The rectus abdominis muscle (commonly known as "abs") is a paired muscle running vertically on each side of the athenterior wall of the human abdomen (and in some other animals). There are two parallel muscles, separated by a band of connective tissue called the linea alba (white line). It extends from the pubic symphysis/pubic crest inferiorly to the xiphisternum/xiphoid process and lower costal cartilages (5-7) superiorly.

It is contained in the Rectus sheath.

The rectus is crossed by three fibrous bands called the tendinous inscriptions. Colloqiual names for the appearance of a well-defined rectus abdominis include a "six pack" and "washboard abs"

Function

The rectus abdominis is a key postural muscle. It is responsible for flexing the lumbar spine, as when doing a 'sit-up'. The rectus abdominis can play a role in respiration in the event the patient is short of breath.

The Rectus abdominis is a long flat muscle, which extends along the whole length of the front of the abdomen, and is separated from its fellow of the opposite side by the linea alba.

It is much broader, but thinner, above than below, and arises by two tendons;

• the lateral or larger is attached to the crest of the pubis,
• the medial interlaces with its fellow of the opposite side, and is connected with the ligaments covering the front of the symphysis pubis.

The muscle is inserted by three portions of unequal size into the cartilages of the fifth, sixth, and seventh ribs.

The upper portion, attached principally to the cartilage of the fifth rib, usually has some fibers of insertion into the anterior extremity of the rib itself.