The deltoid muscles, or delts, are the groups of muscles capping the shoulder. Each deltoid consists of three distinct muscle groups or heads: the anterior, posterior and lateral deltoids. These muscles are responsible for working the shoulder joint, moving the arm away from the body in all directions and providing strength and stability to the shoulder.
Delts are shaped like triangles curving over each shoulder. In fact, the name is derived from delta, the Greek word for a triangle. Each of the deltoid heads is anchored to a different point on the torso, with the anterior connected to the collarbone and the posterior and lateral fixed to the different portions of the shoulder blade. All three come together at the upper portion of the humerus and create a distinct V shape on the upper arm.
Each of these deltoid heads is responsible for lifting the arm in one specific direction. Anterior deltoids give the arm forward motion, posterior deltoids pull the arm backward, and lateral deltoids a move the arm to the side. Working in tandem, the delts give the arm the ability to stretch up and out from the body at any angle. With the help of other upper-body muscle groups, deltoids add to the shoulder’s range of motion, allowing it to shrug, drop and rotate.
Deltoids also are responsible for holding the shoulder together and minimizing damage. When one is carrying a heavy load, the delts bear that weight and prevent the load from pulling the humerus out of its socket. In cases where objects need to be held away from the body, such as with a sloshing bucket, the deltoids are able to raise these loads laterally.
Developed deltoids give the upper body a broader, more imposing silhouette, and exercises focused on the deltoids are popular among bodybuilders and other athletes. Bodybuilders must keep in mind the function of each portion of the delts for a balanced physique. Focusing on a single range of motion will develop only a third of the deltoid muscles. Exercises working each of the deltoid heads must be selected to develop the entire muscle group.
Workouts targeting the delts most often involve weightlifting. Deltoid workouts commonly include variations on military presses, lateral raises and front raises. Any motion of the shoulder will, however, work a portion of the deltoids, and expensive gym equipment is not required. Simple push-ups or chin-ups will give the shoulders an excellent workout.