Rotator cuff muscles perform different functional roles during shoulder external rotation exercises

Area of Science:

• Biomechanics
• Human Movement Science
• Musculoskeletal Research

Background:

• Understanding shoulder muscle function is crucial for rehabilitation and injury prevention.
• The rotator cuff (RC) muscles play a vital role in shoulder joint stability and movement.
• Differential muscle recruitment patterns during external rotation tasks require further investigation.

Purpose of the Study:

• To compare shoulder muscle activity during external rotation with varying arm support.
• To determine how changing support influences muscle recruitment, especially in the RC muscles.
• To investigate the specific functional roles of infraspinatus, supraspinatus, and subscapularis during rotation and stabilization.

Main Methods:

• Electromyographic (EMG) recordings from seven shoulder muscles using surface and indwelling electrodes.
• Dynamic shoulder external rotation task at 90° abduction in 14 healthy participants.
• Conditions included fully supported, partially supported, and unsupported arm positions.

Main Results:

• Infraspinatus was the primary muscle for external rotation torque.
• Supraspinatus, deltoid, upper trapezius, and serratus anterior primarily functioned in support/stabilization roles.
• Subscapularis showed minimal contribution to joint stability during this task.

Conclusions:

• The rotator cuff muscles have distinct functional roles during dynamic external rotation.
• Infraspinatus produces rotation, supraspinatus stabilizes, and subscapularis contributes minimally.
• Increasing support load may be a targeted method to retrain axioscapular muscle stabilization functions.