FES-propelled cycling of SCI subjects with highly spastic leg musculature

Background:The presence of spasms precludes the use of artificial electrical activation of the muscles to restore mobility. The prospect of using an electrical stimulus that produces motor activation without causing unwanted reflex activation in patients with high levels of spasticity is an appeali ng one. Objective:The purpose of the study was to determine the efficacy of modulated middle frequency alternating current (MFAC) muscle stimulation compared to the conventional method of standard low frequency rectangular pulse (LFRP) stimulation used in cycling of persons with spinal cord injury (SCI) and pronounced spasticity. Methods:To evaluate cycling-relevant differences between stimulation modes, 13 subjects with SCI (ASIA-A), 11 of them with strong spasticity, underwent isometric and cycling measurements using both 20 Hz LFRP and 4 KHz modulated with 50 Hz MFAC. The isometric long-lasting reflex torque response in the quadriceps and hamstrings muscles, and the dynamic work during 1000 sec of ergometric cycling as well as the number of involuntary stops caused by hyperreflexia were recorded. Results:The long-lasting reflex torque response was significantly lower when using MFAC than with LFRP stimulation. During MFAC stimulation work generated was on average 374% higher (p = 0.002) and the number of involuntary stops was on average 32% lower (p < 0.001) than during standard LFRP stimulation-propelled cycling. Conclusion:These findings suggest that MFAC-stimulated cycling of strongly spastic SCI subjects is more effective in terms of generated isometric torque and power than stimulation with LFRP. Thus, more health benefits, e.g., cardiovascular and muscular training and spasticity-decreasing effects, can be expected faster using MFAC instead of LFRP in stimulation-propelled cycling.