Lower limb muscle activity under full and partial towing assistance in sprint running

This study investigated how different levels of sprint assistance influence neuromuscular activity and performance. Concerns exist that full assistance may reduce active muscle engagement due to passive contributions. Thirteen male athletes from various sports performed 30-m sprints under three conditions: unassisted, partially assisted, and fully assisted, using a motorised towing device. Surface electromyography recorded activity of five lower limb muscles (rectus femoris, vastus lateralis, semitendinosus, biceps femoris, and gluteus maximus), while spatiotemporal parameters were measured over the final 10 m using Optojump. Sprint times were significantly improved in both assisted conditions compared to unassisted sprints (partial: -3.4%, full: -2.8%; p < 0.01), primarily due to increased stride length (p < 0.001), longer flight time, and shorter contact time (p < 0.05 for both), while stride frequency remained unchanged. Contrary to hypothesis, EMG analyses revealed no statistically significant differences in muscle activity between conditions, despite improved performance and the potential contribution of passive propulsion. Large effect sizes (d > 0.8) were briefly observed, in a muscle-dependent manner, at discrete points of the gait cycle. These findings suggest that assisted sprinting enhances performance without reducing neuromuscular demands, although the results should be interpreted in light of the athletes' inexperience with assisted running.