The rectus abdominis is the paired superficial anterior abdominal muscle running vertically between the pubis and the lower ribs within the rectus sheath, interrupted at three or four tendinous intersections that create the visible six-pack appearance in lean individuals. It is the primary trunk flexor but contributes minimally to spinal stability compared to the deep transversus abdominis. Diastasis recti, a separation of the two rectus muscles at the linea alba, occurs commonly in pregnancy and is increasingly recognised in other populations.
| Origin | Pubic symphysis and pubic crest |
|---|---|
| Insertion | Xiphoid process and costal cartilages of ribs 5, 6, and 7 |
| Nerve Supply | Lower six intercostal nerves (T7 through T12) |
| Blood Supply | Superior and inferior epigastric arteries |
| Actions | Flexion of the lumbar spine; Compression of the abdominal contents; Assistance in forced expiration and childbirth |
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Its long vertical fibres and direct attachment between pelvis and ribs make it the most efficient trunk flexor but a poor spinal stabiliser, as it compresses the spine on the anterior side only without the circumferential tension of the transversus abdominis.
Diastasis recti, a widening of the linea alba exceeding 2 centimetres between the two rectus bellies, affects up to 60 percent of women at 6 weeks postpartum and produces functional trunk instability. Rectus abdominis avulsion from the pubic symphysis is a component of athletic pubalgia. The epigastric vessels run on the posterior surface of the rectus sheath and must be identified during laparoscopic trocar insertion to avoid injury.
The rectus abdominis is palpable in the midline between the xiphoid and pubic symphysis, its tendinous intersections creating the segmented appearance that is visible and palpable in lean individuals during a crunch movement.
Acute muscle tear from forceful trunk flexion or eccentric loading producing acute anterior abdominal pain, most commonly at the pubic attachment or at a tendinous intersection.
Linea alba separation exceeding 2 centimetres producing a midline abdominal gap with functional instability, assessed by finger width at the umbilical level and managed with specific deep abdominal rehabilitation.
