Hip Muscle Activity during Isometric Contraction of Hip Abduction

[Purpose] This study aimed to determine the effect of varying hip flexion angle on hip muscle activity during isometric contraction in abduction. [Subjects] Twenty-seven healthy men (mean age=21.5 years, SD=1.2) participated in this study. [Methods] Surface electromyography (EMG) was recorded of the upper portion of the gluteus maximus (UGM), lower portion of the gluteus maximus (LGM), tensor fasciae latae (TFL), and gluteus medius (GMed) during isometric contraction under two measurement conditions: hip flexion angle (0, 20, 40, 60, and 80 degrees) and abduction of the hip joint at 20, 40, 60, and 80% maximum strength. Integrated EMG (IEMG) were calculated and normalized to the value of maximum voluntary contraction (MVC). [Results] Results indicated that the IEMG of both the UGM and LGM increased significantly with increases in hip flexion angle, whereas the IEMG of the TFL decreased significantly. The maximum activities of the UGM and the LGM were 85.7 ± 80.8%MVC and 38.2 ± 32.9%MVC at 80 degrees of hip flexion, respectively, and that of the TFL was 71.0 ± 39.0%MVC at 40 degrees of hip flexion. [Conclusion] The IEMG of the GMed did not change with increases in hip flexion angle. Hip flexion angle affected the activity of the GM and TFL during isometric contraction in abduction.