Coherence between surface electromyograms is influenced by electrode placement in hand muscles

Area of Science:

• Biomechanics
• Neuroscience
• Human Movement Science

Background:

• Surface electromyography (EMG) is widely used to assess muscle activation.
• Accurate EMG signal interpretation relies on optimal electrode placement.
• Innervation zones, where motor nerves connect to muscles, can influence EMG signal characteristics.

Purpose of the Study:

• To investigate the influence of electrode location relative to the innervation zone on EMG-EMG coherence between hand muscles.
• To determine if specific electrode placements enhance or diminish coherence measures during a pinch task.

Main Methods:

• Multi-channel surface EMGs were recorded from first dorsal interosseous (FDI) and abductor pollicis brevis (APB) muscles during a pinch task.
• Electrodes were placed over innervation zones and at 15mm proximal and distal locations.
• Coherence spectra were calculated for EMG pairs from different electrode configurations and force levels (2N and 3.5N).

Main Results:

• A significant main effect of electrode location on maximal coherence was found (ANOVA, p=0.001).
• Maximal coherence increased by 58.1% when electrodes avoided innervation zones compared to when centered over them (0.18±0.03 vs. 0.11±0.02).
• These findings were consistent across tested force levels and frequency bands (1-15Hz and 16-32Hz).

Conclusions:

• Electrode location relative to the muscle's innervation zone critically influences EMG-EMG coherence.
• Optimal electrode placement, avoiding innervation zones, can yield higher and potentially more reliable coherence measures.
• Careful consideration of electrode positioning is essential for accurate EMG analysis in hand muscles.