Reduced Muscle Fatigue Using Continuous Subthreshold Kilohertz Stimulation of Peripheral Nerves

TL;DR

This study demonstrates that continuous high-frequency subthreshold electrical stimulation of peripheral nerves can significantly reduce muscle fatigue and sustain muscle activation better than traditional low-frequency stimulation, improving functional electrical stimulation outcomes.

Contribution

Introduces a novel high-frequency subthreshold stimulation method that mimics voluntary muscle activation and reduces fatigue compared to conventional low-frequency FES.

Findings

HF stimulation maintains force output longer than LF stimulation.

HF stimulation evokes more dispersed muscle activation similar to voluntary contractions.

HF stimulation significantly reduces muscle fatigue in comparison to traditional methods.

Abstract

Functional electrical stimulation (FES) is a prevalent technique commonly used to activate muscles in individuals with neurological disorders. Traditional FES strategies predominantly utilize low-frequency (LF) stimulation, which evokes synchronous action potentials, leading to rapid muscle fatigue. To address these limitations, we introduced a subthreshold high-frequency (HF) stimulation method that employed continuous, charge-balanced subthreshold current pulses at kilohertz frequencies, designed to evoke motor unit (MU) activation similar to voluntary activation. We evaluated the effectiveness of HF stimulation on the reduction of muscle fatigue across different force levels (10 %, 25 %, and 40 % of maximum force). The HF stimulation utilized continuous charge-balanced, short pulses of 80 {\mu}s (at a 10 kHz frequency) targeted the ulnar/median nerve bundles. We compared the fatigue effects with conventional LF stimulation and voluntary muscle contractions. Our results indicated that HF stimulation maintained more sustained force outputs and muscle activation over a prolonged time compared with LF stimulation. The HF stimulation also evoked a more dispersed muscle activation pattern, similar to voluntary muscle contractions. These findings suggest that HF stimulation can significantly enhance the sustainability of muscle contractions and reduce muscle fatigue, potentially improving the efficacy and applicability of FES in clinical and home-based settings for individuals with neurological impairments.