Shoulder Rotation Affects Trapezius Muscle Activity During Shoulder Horizontal Abduction

Area of Science:

• Biomechanics
• Exercise Physiology
• Rehabilitation Science

Background:

• Prone shoulder horizontal abduction effectively targets the lower trapezius but poses challenges for patients in early rehabilitation.
• Modifying exercise positioning may enhance muscle activation and patient tolerance.

Purpose of the Study:

• To investigate the impact of varying shoulder rotation on trapezius muscle activation and scapular tilt during horizontal abduction.
• To assess the effect of shoulder rotation on acromiohumeral distance in a seated position.

Main Methods:

• Fifteen healthy males performed seated shoulder horizontal abduction in internal rotation, neutral, and external rotation.
• Electromyography measured trapezius muscle activity; an inclinometer assessed scapular tilt.
• Real-time ultrasonography measured acromiohumeral distance pre-exercise.

Main Results:

• External rotation significantly increased lower and middle trapezius muscle activity (p<0.001).
• Scapular anterior tilt decreased, and acromiohumeral distance increased with external rotation (p<0.05).

Conclusions:

• Seated shoulder horizontal abduction with external rotation enhances middle and lower trapezius activation.
• This modified exercise may provide a safer and more effective approach for shoulder rehabilitation.