercise is used to improve hip muscle performance. Notably, deep hip muscles might be effectively activated during the hip internal rotation (IR) position. Moreover, it is hypothesized that hip abduction combined with hip IR might activate the deep hip muscles and minimize tensor fascia latae (TFL) activation. Objective This study aimed to investigate the percentage maximum voluntary isometric contraction (%MVIC) and the activity ratio of the gluteus muscles in relation to the activity of the TFL—including the gluteus minimus (GMin), piriformis, and gluteus medius (GMed)—across different hip positions during side-lying hip abduction. Methods Twelve healthy men performed hip abduction exercises in nine hip joint positions. The muscle activities of the lower extremities, including the anterior and posterior segments of the GMin (GMin-a and GMin-p) and piriformis, GMed, and TFL, were recorded via surface and fine-wire electromyography. Results The %MVIC of the GMin-p and GMed was highest in hip extension and IR (EIR) position during the late concentric phase (GMin-p 54.7 ± 27.2 %MVIC; GMed 59.2 ± 36.1 %MVIC; P < 0.05). No significant difference was observed in the %MVIC of TFL (lower in the hip internal rotation position). The relative activation ratios (RARs) of the GMin-p and GMed to TFL were highest in hip position involving IR during the early concentric or late eccentric phases (GMin-p 3.80 ± 3.65; GMed 2.62 ± 1.72; <0.05). Conclusions Hip abduction during the late concentric phase with EIR position caused maximal hip abductor activity. Conversely, hip abduction during the early concentric phase involving the IR position selectively activated the GMin-p and GMed while minimizing TFL activation.