Study Design: Experimental laboratory study. Objectives: To measure the activation patterns (onset and magnitude) of the abdominal muscles during a standing long jump using wire and surface electromyography. Background: Activation patterns of the abdominal muscles, especially the deep muscles such as the transversus abdominis (TrA), have yet to be examined during full-body movements such as jumping. Methods: Thirteen healthy men participated. Wire electrodes were inserted into the TrA with the guidance of ultrasonography, and surface electrodes were attached to the skin overlying the rectus abdominis (RA) and external oblique (EO). Electromyographic signals and video images were recorded while each subject performed a standing long jump. The jump task was divided into 3 phases: preparation, push-off, and float. For each muscle, activation onset relative to the onset of the RA and normalized muscle activation levels (percent maximum voluntary contraction) were analyzed during each phase. Comparisons between muscles and phases were assessed using 2-way analyses of variance. Results: The onset times of the TrA and EO relative to the onset of the RA were −.13 ± 0.17 seconds and −.02 ± 0.07 seconds, respectively. Onset of TrA activation was earlier than that of the EO. The activation levels of all 3 muscles were significantly greater during the push-off phase than during the preparation and float phases. Conclusion: Consistent with previously published trunk-perturbation studies in healthy persons, the TrA was activated prior to the RA and EO. Additionally, the highest muscle activation levels were observed during the push-off phase. J Orthop Sports Phys Ther 2013;43(8):577–582. Epub 11 June 2013. doi:10.2519/jospt.2013.4420

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.