Rectus Abdominis
The rectus abdominis is a paired muscle running vertically on the anterior abdominal wall. It is the 'six-pack' muscle and is the primary flexor of the trunk, also playing a role in breathing and intra-abdominal pressure.
Origin, Insertion, Action, Innervation
OOrigin
Pubic crest and pubic symphysis
IInsertion
Xiphoid process and costal cartilages of ribs 5-7
AAction
- • Flexion of the trunk (against gravity)
- • Compression of abdominal contents
- • Depression of the ribs (assists forced expiration)
- • Stabilization of the pelvis during walking
NInnervation
Intercostal nerves (T7-T12)
Blood Supply
Superior and inferior epigastric arteries
Clinical Relevance
Rectus diastasis (separation of the two rectus muscles at the linea alba) can occur after pregnancy or with obesity. The muscle is divided by tendinous intersections that create the 'six-pack' appearance. It is vulnerable in abdominal surgery.
Palpation
Palpate on the anterior abdominal wall. Have the patient perform a sit-up or raise their head from supine to feel the muscle contract. The tendinous intersections can be felt.
Study Tips
- ✓Runs from 'pubis to ribs' (pubic symphysis to costal cartilages)
- ✓Tendinous intersections = 'six-pack' appearance
- ✓Enclosed in rectus sheath formed by other abdominal muscles
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Common questions about the rectus abdominis
The six-pack appearance is created by tendinous intersections that divide the rectus abdominis into distinct segments. These intersections are horizontal fibrous bands that adhere to the anterior rectus sheath.
The linea alba is a fibrous midline structure that separates the left and right rectus abdominis muscles. It extends from the xiphoid process to the pubic symphysis and is formed by the fusion of abdominal muscle aponeuroses.
Rectus diastasis is a separation of the left and right rectus abdominis muscles at the linea alba. It commonly occurs during pregnancy or with significant weight gain and may cause a bulge in the midline when straining.
The rectus abdominis is innervated by the lower intercostal nerves (T7-T12), which also provide sensory innervation to the overlying skin.