PecsPectoralis Major

chest3 musclesMusculus pectoralis major

The pectoralis major is the broad fan of muscle across the front of your ribcage, and its job is to pull your upper arm in toward your chest. Every bench press, push-up and chest fly is built on that one action.

Pecs: its 3 muscles highlighted on an anatomical figure, from the front — Clavicular Head, Sternocostal Head and Abdominal Head.
Where the pecs sit, from the front.

The pecs cover the front of the ribcage in a fan. The wide end is anchored along the collarbone, down the breastbone, and across the upper ribs; all of those fibres converge and twist into a single flat tendon that attaches to the upper arm bone just below the shoulder. That layout is the whole story of the muscle: it is anchored to your torso at one end and to your arm at the other, so when it shortens, the arm moves and the torso does not.

The action is easiest to feel with no weight at all. Stand up, hold your arms straight out to the sides, and bring your hands together in front of you. That sweep across the body is horizontal adduction, and it is what the pecs are for. Pressing movements are the same action with a bar or a dumbbell in the way — the arms travel away from the chest and back toward the midline, and the pecs are what closes that gap. They also turn the upper arm inward, which is why a bench press feels different with your elbows tucked than with them flared.

The muscle arrives at the arm in three sets of fibres, running at three different angles: one from the collarbone pulling up and across, one from the breastbone pulling straight across, and one from the bottom pulling down and across. This is why incline, flat and decline pressing are not three names for the same exercise. The angle of the bench decides which set of fibres is best lined up with the direction the weight has to travel.

The pec major is regularly confused with the pectoralis minor, which is a smaller muscle underneath it. They do completely different jobs: the pec major moves your arm, and the pec minor moves your shoulder blade. Nothing you do for one is training the other.

Training notes

The pecs get more direct work than any other muscle in a typical gym and are still commonly trained through half their range. Pressing loads the muscle where it is strongest — near lockout — and gives it the least to do at the point where the arms are furthest apart. Flyes and cable crossovers cover the other end, where the fibres are long and the arm is travelling across the body rather than away from it. A chest session with no movement that brings the hands past the midline is leaving the muscle's defining action untrained.

The most common beginner complaint about pressing is feeling it in the front of the shoulder instead of the chest. Usually the bar is travelling too high up the torso and the elbows are flared to ninety degrees, which turns a chest press into a shoulder press on your back. Lowering the bar toward the lower half of the sternum and keeping the elbows nearer forty-five degrees from the body puts the working line back through the pecs.

The incline/flat/decline split is worth taking seriously and not worth obsessing over. All three angles train the whole muscle; they change the emphasis, not the target. Two pressing angles plus one movement that closes the arms across the body will cover the pecs more completely than five variations of flat bench.

Anatomy

Origin
  • Anterior surface of the medial half of the clavicle
  • Anterior surface of the sternum
  • Costal cartilages of the first to sixth ribs
  • Aponeurosis of the external oblique
Insertion
  • Crest of the greater tubercle of the humerus, on the lateral lip of the intertubercular sulcus
Actions
  • Adducts the arm, pulling it in toward the midline of the body
  • Horizontally adducts the arm across the front of the chest
  • Flexes the arm forward and upward from a hanging position
  • Internally rotates the humerus, turning the palm toward the body
Innervation
Lateral and medial pectoral nerves (C5–T1)

Parts of this muscle

Exercises

Antagonists

Synergists