The sternocleidomastoid muscle, also referred to as SCM, is a muscle in the side of your neck that is the most superficial cervical muscles in the body as well as one of the largest. It’s responsible for the rotation of your head in the opposite direction and is also responsible for the bending of the neck. The muscle starts at the upper part of the sternum as well as the clavicle.
From there, it travels across the side of your neck where it connects to the temporal bone in the skull. When something goes wrong with this muscle is causes sternocleidomastoid pain that can limit your mobility and make everyday functions difficult or sometimes impossible.