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Timing and Relative Intensity of Hip Extensor and Abductor Muscle Action During Level and Stair Ambulation: An EMG Study

Ms. Lyons is a physical therapist specializing in EMG testing at Group Health Cooperative of Puget Sound, Central Hospital, Seattle, WA, 98112 (USA). This study was completed in partial fulfillment of the requirements for her Master of Science in Physical Therapy degree, University of Southern California, Rancho Los Amigos Hospital, Downey, CA.
Dr. Perry is Director, Pathokinesiology Laboratory, Rancho Los Amigos Hospital, Downey, CA 90242, and Professor of Orthopaedics, University of Southern California.
Ms. Gronley is Research Physical Therapist, Pathokinesiology Laboratory, Rancho Los Amigos Hospital.
Mr. Barnes is Computer Programmer, Pathokinesiology Laboratory, Rancho Los Amigos Hospital.
Mr. Antonelli is Co-director, Pathokinesiology Laboratory, Rancho Los Amigos Hospital.

The timing and relative intensity of electromyographic activity of hip abductor and extensor muscles were recorded during free and fast velocity walking and during ascent and descent of stairs. Eleven healthy subjects were tested using fine wire electrodes to record the electromyographic activity. Data were quantified by normalizing all electromyographic activity during gait with electromyographic activity occurring during a sustained maximum isometric effort resisted either manually or with a dynamometer. The results indicated that the hip extensor muscles had different phasic patterns and moments of peak activity. During level walking, the semimembranosus and long head of the biceps femoris muscles displayed the greatest swing phase activity (beginning in mid-swing). The adductor magnus muscle followed with its onset in terminal swing. Both this muscle and the gluteus maximus were the principal hip extensors active during the loading response. For ascending stairs, the lower portion of the gluteus maximus muscle proved to be the main hip extensor during the loading response and mid-stance. The findings also showed that the upper portion of the gluteus maximus muscle functioned more like the gluteus medius muscle than the lower portion of the gluteus maximus muscle during both level and stair walking.

Key Words: Electromyography • Gait • Hip • Muscles

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