A Generic Sequential Stimulation Adapter for Reducing Muscle Fatigue during Functional Electrical Stimulation.

Gongkai Ye,Kei Masani,Austin J Bergquist,Saima S Ali,Milos R Popovic

doi:10.3390/s21217248

Abstract

Background: Clinical applications of conventional functional electrical stimulation (FES) administered via a single electrode are limited by rapid onset neuromuscular fatigue. “Sequential” (SEQ) stimulation, involving the rotation of pulses between multiple active electrodes, has been shown to reduce fatigue compared to conventional FES. However, there has been limited adoption of SEQ in research and clinical settings. Methods: The SEQ adapter is a small, battery-powered device that transforms the output of any commercially available electrical stimulator into SEQ stimulation. We examined the output of the adaptor across a range of clinically relevant stimulation pulse parameters to verify the signal integrity preservation ability of the SEQ adapter. Pulse frequency, amplitude, and duration were varied across discrete states between 4 and 200 Hz, 10 and100 mA, and 50 and 2000 μs, respectively. Results: A total of 420 trials were conducted, with 80 stimulation pulses per trial. The SEQ adapter demonstrated excellent preservation of signal integrity, matching the pulse characteristics of the originating stimulator within 1% error. The SEQ adapter operates as expected at pulse frequencies up to 160 Hz, failing at a frequency of 200 Hz. Conclusion: The SEQ adapter represents an effective and low-cost solution to increase the utilization of SEQ in existing rehabilitation paradigms.

Highlights

During voluntary muscle contractions, motor units are recruited asynchronously with respect to each other
The relatively high motor unit discharge rates associated with conventional functional electrical stimulation (FES) increases the metabolic demand placed on recruited motor units, contributing to greater levels of neuromuscular fatigue compared to voluntary contractions [5,6,7,8]
The SEQ adapter receives electrical pulses from the output of a single stimulation channel and sequentially rotates the delivery of those pulses, pulse-by-pulse, among four separate outputs instead of programming four separate channels. Using this SEQ adapter, we previously demonstrated that using it to apply SEQ stimulation reduced the neuromuscular fatigue of quadriceps femoris muscle contractions compared to conventional FES, and that each SEQ electrode activated relatively distinct motor unit populations [20]

Summary

Introduction

Motor units are recruited asynchronously with respect to each other. Conventional FES generates muscle contractions predominantly by the synchronous depolarization of motor axons beneath the stimulating electrodes [2]. Such synchronous motor unit recruitment means that stimulation frequencies in the range of. To prevent rapid neuromuscular fatigue associated with FES-evoked contractions, researchers have developed a promising FES technique which mimics the asynchronous motor unit recruitment pattern that occurs during voluntary contractions. This technique involves the “sequential” rotation of stimulation pulses between multiple active electrodes positioned over the muscle belly (SEQ). Conclusion: The SEQ adapter represents an effective and low-cost solution to increase the utilization of SEQ in existing rehabilitation paradigms

Methods

Results

Discussion

Conclusion