The muscles near delts are the pectoralis major (PECS) and the latissimus dorsi (LATS). The pectoralis major is a large, fan-shaped muscle located in the chest that connects the sternum, ribs, and clavicle to the humerus. The latissimus dorsi is a large, flat muscle located in the back that connects the spine to the humerus. Both of these muscles are important for shoulder movement and stability.