Crunch
Bodyweight
Primary muscles
Secondary muscles
Curling the ribs toward the pelvis flexes the spine, the main job of the rectus abdominis.
Form cues
- Lower back stays down
- Curl, do not pull on the neck
- Exhale at the top
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Primary SecondaryDrag · Pinch · Tap a muscle
What each muscle does in the crunch
| Muscle | Role | Action |
|---|---|---|
| Rectus abdominis | Primary | Flexes the trunk and braces the abdomen |
| External oblique | Secondary | Rotates the trunk to the opposite side and bends it to the same side; compresses the abdomen |
| Internal oblique | Secondary | Rotates and laterally flexes the trunk; compresses the abdomen |
Primary muscles are the prime movers; secondary muscles assist or stabilise. The balance shifts with grip, stance, range of motion and technique.