Effect of stimulation frequency and intensity on skeletal muscle fatigue during repetitive electrical stimulation

The goal of this project was to study strategies to improve muscle performance during functional electrical stimulation (FES). Specific Aim 1 compared isometric muscle performance during repetitive stimulation, with 3 different combinations of frequency and pulse duration to generate the same initial peak force: Protocol #1 used a long-pulse duration (600-mus) and low-frequency; Protocol #2 used a medium-frequency (30-Hz) and medium-pulse duration; and Protocol #3 used high-frequency (60-Hz) and short-pulse duration. The results showed that if the frequency and intensity are kept constant during FES, repetitive stimulation using a low-frequency, long-pulse-duration (Protocol #1) maximized muscle performance. Specific Aim 2 compared isometric muscle performance during repetitive electrical stimulation using 3 different strategies: constant pulse-duration and stepwise increases in frequency (frequency-modulation), constant frequency and stepwise increases in pulse-duration (pulse-duration-modulation), and constant frequency and pulse-duration (no-modulation). The results showed that frequency-modulation can help improve muscle performance during FES.