At the deepest layer of the necks cervical extensors is the cervical multifidus and the semispinalis cervicis.  These muscles provide neck support and prevent forward head posture.  The multifidus is a powerful small muscle that takes pressure off the cervical discs and is a segmental stabilizer.  The semispinalis cervicis is an extender.  Anatomically, they are able to control vertebral movements in concert with the deep flexors of the cervical spine.

Population studies show athletes with small deep extensors, especially women, incur more cervical pain and more neck pain related issues from sports.  Muscle pain has an immediate effect of altering the activation of both deep and superficial function during a cervical extension exercise or during activity and must be attended to.

The small powerful multifidus and semispinalis are extremely important to keep strong.  The multifidus increases its size quickly when there's a sudden contraction of the shoulder muscles, regardless of force or the direction of the force.  This muscular group having a unique spinal protective mechanism is a solid reason to always include neck strengthening as a regular part of an exercise program.

Neck Extension on the Pendulum 5- Way Head and Neck Machine