The two main functions of the cervical spine are:
1). Flex and extend the head
2). Flex and extend the cervical spine
The movement of flexion and extension occurs between the occiput (back of the head) and the atlas, producing the "yes" nod.
Flexion occurs in the range of 10 degrees and extension 25 degrees. This means the head can move through a 35 degree range of motion without neck participation.
The main flexors of the head in the 10 degree of flexion are the:
Rectus Capitis Anterior
The suboccipital muscle group extends the head and is comprised of eight muscles, one set of four on either side just below your skull.
This group around the atlas and axis are known to Anatomists as the, suboccipital triangle:
rectus capitus major
rectus capitus minor
Training the head musculature by flexing and extending the head.
In the photo below the athlete starts with their head ventral flexed. That is, the weight is pushing the athletes head parallel to the ground. Keeping the muscle of the neck firm the athlete then flexes the head about 10 degrees forward. They will feel a tremendous pull in the upper anterior portion of their neck.
To train the suboccipital muscles of the head the athlete starts by engageing their head musculature. In the below photo the athlete is beginning to dorsiflex his chin and is about 5 degrees from fully contracting the musculature just below his skull at the back of his head. It is about a 25 degree movement and only requires the neck muscles to stabilize the cervical spine, while the head muscles are engaged.
Training the neck musculature by flexing and extending the cervical spine.
Training the neck muscles on the same machine is quite different. The head is tilted back, the head stabilized and the neck, which has a greater range of motion than the head, does all the work.
Training the neck extensors requires a much greater range of motion
Side of neck
Pendulum has made their neck cam so the athlete does not need to know the above information. All the coach or the athlete needs to know is what pin hole to set the cam to perform the functions of the head and what pin hole is needed to train the the neck to Get Strong.