Muscle activity while running at 20%-50% of normal body weight

Little information exists on how body weight (BW) support influences running biomechanics. The study aim was to determine how reducing BW by 50%-80% influences muscle activity while running at different speeds. Subjects (n = 7) ran at 100%, 115%, 125% of preferred speed at 100%, 50%, 40%, 30%, 20% of BW per speed. Average (AVG) electromyography of the rectified signal was compared (within subject design; 3-speeds × 5-BW, repeated measures ANOVAs; biceps femoris [BF], rectus femoris [RF], tibialis anterior [TA], gastrocnemius [GA]). RF, BF, and GA AVG were not influenced by BW-speed interaction (p >.05) and increased across speeds (p <.05). RF and GA AVG signal was reduced as BW was reduced (p <.05), but BF only tended to be different (p =.08). TA was influenced by BW-speed interaction (p <.05) with EMG decreasing across BW (p <.05) while increasing across speeds except at 100% BW. Overall, muscle activity increased with speed and decreased by BW reductions.