Transcutaneous high-frequency alternating current for rapid reversible muscle force reduction below pain threshold

Area of Science:

• Neuroscience
• Rehabilitation Engineering
• Biomedical Engineering

Background:

• Non-invasive methods to control muscle force are crucial for advancing rehabilitation.
• High-frequency alternating current (HFAC) can block nerve conduction but requires invasive procedures and causes pain.
• Transcutaneous HFAC (tHFAC) offers a potential non-invasive alternative to HFAC for nerve conduction block.

Purpose of the Study:

• To investigate the efficacy of transcutaneous high-frequency alternating current (tHFAC) for reducing muscle force.
• To evaluate the effect of varying stimulation frequencies on muscle force reduction using tHFAC.
• To determine if tHFAC can be applied below the pain threshold for clinical use.

Main Methods:

• Ten participants underwent tHFAC stimulation (0.5-12 kHz) applied to median and ulnar nerves via surface electrodes.
• Individual pain thresholds were identified by gradually increasing stimulation amplitude.
• Grip force production was measured during a force-matching task with and without tHFAC applied below the pain threshold.

Main Results:

• Pain threshold current amplitude increased linearly with stimulation frequency.
• Both stimulation frequency and charge injected per phase significantly impacted grip force reduction (p < 0.05).
• tHFAC applied below the pain threshold reduced grip force by up to 40.7% ± 8.1%, with no evidence of fatigue.

Conclusions:

• tHFAC is effective in reducing muscle force when applied below the pain threshold.
• The findings suggest tHFAC has potential clinical viability for rehabilitation applications.
• Further research is needed to fully understand the mechanism of force reduction before widespread clinical adoption.