The pectoralis major muscle is a large muscle in the upper chest, fanning across the chest from the shoulder to the breastbone. The two pectoralis major muscles, commonly referred to as the 'pecs,' are the muscles that create the bulk of the chest. A developed pectoralis major is most evident in males, as the breasts of a female typically hide the pectoral muscles. A second pectoral muscle, the pectoralis minor, lies beneath the pectoralis major. The pectorals are predominantly used to control the movement of the arm, with the contractions of the pectoralis major pulling on the humerus to create lateral, vertical, or rotational motion. The pectorals also play a part in deep inhalation, pulling the ribcage to create room for the lungs to expand. Six separate sets of muscle fiber have been identified within the pectoralis major muscle, allowing portions of the muscle to be moved independently by the nervous system. Injuries to the pectoralis major can occur during weightlifting, as well as other bodybuilding exercises that place excessive strain on the shoulders and chest.