The posterior deltoid is one of the three muscle heads that make up the deltoid muscle, located on the outer shoulder. It is situated at the back of the shoulder and is primarily responsible for shoulder extension, external rotation, and horizontal abduction. This muscle plays a crucial role in various upper body movements, especially those involving pulling actions. Strengthening the posterior deltoid is important for maintaining shoulder stability and preventing injuries. Exercises like reverse flys and face pulls specifically target this muscle. A well-developed posterior deltoid contributes to a balanced shoulder appearance and enhances overall upper body strength.