This study was undertaken to determine the onset, duration, and degree of electromyographic activity in the anterior, middle, and posterior segments of the gluteus medius muscle during functional activities. Fine wire electrodes were inserted into each muscle segment. After a triaxial hip electrogoniometer was applied, each of the 10 subjects performed the activities of walking, crawling, stair ascending and descending, shoetying, sitting, and single limb-standing with forward learning. Raw electromyographic records evaluated on the basis of on-off activity provided results showing that the onset, duration, and degree of activity of the three segments was similar for some activities. Results also established that asynchronous activity occurred for selected functional activities, thereby justifying a three-segment conceptual model of the gluteus medius muscle.