Abdominals

The front and sides of your core. More a corset than a six-pack: these muscles flex and rotate the trunk, but their bigger job is bracing the spine and transmitting force between your upper and lower body.

This muscle in 3D

Drag to rotate · scroll to zoom — see the shape, origin and insertion of the abdominals. 3D model via Sketchfab (CC-BY).

Anatomy

Muscles: Rectus abdominis, external & internal obliques, transversus abdominis

Origin: Rectus abdominis: pubic crest. Obliques: lower ribs and iliac crest. Transversus: inner ribs, thoracolumbar fascia, iliac crest.

Insertion: Rectus: 5th–7th ribs and sternum. Obliques: linea alba and iliac crest. Transversus: linea alba (wraps horizontally).

Actions:

• Trunk flexion (rectus)
• Trunk rotation & side-bending (obliques)
• Compress abdomen / brace the spine (transversus abdominis)
• Resist extension and rotation (anti-movement, the core's real job)

How the muscle works

Concentrically they curl the ribcage toward the pelvis; more often they work isometrically, stiffening the trunk so the limbs have a stable base to push from. Intra-abdominal pressure from transversus protects the lumbar spine under load.

Fibre-type bias: Mixed, with a postural (type I) lean in transversus and deep fibres — built for endurance and bracing.

Functional role: Force transfer and spinal protection in almost every lift, sprint, throw and change of direction.

Common problems

• Diastasis recti (separation of the rectus)
• Poor bracing → low-back overload
• Over-flexion strain from endless crunches

Training & stretching

Anti-extension (planks, dead-bugs), anti-rotation (Pallof press) and loaded carries build the bracing role; flexion work (crunches, leg raises) trains the rectus.

Gentle spinal extension (cobra/upward dog) lengthens the rectus abdominis.

Fix or train this

• Lower Back Pain
• Build Muscle (Plateau)