What is the main function of the splenius muscles?

The main function of the splenius muscles is to facilitate the extension and rotation of the neck. These muscles are located in the posterior neck and are divided into two groups: the splenius capitis and the splenius cervicis. When they contract bilaterally, they help extend the head and neck backward. Unilaterally, when one side contracts, they assist in rotating the head and neck toward the side of activation. This dual capability of movement—both extension and rotation—is crucial for a wide range of activities involving head movement and is vital for maintaining proper posture and alignment of the cervical spine.

In this context, the other functions listed, such as stabilization of the lumbar spine, flexion of the trunk, and support for breathing, do not accurately represent the primary actions of the splenius muscles, which are specifically tailored for the movements of the cervical region.