The rectus abdominis muscle is a paired muscle running vertically on each side of the anterior wall of the human abdomen (and in some other animals). There are two parallel muscles, separated by a midline 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 usually crossed by three fibrous bands linked by the tendinous inscriptions. While the “sixpack” is by far the most common configuration of the muscle bellies of the rectus, there exist rare anatomic variations which result in the appearance of eight (“eightpack”), ten, or—even rarer—asymmetrically arranged segments. All these variations are functionally equivalent.
The rectus abdominis is an important postural muscle. It is responsible for flexing the lumbar spine, as when doing a “crunch”. The rectus abdominis assists with breathing and plays an important role in respiration in the event the patient is short of breath. It also helps in keeping the internal organs intact and in creating intra-abdominal pressure, such as when exercising or lifting heavy weights, during forceful defecation or parturition.
The rectus abdominis has several sources of arterial blood supply. In reconstructive surgery terms, it is a Mathes and Nahai Type III muscle with 2 dominant pedicles. First, the inferior epigastric artery and vein (or veins) run superiorly on the posterior surface of the rectus abdominis, enter the rectus fascia at the arcuate line, and serve the lower part of the muscle. Second, the superior epigastric artery, a terminal branch of the internal thoracic artery, supplies blood to the upper portion. Finally, numerous small segmental contributions come from the lower 6 intercostal arteries as well.
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. 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.
Some fibers are occasionally connected with the costoxiphoid ligaments, and the side of the xiphoid process.
An abdominal muscle strain, also called a pulled abdominal muscle, is an injury to one of the muscles of the abdominal wall. A muscle strain occurs when the muscle is stretched too far. When this occurs the muscle fibers are torn. Most commonly, a strain causes microscopic tears within the muscle, but occassionally, in severe injuries, the muscle can rupture from its attachment.
The Rectus Abdominis is similar in most vertebrates. The most obvious difference between animal and human abdominal musculature is that in animals, there are a different number of tendinous intersections.
levator ani (iliococcygeus, pubococcygeus, puborectalis) · coccygeus
fascia/pelvic fascia visceral (Rectovaginal fascia, Rectoprostatic fascia) · parietal (Obturator fascia/Tendinous arch, Piriformis fascia)
floor/diaphragm: Superior fascia of pelvic diaphragm (Pubovesical ligament, Puboprostatic ligament) · Inferior fascia of pelvic diaphragm


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