The shoulder girdle
The shoulder girdle is a gliding joint (with slight rotation) where the clavicle articulates with the scapula, usually moving as a unit. The movements of the shoulder girdle include depression and elevation, upward rotation and downward rotation, as well as abduction and adduction.
The clavicles rotate around their own axes when the scapula moves. These help provide both stability and precision to scapular movements.
The anterior thorax muscles (front of the body) stabilise and depress the shoulder girdle. The only exception being the serratus anterior muscle. Most scapular movements are, therefore, caused by the posterior muscle and the serratus anterior. Several muscles have to act in combination for movements of the scapula.
The prime movers of shoulder elevation are the trapezius and levator scapulae, which act together to shrug the shoulders. Depression is largely the result of gravity pulling them back down. However, when depressing the shoulders against a resistance, the trapezius and serratus anterior, along with the aid of the latissimus dorsi muscle, come into play.
Forward movements (protraction or abduction) of the scapula are mainly due to serratus anterior involvement. This occurs in movements such as punching or pushing. Retraction or adduction of the scapula is caused by the trapezius and rhomboid muscles.