Lie prone on bench with head extended off of end and folded towel and weight plate(s) on floor. With both hands, place plate(s) on back of head with towel placed in between for comfort.
Move head up by hyperextending neck up as high as possible. Return by bending neck down until chin touches upper chest. Repeat.
Balance weight on back of head with both hands throughout movement. Weight plate(s) can be tilted slightly to higher point on head to keep resistance slightly more consistent throughout movement. Tilt weight forward slightly at top and back slightly at bottom. Also see same movement with body lying perpendicular to bench.