Muscle Activity During Backward And Forward Running At Reduced Body Weight

Abstract

Body weight (BW) support during locomotion is used for both forward and backward locomotion. However, muscle activity during locomotion in different directions at different levels of BW support is not known. PURPOSE: To investigate muscle activity during backward (BR) and forward (FR) running at different BW support conditions. METHODS: Ten subjects (23.1±3.5 yrs) completed BR and FR on a lower body positive pressure treadmill; selecting a preferred speed for different BW support conditions (0%, 20%, 40%, 60%, and 80% of BW). Muscle activity from the rectus femoris (RF), biceps femoris (BF), tibialis anterior (TA), and gastrocnemius (GA) were measured and averaged across 15 s (zero offset removed, full-wave rectified). In addition, rating of perceived exertion (RPE), preferred stride frequency (PSF), and preferred speed (PS) were measured. All parameters were analyzed using 2 (direction) x 5 (BW) repeated measures ANOVA (α = 0.05). When an interaction effect was observed, post hoc analysis was performed using a Fisher’s protected least significant difference multiple comparison test (α = 0.05). RESULTS: Muscle activity (BF, TA, and GA), RPE, PSF, and PS were not influenced by the interaction of direction and BW support (P>0.05). BF, TA, and GA were not different between directions (P>0.05) but were different between BW support conditions (P<0.05). RF was influenced by the interaction of direction and BW support (P<0.05). For example, RF during BR at 0% BW support condition was significantly higher than that of BR at 40% (P<0.05), 60% (P<0.05), and 80% (P<0.05) BW support conditions. RF, BF, TA, and GA during BR were lower with increasing BW support (e.g., a decrease of 33%~60% between 80% and 0% BW support conditions). RPE during BR and FR were lower with increasing BW support (P<0.05) regardless of direction of locomotion (P>0.05). PSF and PS were different between directions (P<0.05) and between BW support conditions (P<0.05). PSF during BR and FR were lower and PS higher with increasing BW support. PSF during BR was 6%~9% higher than that of FR. PS during BR was 24%~31% lower than that of FR (e.g., 8.9±1.7 km/h vs. 11.9±3.2 km/h for BR and FR at 80% BW support condition, respectively). CONCLUSION: BW support influenced muscle activity whereas direction of locomotion did not even though slower speeds were selected BR vs. FR.