Muscle activity and coordination in the normal shoulder. An electromyographic study

Area of Science:

• Biomechanics
• Human Physiology
• Kinesiology

Background:

• The shoulder joint's complex structure necessitates intricate muscle coordination for stability.
• Understanding muscle activation patterns is crucial for diagnosing and treating shoulder pathologies.

Purpose of the Study:

• To investigate muscle activity and coordination in the shoulder during standardized loaded movements.
• To analyze the role of specific shoulder muscles as stabilizers during various rotations and flexions.

Main Methods:

• Electromyography (EMG) was used to record muscle activity in ten shoulders of five healthy subjects.
• Standardized loaded movements (flexion, extension, abduction, rotations) were performed at different abduction angles.
• Surface and intramuscular electrodes captured EMG signals from subscapularis, supraspinatus, infraspinatus, pectoralis major, deltoid (anterior, middle, posterior), and latissimus dorsi.

Main Results:

• Simultaneous muscle activity was observed in both agonist and antagonist muscles during movements.
• The infraspinatus, subscapularis, and latissimus dorsi demonstrated stabilizing roles during flexion.
• The subscapularis acted as a stabilizer during external rotation, and with the supraspinatus during extension.

Conclusions:

• Muscle coordination, involving co-contraction of antagonistic muscles, is essential for shoulder joint stabilization.
• Specific muscles like the infraspinatus, subscapularis, and latissimus dorsi play key roles in stabilizing the shoulder during different movements.