Whenever exercisers lift the head and upper body from the mat, they lengthen the back of the neck and nod the head forward, without jamming the chin into the chest.
On the back of the neck, and frequently extending on to its lateral surfaces, is a shallow groove for the transverse atlantal ligament which retains the process in position.
Overdeveloped trapezius muscles -- a triangular shaped muscle that extends from the spine at the back of the neck to the shoulder -- give him huge neck.