The rectus abdominis is a long paired muscle located on either side of the midline and extending the length of the anterior abdominal wall. Both muscles are separated by linea alba in the midline.

The lateral margins of the rectus abdominis muscles create a surface marking known as the linea semilunaris. Along their course, the muscles are intersected by three or four transverse fibrous bands (tendinous intersections), which are easily visible on individuals with well-developed rectus abdominis muscles (or what is commonly known as a "six-pack").

Origin: pubic crest - from the pubic tubercle to the pectineal line, and pubic symphysis.

Insertion: costal cartilages of the 5th through 7th ribs, xiphoid process of the sternum.

Action: during bilateral contractions, the muscle participates in expiration and compresses abdominal contents, increasing the intra-abdominal pressure. During bilateral activation, it may flex the vertebral column. This muscle also tenses the abdominal wall.

Innervation: ventral rami of the lower six thoracic spinal nerves (T7 - T12), which are known as the intercostal nerves (T7 - T11) and subcostal nerve (T12).

Blood supply: mainly, the superior and inferior epigastric arteries, additionally, branches of the lower posterior intercostal arteries, subcostal artery, deep circumflex iliac artery.

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Rectus abdominis muscle