Wide-pulse electrical stimulation of the quadriceps femoris allows greater maximal evocable torque than conventional stimulation

Abstract

Purpose: The effectiveness of a neuromuscular electrical stimulation (NMES) program has been shown to be proportional to the maximal evocable torque (MET), which is potentially influenced by pulse characteristics such as duration and frequency. The aim of this study was to compare MET between conventional and wide-pulse NMES at two different frequencies. Methods: MET - expressed as a percentage of maximal voluntary contraction (MVC) torque - and maximal tolerable current intensity (MTCI) were quantified on 71 healthy subjects. The right quadriceps femoris muscle was stimulated with three NMES protocols using different pulse duration/frequency combinations: conventional NMES (0.2 ms/50 Hz; CONV), wide-pulse NMES at 50 Hz (1 ms/50 Hz; WP50) and wide-pulse NMES at 100 Hz (1 ms/100 Hz; WP100). The proportion of subjects reaching the maximal stimulator output (100 mA; MSO) before attaining MTCI was also quantified for each NMES protocol. Results: The proportion of subjects attaining MSO was higher for CONV than WP50 and WP100 (30%, 3% and 4%, respectively; p < 0.001). In subjects who did not attain MSO in any protocol, MET was higher for both WP50 and WP100 than for CONV (45% vs 43% vs 39% MVC; p < 0.001). MTCI was lower for both WP50 and WP100 than for CONV (45, 42, and 77 mA, respectively; p < 0.001) and was also lower for WP100 than for WP50. Conclusion: When compared to conventional NMES, wide-pulse protocols resulted in greater MET, lower MTCI and consequently in a lower proportion of subjects attaining MSO. Overall, this may lead to better NMES training/rehabilitation effectiveness and less practical issues associated with MSO limitations.