The trapezius muscle is complex and is involved in many functions, posturally it is a counterbalance against the forward flexion of the head, due to the head's slight anterior center of gravity in relation to it's axis. The trapezius elevates the pectoral girdle, rotates the scapula upwards, retracts the scapula, depresses the shoulders - it is involved in side flexion of the neck, axial rotation of the upper thoracic spine and extension.
For safety, when we are startled, we quickly shrug elevating our shoulders using our traps to safeguard our head by not allowing the occiput to be thrust backwards. This movement is natural and reflexive. Training on a neck machine we unconsciously elevate our shoulders as a protective mechanism restricting the normal range of motion of neck extension. To maximize neck strength hold the handle in front of the Pendulum 4 or 5 Way Neck machine's seat pad or hold on to the bottom of the seat pad which depresses the traps. Keeping the shoulders down during neck extension strength will grow quickly.......use good form to Get Strong.