Which muscle is primarily involved in external rotation of the shoulder?

The infraspinatus is primarily responsible for the external rotation of the shoulder. This muscle is one of the rotator cuff muscles located on the posterior aspect of the scapula. Its position allows it to effectively pull the head of the humerus backward and outward, which results in external rotation at the shoulder joint.

Understanding the roles of the rotator cuff is crucial for movements involving the shoulder, especially in Pilates where stability and strength are vital. The rotator cuff as a whole stabilizes the shoulder during activities that require arm movement, but the specific role of the infraspinatus in external rotation highlights its importance in maintaining proper shoulder mechanics and preventing injuries.

In contrast, the supraspinatus primarily assists with shoulder abduction, the subscapularis is mainly responsible for internal rotation, and teres major helps in internal rotation and adduction. Each of these muscles contributes to different shoulder movements, underscoring the specialized roles of the rotator cuff in shoulder stability and function.