muscles that move the upper arm. STUDY. PLAY. pectoralis major. Primary Function: prime mover of arm flexion; rotates arm medially; adducts arm against resistance; pulls ribcage upward with scapula and arm fixed to help in climbing, throwing, pushing, throwing, and force inspiration. Origin: clavicle, sternum, cartilage of ribs 1-6, and aponeurosis of external oblique muscle.