The TuneUp Program

Pectoralis major is the large muscle at the front of your chest. It attaches to the medial part of the clavicle, the sternum and the medial part of the lower ribs and inserts onto the upper arm where it forms the anterior wall of the axilla ( the front of the armpit).

It is primarily an adductor (it pulls the arm into the body) and a medial rotator of the arm. The upper fibres that attach to the clavicle will also pull the shoulder forward. If your shoulders are rounded, closing off your chest, you'll need to concentrate on the upper part of the muscle.