A method for better positioning bipolar electrodes for lower limb EMG recordings during dynamic contractions

Area of Science:

• Biomechanics
• Human Physiology
• Electrophysiology

Background:

• High-quality EMG acquisition requires careful electrode placement away from shifting muscle innervations and tendons during dynamic contractions.
• Existing guidelines like SENIAM may not always provide optimal electrode positions for all lower limb muscles during dynamic movements.

Purpose of the Study:

• To develop and validate a methodology for identifying optimal electrode positions for superficial EMG of lower limb muscles during dynamic contractions.
• To compare signal quality from SENIAM-recommended sites versus newly identified optimal sites.

Main Methods:

• Eight female volunteers performed maximum isometric contractions of vastus lateralis, gastrocnemius medialis, peroneus longus, and tibialis anterior muscles.
• Bipolar electrodes were used, with initial placement based on SENIAM guidelines.
• Signal density, linear envelopes, RMS values, motor point location, and the position and shift of the innervation zone (IZ) during contractions were analyzed to determine optimal sites.

Main Results:

• Optimal electrode positions varied by muscle: vastus lateralis (66% muscle length), peroneus longus (25% muscle length), tibialis anterior (47.5% muscle length), and gastrocnemius medialis (38% muscle length).
• Optimal sites for vastus lateralis and peroneus longus were similar to SENIAM locations.
• Optimal site for tibialis anterior differed from SENIAM, and SENIAM lacks specific guidance for gastrocnemius medialis.

Conclusions:

• The proposed methodology offers a systematic approach to identify superior electrode placements for EMG signal acquisition during dynamic lower limb movements.
• This method enhances EMG signal quality, crucial for accurate interpretation of human movement.
• Adopting this methodological step is recommended for all EMG studies involving dynamic contractions.