Which action is NOT associated with the deltoid muscle?

The deltoid muscle is a large, triangular muscle located on the outer aspect of the shoulder. It is primarily responsible for a variety of arm movements due to its specific anatomical positioning and orientation across the shoulder joint.

Abduction is one of the key functions of the deltoid; it facilitates the lifting of the arm away from the body. Additionally, the deltoid contributes to both flexion and extension of the shoulder joint. The anterior part of the deltoid helps in flexion (bringing the arm forward), while the posterior part assists in extension (moving the arm backward).

Depression, however, is not an action associated with the deltoid muscle. Depression refers to the movement of the scapula or shoulder blade downwards, which is primarily facilitated by other muscles, such as the trapezius and the serratus anterior. Since the deltoid does not perform this action, it makes depression the correct answer regarding what is not associated with the deltoid's primary functions.