The shoulder muscles play a large role in how we perform tasks and activities in daily life. We'll discuss the function and anatomy.

Each shoulder has three separate muscles that, together, compose the deltoid muscle parts: Anterior deltoids. When you move your thumb inward, you use your anterior deltoids.

The rotator cuff is made up of four muscles that hold your shoulder in place. It helps you perform all the movements of your upper arm and shoulder.

The trapezius, traps, trapezoid muscle is in the upper back and helps the neck, shoulders, and arms move. Learn more about the causes and treatment of trapezius pain.