Electromyographic analysis: shoulder muscle activity revisited

Area of Science:

• Biomechanics
• Neuroscience
• Orthopedics

Background:

• Understanding healthy shoulder muscle activity is crucial for treating shoulder pathologies.
• Existing data on normal shoulder muscle activation patterns are inconsistent.
• Electromyography (EMG) is a key tool for assessing muscle function.

Purpose of the Study:

• To evaluate muscle activity patterns in healthy shoulders using surface and fine-wire EMG.
• To assess the clinical suitability of EMG methods, focusing on pain and practicality.
• To identify the role of specific muscles, like the subscapularis, in shoulder movements.

Main Methods:

• Surface and fine-wire EMG were used on 11 healthy subjects (2 female/9 male, mean age 28).
• EMG activity was recorded for 14 muscles during 8 standardized planar shoulder movements.
• Pain was assessed using a visual analogue scale throughout the procedure.

Main Results:

• The subscapularis muscle plays a significant role in shoulder abduction and forward flexion.
• EMG measurements, particularly fine-wire EMG, demonstrated high failure rates (up to 32%).
• Pain was not a significant limiting factor during the EMG testing procedures.

Conclusions:

• The subscapularis is identified as a major contributor to abduction and forward flexion in healthy shoulders.
• The motion analysis system and fine-wire electrodes showed a propensity for failure.
• Pain associated with EMG procedures does not hinder their clinical application.