What is the collective function of all deltoid muscles?

The deltoid muscles are primarily responsible for the abduction of the humerus, which is the movement of the arm away from the body in a lateral direction. The deltoid muscle is divided into three parts: the anterior, lateral, and posterior fibers. While the anterior part can assist in flexion and the posterior part can assist in extension of the shoulder, it is the lateral fibers that are most directly involved in abduction, particularly when raising the arm from the side to above shoulder level.

This abduction movement is essential for various functional activities such as reaching, lifting, and throwing. Therefore, recognizing the deltoids as the key muscles in facilitating this specific movement highlights their importance in shoulder mobility and function.