Pectoralis major muscle.
The pectoralis major muscle arises from the anterior surface of the sternal half of the clavicle and the cartilage of the top ribs. It inserts into major tubercle of the humerus. It is a very powerful muscle and helps with rotation and extension of the shoulder joint, and adduction of the humerus. Lifting the arms helps passively when we inhale deeply. The muscle is so flexible that many movements can be performed without the muscle being hindered by other fibres that are not directly involved in the angle of strength development.
Sports requiring optimal strength in the arms depend on this highly important muscle.