What is a key shoulder action of the teres major muscle?

• A. Flexes elbow
• B. Rotates shoulder laterally
• C. Medially rotates shoulder
• D. Adducts shoulder

Answer: (C)

The teres major muscle is primarily known for its role in shoulder movement, specifically in medially rotating the shoulder joint. This action involves turning the arm inward toward the body, which is crucial for various movements such as reaching behind the back or performing certain lifting tasks.

In addition to medial rotation, the teres major also assists in adduction of the shoulder, meaning it helps pull the arm closer to the body. However, its most defining action is that of medial rotation, making this the key shoulder action associated with the muscle. Understanding the teres major's function is important for recognizing how it contributes to overall shoulder mechanics, particularly in movements that require a degree of internal rotation.

The other options describe actions that are either performed by other muscles or are not primary functions of the teres major. For example, flexion of the elbow is a function of the biceps brachii, while lateral rotation is a key action of muscles like the infraspinatus. Adduction does occur but is secondary to medial rotation when considering the teres major's primary role.