Rectus abdominis muscle

At a glance

English

Rectus abdominis muscle

Latin (TA2)

Musculus rectus abdominis

System

Muscle

Region

Trunk

Side

Paired, left and right

About the rectus abdominis muscle

The rectus abdominis is a long, strap-like muscle running the full height of the anterior abdominal wall, one on each side of the midline. The two are separated by the linea alba, a fibrous seam, and the curved lateral edge of each is marked on the surface by the linea semilunaris. Each muscle is wider and thinner above, narrower and thicker below.

It arises below from the pubic crest and symphysis, and runs up to attach to the xiphoid process and the costal cartilages of the fifth to seventh ribs. Fibrous bands called tendinous intersections cross it and fuse with the front of its sheath, dividing it into a stack of short bellies. In lean people these bellies bulge between the bands when the muscle tightens, producing the familiar segmented outline.

The muscle lies inside the rectus sheath, a tough envelope built from the aponeuroses of the flat abdominal muscles beside it. The inferior epigastric artery climbs behind its lower part and enters the sheath at about the arcuate line; the superior epigastric artery, a continuation of the internal thoracic, comes down to meet it from above, and segmental vessels join from the side. Branches of the lower thoracic spinal nerves pierce the sheath to reach it.

Its chief action is to bend the lumbar spine forward, drawing the ribcage and pelvis towards each other, as in a sit-up or a posterior pelvic tilt. It also stiffens the abdominal wall, raises pressure inside the abdomen during lifting, coughing and straining, and helps push air out in forced expiration. Strains of the muscle are common in sport, and tearing of an epigastric vessel can cause a rectus sheath haematoma, a painful mass that is more frequent in people taking anticoagulants and usually settles without surgery over weeks to months.

Attachments, action and supply

Origin

Pubic crest and symphysis pubis.

Insertion

Xiphoid process and the costal cartilages of the fifth to seventh ribs.

Action

Flexes the lumbar spine, bringing the ribcage and pelvis together; tenses the abdominal wall, raises intra-abdominal pressure and assists forced expiration.

Nerve supply

Thoracoabdominal nerves (T7 to T11) and the subcostal nerve (T12).

Blood supply

Superior and inferior epigastric arteries, with segmental branches of the lower posterior intercostal arteries.