Pecs (Pectoralis muscle group) connect the front walls of the chest with the bones of the upper arm and shoulder. You have two Pec muscles on each side of the sternum (breastbone): a pectoralis major and a pectoralis minor.
Pecs help you move your arms down (adduction), rotate your arm forward, and side to side (lateral). It assist your arms when they’re raised (as in climbing). Pecs assist in deep breathing, too, tugging on the ribs to help lungs expand.
Developed pecs are most recognized in males, because breast tissue typically hides the pectoralis muscles in females.