What is the role of the posterior deltoid muscle?

The posterior deltoid muscle plays a crucial role in the movement and stabilization of the shoulder joint. It is primarily responsible for the extension of the humerus, which involves moving the arm backward away from the front of the body. This action is essential in various movements, such as reaching behind you or performing certain exercises like bent-over rows or rear delt flies.

In addition to extension, the posterior deltoid facilitates horizontal abduction, where the arm is moved away from the midline of the body in a horizontal plane. This dual function of extending and horizontally abducting the humerus allows for a wider range of arm movements, particularly in activities that require pulling or reaching backward.

Understanding the function of the posterior deltoid is important for designing exercise programs and rehabilitation protocols, as it helps to improve shoulder strength, range of motion, and overall upper body stability.