Differences in current amplitude evoking leg extension in individuals with spinal cord injury

OBJECTIVES: To investigate the effects of regional thigh composition that result in different responses to current amplitude among individuals with spinal cord injury (SCI) during applications of surface neuromuscular electrical stimulation (NMES) to evoke dynamic leg extension. DESIGN: Cross-sectional. SETTINGS: Academic Settings. METHODS: Five males with chronic motor complete SCI completed 3 visits of NMES to determine the current amplitude required to evoke full knee extension. The participants underwent magnetic resonance imaging of both thighs to measure skeletal muscle cross-sectional area (CSA), thigh subcutaneous adipose tissue (SAT) and intramuscular fat (IMF). Applicants were classified into high (n = 3) and low-responders (n = 2) based on the determined current amplitude. RESULTS: The low-responders required 48-59% greater current amplitude to complete the same task as the high-responders. Low-responders had greater thigh SAT CSA (51-56%) than the high-responders with SCI. After adjusting to whole thigh CSA, IMF CSA was significantly greater in the low- responders; whereas skeletal muscle CSA was lower compared to the high-responders. CONCLUSION: The findings suggest that thigh SAT and IMF act as insulation against propagation of current during surface NMES applications in individuals with SCI.