Shoulder Girdle Muscles
The shoulder girdle consists of the scapula (shoulder blade) and the clavicle (collar bone). The muscles which produce movement of the shoulder girdle are the trapezius muscle, levator scapulae, rhomboids, serratus anterior, pectoralis minor, sternocleidomastoid and the subclavius muscle.
The Sternocleidomastoid muscle is the big thick muscle in the neck and is easily seen at the front of the neck when rotating the head the other way. It allows the neck to bend forwards and sideways.
There are two rhomboid muscles - Rhomboid major is larger and positioned below rhomboid minor. Both muscles work together to retract the scapula (bring the shoulder blades together) and rotate the scapula.
The Trapezius is part of the group of muscles which elevate and retract the shoulder girdle. It is divided into parts; upper, middle and lower.
Shrugging the shoulders (scapula elevation) requires the use of levator scapulae and Trapezius. Fixation of the scapula by other muscles, allows the levator scapulae muscles to work together to aid cervical extension, or independently to laterally flex (side bend) the neck towards the side of the working muscle.