Paired vertical straps down the front of the abdomen, cut across by fibrous bands, from the pubic bone to the xiphoid and lower costal cartilages
Rectus abdominis — the six-pack muscle.
Anatomy · Muscles
Rectus abdominis
The six-pack muscle
Abdomen · anterior wall, flexes the trunk
A long, flat, paired muscle that runs vertically down the front of the abdomen, one strap on each side of the midline, from the lower ribs to the pubic bone. Fibrous bands called tendinous intersections cut across it, and when body fat is low they show through the skin as the ridges of the six-pack. It bends the trunk forward and holds the abdominal contents in.
How to spot them
- ▸Two vertical straps either side of the midline, separated by the linea alba, from the pubis to the lower ribs and xiphoid process
- ▸Crossed by three (sometimes more) fibrous tendinous intersections, so it is divided into segments
- ▸Enclosed in the rectus sheath, formed from the aponeuroses of the three flat abdominal muscles
- ▸Supplied by the lower thoracic nerves T7 to T12
What to know
The ridged look of a lean stomach comes from these fixed fibrous bands, not from separate muscles
Rectus abdominis — the tendinous intersections, usually three per side, sometimes more.
Sheathed by the aponeuroses of the three flat muscles, the sheath having no back wall below the arcuate line
Rectus abdominis — the rectus sheath.
The two straps drift apart along the midline during pregnancy, leaving a bulge when the person sits up
Rectus abdominis — diastasis recti, a stretching of the linea alba.
A flap of it with its overlying skin, kept on the artery that runs within it, is used to rebuild a breast after mastectomy
Rectus abdominis — the TRAM flap, based on the superior epigastric vessels.
Two arteries from above and below, the superior and inferior epigastric, meet within it
Rectus abdominis — a link between the subclavian and external iliac systems.
Pulls the ribcage towards the pubis when a person does a sit-up or crunch
Rectus abdominis — flexion of the trunk.
Key ideas
- The intersections are firm attachments to the front of the sheath, so the muscle can shorten in segments; the number and position of them is fixed from birth and differs from person to person, which is why one person has a six-pack and another has an eight-pack or an uneven one.
- Visibility depends on the thickness of the fat layer over it, which is why the six-pack is a matter as much of low body fat as of training.
Quick-fire facts
- •Origin: the pubic crest and the pubic symphysis
- •Insertion: the xiphoid process and the costal cartilages of ribs 5 to 7
- •Action: flexes the trunk, compresses the abdominal contents and stabilises the pelvis in walking; depresses the ribs
- •Nerve supply: the thoracoabdominal nerves (T7 to T11) and the subcostal nerve (T12)
- •Blood supply: the superior epigastric artery (from the internal thoracic) and the inferior epigastric artery (from the external iliac), which anastomose within the muscle
- •Usually three tendinous intersections: at the xiphoid, the umbilicus and midway between, so with a fourth below the navel there may be eight segments
- •The linea alba, a tendinous line from the xiphoid to the pubic symphysis, lies between the two muscles
- •Pyramidalis, a small triangular muscle in front of its lower end, is absent in some people
- •Above the arcuate line the sheath passes in front of and behind it; below it all three aponeuroses pass in front
- •Diastasis recti is a widening of the gap along the linea alba, common in pregnancy and in infants
Drill it — 7 cards
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Sources
- TeachMeAnatomy — Rectus abdominis