High-density surface electromyography provides reliable estimates of motor unit behavior

Area of Science:

• Neuromuscular physiology
• Biomedical engineering
• Motor control

Background:

• High-density surface electromyography (HDEMG) offers a non-invasive method to study motor unit behavior.
• Assessing the reliability of HDEMG-derived measures is crucial for its application in research and clinical settings.

Purpose of the Study:

• To evaluate the intra- and inter-session reliability of motor unit characteristics and muscle fiber properties estimated using HDEMG.
• To determine the consistency of these measures across different force levels and multiple recording sessions.

Main Methods:

• Ten healthy participants performed isometric knee extensions at various submaximal efforts (10-70% MVC).
• Motor unit discharge timings were extracted from HDEMG signals using a decomposition algorithm.
• Reliability of motor unit number, discharge rate, inter-spike interval variation, conduction velocity, and amplitude was assessed using intra-class correlation coefficients (ICCs).

Main Results:

• High to excellent reliability (ICCs > 0.8) was observed for most motor unit characteristics across sessions and force levels.
• The coefficient of variation of inter-spike intervals (CoVisi) showed poor reliability (ICC < 0.6).
• High pulse-to-noise ratios (45.1-47.6 dB) indicated accurate decomposition (>95% accuracy).

Conclusions:

• HDEMG provides reliable non-invasive estimates of motor unit behavior and muscle properties within and across sessions.
• These findings support the use of HDEMG for characterizing motor units in longitudinal studies, enabling robust tracking of changes over time.