Abdominal HeadAbdominal Head of Pectoralis Major

chestPars abdominalis musculi pectoralis majoris

The abdominal head is the lowest part of the pectoralis major, arising from the sheet of tissue over the abs rather than from bone. It pulls the arm down and in, which is what a dip and a decline press ask for.

Abdominal Head highlighted on an anatomical figure, from the front.
Where it sits, from the front.

This is a small set of fibres at the bottom edge of the chest. Unlike the rest of the muscle it does not come off bone at all — it arises from the tough sheet of connective tissue that covers the upper abdomen, then runs upward and outward to join the same tendon as the other two parts.

Because it starts below the arm and finishes above it, the abdominal head pulls the arm down and in toward the body. A dip is the clearest example: the arm travels from beside the shoulder down toward the hip while the torso leans forward over it. A decline press is the same direction with the body rotated. Straight-arm pulldowns and high-to-low cable crossovers also work here.

Two honest caveats. First, this part of the muscle is small and is not consistently present in everyone — anatomical references treat it as a variable structure rather than a guaranteed one. Second, "lower chest" as most people use the phrase means the lower border of the whole pectoralis major, which is mostly the bottom fibres of the sternocostal head. Both are trained by the same movements, so the distinction matters more for reading an anatomy chart than for writing a program.

Training notes

Dips are the most efficient thing here and the most commonly done wrong for this purpose. Staying upright turns a dip into a triceps exercise; leaning the torso forward over the hands and letting the elbows travel slightly out is what puts the line of pull through the lower chest.

High-to-low cable crossovers cover the same direction with far less load on the shoulder and let the hands cross past each other at the bottom, which finishes the adduction that a dip stops short of.

The lower chest is not a way to change the shape of the chest's bottom edge — that line is set by where the muscle attaches and by the tissue over it, neither of which training moves. What training does is make the muscle underneath bigger, which is worth doing on its own terms.

Anatomy

Origin
  • Aponeurosis of the external oblique, over the upper part of the rectus sheath
Insertion
  • Crest of the greater tubercle of the humerus, attaching highest of the three sets of fibres
Actions
  • Adducts the arm downward and inward, as in a dip or a decline press
  • Draws the shoulder girdle down by pulling on the humerus
  • Assists internal rotation of the humerus
Innervation
Medial pectoral nerve (C8–T1)

Exercises

Antagonists

Synergists