The deltoid is opposed by the pectoralis major and the latissimus dorsi when the arm is moved away from the body to the side. The deltoid group functions to stabilize the shoulder during rotation, preventing dislocation and allowing safe carrying of heavy objects.
The deltoid muscle is comprised of three distinct fiber areas: the anterior fibers, located on the front of the shoulder; the lateral fibers, on top of the shoulder; and the posterior fibers, on the back of the shoulder. All of these fiber groups terminate at the same point on the humerus. The deltoid is named because of its triangular shape, similar to the Greek letter delta.