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The Core: An Overview

The abdominal muscles that flex, rotate, and — most importantly — brace and stabilize the trunk.

Before this: Fundamental Movement Terms

You will be able to

  • Name the four main abdominal muscles and what each does.
  • Explain the difference between a mover (rectus abdominis, obliques) and a stabilizer (transversus abdominis).
  • Describe why 'anti-movement' exercises are as important as sit-ups for a well-rounded core.
Simplified front view of the abdomen showing the segmented rectus abdominis running down the midline, the diagonal external oblique on each side, and the transversus abdominis wrapping around the waist beneath.
Core region — rectus abdominis, obliques, and transversus abdominis (simplified). A beginner-level schematic of the core's abdominal muscles: rectus abdominis, external oblique, and transversus abdominis.
Illustration: Anatomy Learning Platform (original) · CC0-1.0 (public domain dedication)

⚠ Safety note

Sharp abdominal pain or a visible bulge that worsens with straining needs medical evaluation, not exercise. A trainer coaches bracing technique; they do not diagnose abdominal conditions.

Four muscles, two jobs

The abdominal wall has four layered muscles:

  • Rectus abdominis — the 'six-pack' muscle that curls the trunk forward.
  • External oblique and internal oblique — layered, diagonal muscles that rotate and side-bend the

trunk (working in cross-body pairs).

  • Transversus abdominis — the deepest layer, wrapping around like a corset to brace the trunk.

Together they do two kinds of work: producing trunk movement (flexion, rotation) and resisting unwanted movement (bracing against an outside force).

Why 'anti-movement' matters

Real-world core demands are often about NOT moving — keeping the spine steady while you carry an uneven load, push a door, or catch your balance. That is why modern core training includes exercises like the plank, dead bug, and Pallof press alongside classic flexion work like crunches.

Bracing, not just sucking in

A proper brace — gently tightening the whole trunk, not just pulling the belly button in — uses the transversus abdominis and obliques together and is the foundation of safe lifting technique taught throughout this app.

Sources for this lesson

“The rectus abdominis, external oblique, internal oblique, and transversus abdominis flex, rotate, and compress the trunk.”

Anatomy and Physiology 2e — OpenStax, Rice University · Ch. 11.3 Axial Muscles of the Abdominal Wall, and Thorax

Peer-reviewed textbook · License: CC BY-NC-SA 4.0 · Last checked 2026-07-19

Take the quiz (3 questions)Explore the Core & Abdominal

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