Reducing Muscle Fatigue with Kilohertz Stimulation: Temporal and Spectral Analysis of Finger Forces

Functional electrical stimulation (FES) is a commonly used method for activating muscles in individuals with neurological impairments. However, traditional FES protocols primarily use low-frequency (LF) stimulation, which evokes synchronous action potentials and induces rapid muscle fatigue. To address this limitation, we applied a recently developed subthreshold high-frequency (HF) stimulation technique to reduce muscle fatigue. Specifically, the HF stimulation was configured with short, charge-balanced pulses of 80 µs at 10 kHz. The HF stimulation, targeting the ulnar and median nerve bundles, was evaluated across three force levels (10%, 25%, and 40% of maximum force). To demonstrate the superiority of the HF stimulation, we also applied LF stimulation for comparison and used voluntary contraction as a baseline. During the experiment, finger forces were recorded and analyzed in both the time and frequency domains. Compared with conventional LF stimulation, HF stimulation effectively reduced muscle fatigue and exhibited temporal and spectral frequency characteristics (i.e., mean force values and median frequency) closer to those of voluntary contractions. These findings underscore the potential of HF stimulation to improve the sustainability and practicality of FES for individuals with neural or muscular conditions.Clinical Relevance- This study investigated the efficacy of subthreshold kilohertz stimulation in reducing muscle fatigue during prolonged use at varying force levels, potentially facilitating the applications of kilohertz stimulation in clinical settings.