If you want to fully extend the cervical spine you must include protrusion, only protrusion takes Occ-C1 and C1-C2 to their end-range of extension. When the upper cervical segments are positioned in the extension portion of their total range the exercise targets the suboccipital muscles, that is, the rectus capitis posterior major and minor and obliquus capitis inferior and superior.

West Virginia Football

West Virginia Football Training the Suboccipital Muscles