Crunch: how to do it right.
The crunch is the simplest flexion exercise for the abs, and precisely for that reason the most butchered: it's not a sit-up cut in half, it's a short, precise curl where the ribs move down toward the pelvis. Ten centimeters of movement done with the rectus abdominis beats a hundred done with the neck.
Starting position
- Lie on your back, knees bent, feet flat on the floor hip-width apart (NOT locked under a support).
- Hands lightly touching your temples or crossed on your chest: never laced behind the neck to act as a winch.
- Lower back in contact with the floor, chin a fist's width from your chest.
Proper form
- Exhale and "curl" your upper back: head first (without pulling it), then shoulders, then the shoulder blades lift off the floor.
- Think of bringing your ribs toward your pelvis, not your head toward your knees.
- Stop once your shoulder blades are off the floor and your abs are at peak contraction: that's 10-15 centimeters, no more.
- Squeeze for a second at the top, with your lower back staying glued to the floor.
- Uncurl slowly, one vertebra at a time, without dropping down "dead weight".
- Start the next rep without bouncing: every rep originates from the abs, not from momentum.
When to inhale, when to exhale
Exhale COMPLETELY as you curl up (the air leaving helps the rectus abdominis shorten), inhale as you uncurl. In the crunch, breathing is half the exercise.
Mistakes to avoid
Hands dragging the head stress the cervical spine and trick you into thinking the abs are working. Hands should just brush the temples; if your neck gets tired, imagine holding an orange under your chin.
Past the point where your shoulder blades lift off, the work shifts to the hip flexors: that's a sit-up, a different exercise (with different demands on the lower back). The crunch ends where the abs' range ends.
Dropping down and bouncing back up uses your back as a spring and hands half the reps over to momentum. The slow descent IS the exercise, just as much as the ascent.
Fifty rapid-fire crunches train very little. Fifteen slow ones, with a full exhale and a squeeze at the top, change how the exercise feels from the first set on.
DAWT tip. Once the floor crunch gets easy, don't just keep adding reps forever: add load (a plate on your chest) or move to the cable crunch, where progression is measurable like in any other exercise. Even abs follow progressive overload.
Variations and alternatives
Quick answers
How many crunches a day for sculpted abs?
No number of crunches "sculpts" abs on its own: definition depends on body fat, which comes down to diet and overall training. Crunches build the muscle that will show once everything else is in place.
Are crunches bad for your back?
With the lower back on the floor and a short range of motion, most healthy backs tolerate crunches well. It becomes a problem when it turns into a yanked-out sit-up with feet locked down.
Crunch or plank, which is better?
They do different jobs: the crunch trains flexion (the abs shortening), the plank trains anti-extension (the abs holding steady). A complete core needs both, plus rotational work.
Related exercises
How much should you load on this exercise?
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