What action is performed by the supraspinatus muscle?

• A. Adducts shoulder
• B. Extends shoulder
• C. Flexes shoulder
• D. Rotates shoulder medially

Answer: (B)

The supraspinatus muscle primarily initiates abduction of the shoulder joint, particularly during the first 15 degrees of motion. It plays a crucial role in stabilizing the shoulder by holding the head of the humerus in the glenoid cavity. While this question's answer indicates extension of the shoulder, which is not the main action of the supraspinatus, it's important to recognize that this muscle is located at the top of the shoulder and works closely with other muscles like the deltoid to facilitate movement.

Abduction—moving the arm away from the body—is critical for many overhead activities and is not accurately represented in the provided answer choices. The supraspinatus assists in lifting the arm, especially during early stages of abduction, while the deltoid muscle takes over for movement at larger angles.

Understanding the precise role of the supraspinatus clarifies its importance in the broader context of shoulder mechanics and movement patterns.