Rectus abdominis muscle

The rectus abdominis is a long, paired vertical muscle of the anterior abdominal wall extending from the thorax to the pelvis on either side of the linea alba. It is enclosed within the rectus sheath and is commonly referred to as the six-pack muscle due to its tendinous intersections.

Attachments

The rectus abdominis muscle originates from the pubic crest and pubic symphysis and inserts superiorly into the xiphoid process and the 5th to 7th costal cartilages.

Tendinous intersections

The muscle is divided into segments by three to four tendinous intersections that are firmly attached to the anterior wall of the rectus sheath. One is usually situated opposite the umbilicus, one at the extremity of the xiphoid process, and the third about midway between the xiphoid process and the umbilicus.

Rectus sheath

The rectus abdominis muscle is enclosed within the rectus sheath, a fibrous aponeurotic covering formed by the aponeuroses of the external oblique, internal oblique, and transversus abdominis muscles.

Innervation and vasculature

The rectus abdominis muscle is supplied by the thoracoabdominal nerves (T7T11) and the subcostal nerve (T12).

Its arterial supply is mainly from the superior epigastric artery, a branch of the internal thoracic artery, and the inferior epigastric artery, a branch of the external iliac artery.

Actions

Functionally, the rectus abdominis muscle is an important flexor of the trunk. Bilateral contraction produces flexion of the vertebral column, as seen when sitting up from a lying position. It also helps compress the abdominal viscera, thereby increasing intraabdominal pressure during actions such as coughing, defecation, vomiting, and childbirth. In addition, it stabilises the pelvis during walking and posture maintenance.