The rectus abdominis is the paired, vertically oriented muscle running from the pubis to the lower ribs along the front of the abdomen, separated at the midline by the linea alba and divided into segments by three tendinous intersections that create the visible 'six-pack' appearance in lean individuals. While it is the most visually prominent abdominal muscle, it is primarily a spinal flexor rather than a core stability muscle, and over-reliance on it at the expense of the deeper transversus abdominis is a common pattern in people with chronic low back pain.
| Origin | Pubic crest and pubic symphysis |
|---|---|
| Insertion | Costal cartilages of ribs 5, 6, and 7; Xiphoid process of the sternum |
| Nerve Supply | Thoracoabdominal nerves (T7–T11); Subcostal nerve (T12) |
| Blood Supply | Superior epigastric artery; Inferior epigastric artery |
| Actions | Flexion of the lumbar spine (trunk curl); Posterior tilting of the pelvis; Compression of the abdominal viscera to assist forced expiration, defecation, and parturition |
|---|
It flexes the trunk toward the pelvis or the pelvis toward the trunk depending on which end is fixed, and plays a secondary role in managing intra-abdominal pressure during loaded exertion, functions that are complementary to but distinct from the stabilisation roles of the deeper core muscles.
Diastasis recti, a separation of the rectus abdominis at the linea alba, is common during and after pregnancy and can also occur in people who perform excessive trunk flexion exercises without adequate lateral core co-activation. Rectus abdominis strains are common in sports requiring rapid trunk flexion or rotation, such as gymnastics and rowing. The muscle is also a landmark for the inferior epigastric artery during laparoscopic surgery, where accidental vessel damage can cause significant haematoma.
The rectus abdominis is easily palpable as two vertical columns flanking the midline from just below the xiphoid to the pubic bone. The tendinous intersections can be felt as transverse firm ridges when the muscle is contracted during a partial sit-up.
Tearing of muscle fibres from sudden explosive trunk flexion or rotation, producing acute localised pain and tenderness over the muscle belly that worsens with any trunk movement, coughing, or sneezing.
Separation of the two bellies at the linea alba, most commonly occurring during pregnancy or from chronic intra-abdominal pressure, visible as a midline ridge during a partial sit-up and associated with reduced trunk control and lower back discomfort.
