What is the primary function of the sternocleidomastoid muscle?

The primary function of the sternocleidomastoid muscle is to assist in head rotation and flexion. This muscle, located on each side of the neck, is crucial for various movements of the head. When one side contracts, it allows for rotation of the head toward the opposite side, while simultaneous contraction of both sides leads to flexion of the neck, bringing the chin closer to the chest.

This muscle plays a significant role in the everyday movement of the head and neck, which is essential for numerous activities such as looking around and maintaining balance. Its importance is particularly noted in activities requiring head mobility and stabilization, reinforcing its primary function.