Recording Of Surface Electromyogram From The Hip Adductor Muscles

Abstract

The functional roles and activation pattern of the hip adductor muscles (HA) have yet to be fully understood, although the importance of HA during human movements has been suggested in previous studies. This problem could be caused by the difficulty in recording surface electromyogram (EMG) from individual HA, due to complex anatomical properties that interfere with the determination of proper electrode location. To grasp detailed anatomical properties under the skin surface, medical imaging techniques such as magnetic resonance imaging (MRI) and ultrasonography (US) would be useful. PURPOSE: The purposes of the present study were to clarify the anatomical properties of individual HA and to test the validity of electrode location for surface EMG for the individual HA determined using medical imaging techniques. METHODS: Experiment 1: Consecutive axial MRI was obtained from the thigh for 45 healthy men. Areas of regions where the two selected individual HA, i.e., the adductor magnus (AM) and adductor longus (AL) muscles, identified under the skin surface (superficial regions) were measured from the obtained MRI. Experiment 2: Six healthy men performed slow pedaling at 150 W. During exercise, surface and needle EMG were simultaneously recorded from AM and AL, respectively. Electrode locations of surface EMG were determined using US. Electrodes for needle EMG were inserted near the surface electrodes. Activation patterns and peak timing during a crank cycle were compared between surface and needle EMGs for AM and AL. RESULTS: Experiment 1: Areas of superficial regions of AM and AL were 27.8 ± 6.2 cm2 and 35.4 ± 7.9 cm2, respectively. Experiment 2: Similar activation patterns (r = 0.955-0.994 for AM, r = 0.851-0.980 for AL) and no significant differences (p > 0.05) in peak timing (79.5 ± 35.0° in surface EMG and 76.8 ± 32.7° in needle EMG for AM, 266.0 ± 59.4° in surface EMG and 277.3 ± 54.0° in needle EMG for AL, top of crank cycle defined as 0°) during a crank cycle were obtained between surface and needle EMGs for both AM and AL. CONCLUSION: These results suggest that AM and AL have sufficiently large superficial regions to set the electrodes of surface EMG and that electrode locations determined using US are valid for recording surface EMGs from AM and AL.