Which action is performed by the infraspinatus muscle?

The infraspinatus muscle is primarily responsible for externally rotating the humerus and assisting in shoulder extension. This muscle is one of the four rotator cuff muscles and plays a crucial role in stabilizing the shoulder joint while allowing for movement.

When it contracts, it pulls the greater tubercle of the humerus backward, facilitating external rotation, which is essential for various overhead movements and throwing actions. Additionally, the infraspinatus can assist with shoulder extension when the arm is already in a flexed position.

Understanding the role of the infraspinatus helps clarify its importance in maintaining shoulder stability and function during various activities, especially those involving arm movement above the head.