What action is associated with the sternocostal head of the pectoralis major?

The sternocostal head of the pectoralis major is primarily responsible for shoulder extension from a flexed position. This muscle plays a significant role in movements that involve the upper arm and shoulder, particularly when the arm is already flexed at the shoulder joint. When the arm is elevated, the sternocostal head helps bring it back down and across the body, which is what occurs during shoulder extension from a flexed state.

Considering the actions of the pectoralis major as a whole, the muscle's contributions to flexion, adduction, and rotation of the shoulder are important, but the specific focus of the sternocostal head in facilitating extension from a previously flexed position highlights its distinct functional role. This action is significant, especially in activities that require movement of the arm backward or towards the body after it has been raised.