Muscle firing order during active prone hip extension.

This research was submitted in partial fulfillment for a Master of Science degree from Northwestern University. The purpose of this study was to determine if persons without a history of low back dysfunction use a statistically consistent muscle firing order of left erector spinae, right erector spinae, right gluteus maximus, and right biceps femoris during active right prone hip extension. Twenty healthy subjects each made 30 hip extension movements while prone. The onset of EMG activity in each of the four muscles was measured for each trial. A Friedman Two-way Analysis of Ranks revealed no significant difference in mean onset times of left erector spinae, right erector spinae, right gluteus maximus, and right biceps femoris muscles. This finding reflects the variability in the relative onset times among the four muscles both within and between subjects. The absence of a consistent firing order indicates that active prone hip extension can be performed in a wide variety of ways in healthy subjects. J Orthop Sports Phys Ther 1990;12(1):2-9.