Muscle Fatigue Post-stroke Elicited From Kilohertz-Frequency Subthreshold Nerve Stimulation

Area of Science:

• Neuroscience
• Biomedical Engineering
• Rehabilitation Medicine

Background:

• Rapid muscle fatigue is a major limitation for functional electrical stimulation (FES) in individuals with motor impairments.
• Novel transcutaneous nerve stimulation techniques are needed to improve FES sustainability and clinical utility.

Observation:

• A novel high-frequency (HF) nerve stimulation technique (12.5 kHz, 60-μs pulses) was compared to conventional low-frequency (LF) stimulation (30 Hz, 600-μs pulses) in a chronic stroke survivor.
• Muscle fatigue was assessed by finger flexion force and high-density electromyography (EMG) during intermittent stimulation trains.
• Initial contraction forces were matched between HF and LF modes to ensure a fair comparison.

Findings:

• HF stimulation resulted in slower force decline and higher force plateau compared to LF stimulation, indicating more sustainable muscle force.
• Force fluctuations increased more slowly and were smaller with HF stimulation, suggesting less synchronized muscle fiber activation.
• The force-EMG ratio was higher with HF stimulation, indicating improved muscle activation efficiency.

Implications:

• The HF nerve stimulation technique effectively reduces muscle fatigue in stroke survivors.
• This method enhances muscle activation efficiency, potentially improving neurorehabilitation outcomes.
• The findings suggest that HF stimulation could broaden the clinical applications of FES in populations with motor impairments.