Abduction of shoulder is initiated by

Abduction of shoulder - abduction and adduction take place at right angles to the plane of flexion and extension , i. e., approximately midway between the sagittal and coronal planes. In abduction , the arm moves anterolaterally away from the trunk. This movement is in the same plane as that of the body of the scapula. Muscles bringing about movements at the shoulder joint - (i)Both Supraspinatus and Deltoid muscles initiate abduction and are involved throughout the range of abduction from 0 - 90 digrees. (ii)Serratus anterior 90 - 180 digrees (iii) Upper and lower fibres of trapezius 90 - 180 digrees. Ref : B D Chaurasia's Human Anatomy , seventh edition , volume 1, pg. no., 149.