What is the primary action of the lower fibers of the trapezius?

The primary action of the lower fibers of the trapezius is scapula depression. The trapezius muscle is a large muscle that extends down the back of the neck and upper spine, connecting to the shoulders and upper arms. Its lower fibers are particularly effective in pulling the scapula downwards, which contributes to various movements, such as pressing down on the shoulders during certain activities.

By facilitating scapula depression, the lower trapezius fibers play a crucial role in positioning the shoulder girdle and are involved in actions such as extending the arm overhead or stabilizing the scapula during upper limb movements. This scapular movement is essential for maintaining proper posture and shoulder mechanics, especially during activities that require arm movement above the head. Understanding this action helps in both anatomical knowledge and functional application, particularly in exercise and rehabilitation contexts.