CoreBW
The classic trunk flexion exercise — a short-range curl of the upper spine off the floor, isolating the rectus abdominis without the hip flexor involvement of a full sit-up.
Demo: General S&C demo
Sets
3
Reps
15-20
Rest
30s
Contraindications
Neck strain — support the head lightly without pulling; avoid if disc-related low back pain worsens with flexion (consult McGill's guidance on flexion-intolerant backs).Setup
Lie on your back, knees bent, feet flat on the floor, hands lightly supporting the head or crossed on the chest.
Execution
- 1Exhale and curl the shoulders and upper back off the floor
- 2Keep the low back pressed into the floor throughout
- 3Curl only a few inches — this is a short-range flexion, not a sit-up
- 4Pause briefly at the top
- 5Lower with control back to the start
Key cues
- Curl, don't yank the neck
- Low back stays glued to the floor
- Exhale as you crunch up
- Short range, quality over height
Common faults
- Pulling on the neck with the hands instead of using the abs
- Using the hip flexors to sit all the way up (turning it into a sit-up)
- Holding breath instead of exhaling on the crunch
- Jerking up with momentum rather than a controlled curl
- Feet not staying flat, using them to assist the lift
Tweaks
- Add a slight pause at the top for more time under tension
- Progress to weighted crunches once form is solid
- Elevate the feet on a bench for a variation
Progressions
Muscles
Primary: Rectus Abdominis
Secondary: Obliques
Notes
FLEXION. The most basic trunk flexion movement; McGill cautions against high-volume crunching for flexion-intolerant backs, but it remains a canonical beginner movement.
Sources
Attribution: Classic S&C canon