Machine Crunch: how to do it right
In short: The machine crunch is an isolation exercise for the rectus abdominis, loaded in the shortened position with peak tension at the end of the flexion.
How to do it, step by step
- 1Set the backrest and pads so your spine is centered on the machine's pivot axis.
- 2Curl the torso while hollowing the belly, as if bringing your lower ribs toward your pubis.
- 3Go for maximum shortening, back well rounded, without propelling yourself with your legs or arms.
- 4Squeeze hard for 1 second in the contracted position, you should feel your abs burn.
- 5Control the return slowly without fully relaxing at the end of the range.
- 6Keep a slow tempo, 2 seconds up, pause, 3 seconds on the way back.
The mistake to avoid
Don't do tiny reps. Curl your torso fully on every rep.
Other common mistakes
- Pulling with your arms or pushing on your legs to cheat: focus on curling the spine alone.
- Moving only at the hips without rounding your back: think about bringing the sternum toward the pelvis, not folding at the hip.
- Letting go all at once on the way back and losing tension: brake the eccentric to keep the abs under load.
- Skipping the final contraction: that's exactly where the tension is max, hold it for 1 second.
Muscles worked
- Main:
- Abs
The rectus abdominis, especially its upper portion above the navel, is the prime mover through spinal flexion. The obliques stabilize the trunk and prevent rotation. The transversus abdominis helps with deep bracing to lock the midsection.
What to replace it with
Same muscle, same part of the movement: these exercises do the same job.
- Cable Crunch ›
- Sit-Up Throw ›
- Cable Oblique Crunch ›
- Captain's Chair Knee Raise ›
- Weighted Dumbbell Russian Twist ›
Frequently asked questions
How do I do this exercise?
Set the backrest and pads so your spine is centered on the machine's pivot axis. Curl the torso while hollowing the belly, as if bringing your lower ribs toward your pubis, without pulling with your arms or pushing on your legs. Squeeze hard for 1 second at the bottom of the curl then brake the return.
How far down should I go?
Here the tension is max in the shortened position, when your torso is most curled. Go for maximum shortening, back well rounded, and hold 1 second at full contraction: that's where the work happens. Go for the full range you control, not the one you reach by wriggling.
I don't feel anything, is that normal?
On the machine crunch look for contraction quality, not load. Lower the weight and curl your back vertebra by vertebra with a real squeezed pause at the bottom: you should feel the rectus abdominis burn. If you feel nothing, it's often because you're pulling with your arms or folding at the hips instead of rounding your back.
How fast do I do the movement?
Curl over 2 seconds, hold the squeezed contraction for 1 second at the bottom, then brake the return over 3 seconds without fully relaxing. It's time under tension and the final pause that make the abs burn, not speed.
How do I breathe?
Exhale hard during the curl, exhaling helps you hollow the belly and contract the transversus. Briefly hold at full contraction to reinforce bracing, then inhale on the controlled return.