What muscle is primarily responsible for shoulder abduction?

The medial deltoid is the primary muscle responsible for shoulder abduction, which is the movement of the arm away from the body in the frontal plane. This muscle is situated on the outer part of the shoulder and has a significant role in lifting the arm to the side. While the anterior deltoid assists in shoulder abduction, particularly in the initial phase, and the posterior deltoid plays a role in the movement as well, it is the medial deltoid that executes the majority of the work during this specific motion.

In addition, while the full deltoid muscle, consisting of all three heads—anterior, medial, and posterior—does contribute to shoulder abduction overall, the medial deltoid is the most dominant and efficient muscle for this action. Understanding the specific functions of each part of the deltoid muscle can help in designing effective shoulder exercises and rehabilitation programs.