Crunches
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The basic spinal-flexion abdominal exercise placed in the "contracted" position of the Positions-of-Flexion abs chart; targets the rectus abdominus.
Detail
The crunch flexes the spine to work the rectus abdominus (with oblique involvement). Trunk flexion is produced by the rectus abdominis and the internal and external obliques. The abdominals' full ROM is 70 degrees, but smaller-range compression-style crunches are used for posture and spinal stabilization. Hip-flexor involvement should be reduced to a minimum; keeping the hip flexed and minimizing upward travel limits iliopsoas recruitment and lower-back stress. Performed with body weight (abs board/bench) or on machines (Keiser, Life Circuit, Body Masters).
Key facts
- Primary: Rectus Abdominus; Secondary: External Oblique, Internal Oblique.
- "Contracted" position of the Positions-of-Flexion abs chart.
- Minimize hip-flexor involvement to protect the lower back.
Connections
- rectus-abdominis — primary trunk flexor.
- external-oblique / internal-oblique — assist.
- abdominals — the abdominal group.
- iliopsoas-lordosis-situp — keep hip-flexor involvement minimal.
Educational content only — not medical advice. Always consult a qualified professional for individualized guidance, especially around injury, pregnancy, or medical conditions.