Neck
Neck contains several groups of muscles and the traction has two main functions: turning and tilting head. The two most important muscles are sternocleido mastoid that is front of neck and trapezius that is back and ends at brainpan. During tilting they are working. Wrestlers need strong muscles and bodybuilders have outstanding neck who did wrestling.
Overtraining neck muscles should be avoided because it is dangerous and shoulders seem narrower because of overdeveloped neck that is unbecoming to a bodybuilder.
Source: http://body.builder.hu