Deltoid

The deltoid rises from the shoulder blade (scapula) and collarbone (clavicle), and attaches to the upper arm (at the top of the humerus). It is the main muscle for lifting the arm; it takes most of the mass of the bow during the early part of the draw. The rear (posterior) part has an important role in pulling the extended arm back; at full extension, this action helps keep the bow arm extended and the drawing arm pulled back.