The shoulder is a complicated joint of the human body because it is responsible for so many planes of motion (front, rear, up, down, and across). It is a “3 headed” muscle. Meaning it has 3 major muscles that control the movements. The front deltoid is called the anterior deltoid, the middle is the medial deltoid, and the rear is the posterior deltoid. In order to work the shoulder well, you must work all three heads to prevent any imbalances. Front raises will work the anterior deltoid, side raises work the medial deltoid, and rear raises target the rear deltoid (as well as the back). Compound movements like a seated dumbbell press work mostly the anterior and medial deltoid.