Bicep
One of the main upper arm muscles, the bicep is unusual in covering two different joints. It starts from two points on the outer tip of the shoulder blade*. From there, it travels along the main upper arm bone (the humerus) and is fixed to the forearm near the elbow, specifically attaching to the radius (the forearm bone on the thumb side). It is one of the main muscles responsible for bending the arm at the elbow. In archery, the drawing arm bicep comes into use in the early part of the draw, keeping the string close to the bow arm through the draw. Ideally, it should largely relax as the drawing elbow comes around behind the string. Generally, a heavily loaded bicep at full daw is a sign of poor form, likely to make a clean loose very difficult.
*The coracoid process and the upper part of the glenoid cavity, which the humerus fits into
Exercises: Try chins