Abdominal Crunch Machine: The Ultimate Guide
The abdominal crunch machine is a seated ab exercise on a weight stack. Set the seat so the machine's pivot sits level with your midsection, hold the handles or pads lightly and curl your ribs toward your hips, then uncurl slowly. It trains the rectus abdominis and obliques. Most lifters do 3 sets of 10 to 15 reps.
- 1Start. Seat set so the pivot sits level with your midsection. Back on the pad, feet under the rollers, hands on the handles beside your head.
- 2Crunch. Curl your ribs toward your hips so your chest drops toward your thighs. Your hands stay beside your head; your abs move the arm.
Watch 2 video demonstrations
How to use the ab crunch machine
- Find the pivot mark on the frame, a dot, arrow or sticker next to the axle the moving arm swings on. Set the seat so it sits level with your midsection, between your lower ribs and your navel.
- Sit back against the pad with your feet under the rollers or on the foot bar, and set the pin.
- Hold the handles or pads lightly. Your arms only keep you attached to the machine.
- Breathe out and curl your ribs toward your hips, rounding your back as far as the machine lets you. Pause for a second.
- Uncurl over 2 to 3 seconds and stop just before the plates touch, then start the next rep.
Which ab crunch machine do you have?
All four train the same motion, trunk flexion, and the same muscles. What changes is how you hold on and how much your hips join in. Cybex tells users of its front-handle machine to push the handles "by bending forward from the trunk while keeping arms fully extended". On clamshell machines such as the Nautilus Inspiration, the legs and arms move together, so the hips bend as well as the spine. In one study a plain crunch drew less rectus femoris (hip flexor) activity than any of five V-up style exercises that also moved the legs (Schoffstall 2010).
How to set up the ab crunch machine
The pivot is the setting that matters. The moving arm swings around an axle, and your spine should bend around the same line. Many brands mark it: Hammer Strength with a red indicator, Nautilus with a highlighted axis on the frame. Set the seat so that mark sits level with your midsection, between your lower ribs and your navel.
Too low, near your hips, and the machine turns you at the hips like a sit-up. You feel it in your hip flexors and your lower back peels off the pad. Too high, near your chest, and only your upper back bends while the pads slide on your shoulders.
Not every machine has a seat to set. Some fit you with the feet instead: on the Cybex Eagle you set the foot bar for a slight knee bend so your back stays on the pad, and the Hammer Strength Select has two foot supports for different heights. Whatever adjusts, set it so the pivot lines up with your midsection and your hips stay on the seat.
The pivot is too low, or you are bending at the hips instead of the spine. Raise the seat a notch, keep your hips down and think ribs to hips, not chest to knees.
How much weight should you use on the ab crunch machine?
On Gravitus, the median man lifts 110 lb (50 kg) for 10 reps on the abdominal crunch machine, and the median woman 60 lb (27.5 kg).
- Most lift
- 80 to 150 lb
- Top 10% lift
- 185 lb or more
- Starting out
- under 80 lb
- Most lift
- 45 to 85 lb
- Top 10% lift
- 110 lb or more
- Starting out
- under 45 lb
- Most lift
- 37.5 to 67.5 kg
- Top 10% lift
- 85 kg or more
- Starting out
- under 37.5 kg
- Most lift
- 20 to 37.5 kg
- Top 10% lift
- 50 kg or more
- Starting out
- under 20 kg
Abdominal crunch machine muscles worked
Ab crunch machine vs cable crunch vs floor crunch
| Attribute | Ab crunch machine | Cable crunch | Floor crunch |
|---|---|---|---|
| Resistance | Weight stack, fixed path | Cable stack, you set the angle | Bodyweight |
| Setup | Seat or foot bar to line up the pivot | Rope, pulley height, kneeling spot | None |
| Adding load | Move the pin | Move the pin | Hold a plate, or add reps |
| Best for | Beginners, heavy sets with the hips held still | Any gym with a cable stack | Anywhere, warm-ups, high reps |
No study has compared these three for ab growth. Across 13 studies, machines and free weights built muscle equally (Haugen 2023), so pick the one you can set up well and keep adding weight to.
Sets, reps and progression
Stop each set 0 to 2 reps short of failure. Sets taken close to failure build muscle across a wide range of reps (Schoenfeld 2021), so a range of 10 to 15 works as long as the last reps are hard.
Add reps first. When every set reaches 15 clean reps, move the pin up one plate and drop back to 10. Keep the seat setting the same from week to week, or the new number means nothing.
Common mistakes
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Pulling with your armsOn handle machines the lats and arms take over. Hold the handles loosely and keep your elbows still.
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Hinging at the hipsYour torso tips forward in one piece and the hip flexors do the work. Curl your spine, ribs toward hips.
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Pivot out of lineA seat set for the last person puts the axle at your hips or chest. Check the pivot mark every time you sit down.
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Leading with your headTucking your chin hard strains your neck without moving the arm. Keep your head in line with your back.
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Dropping the stackThe lowering half is part of the rep. Uncurl over 2 to 3 seconds and stop before the plates touch.
Ab crunch machine variations
Questions people ask
What muscles does the ab crunch machine work?
The rectus abdominis, with the obliques helping. The hip flexors hold your pelvis still and work harder on machines where your legs move too.
How should I set the seat height on the ab crunch machine?
Set it so the pivot mark on the frame sits level with your midsection, between your lower ribs and your navel. If you feel your hip flexors, raise the seat a notch. If only your upper back bends, lower it.
Are ab crunch machines effective?
Yes, for training the abs with load you can track. Machines built muscle as well as free weights across 13 studies (Haugen 2023). They will not show your abs on their own; that takes lower body fat.
Does the abdominal crunch machine burn belly fat?
No. Six weeks of ab exercises did not change belly fat in one trial (Vispute 2011), and 12 weeks of ab training added to a diet cut no more belly fat than the diet alone (Kordi 2015). Fat loss comes from eating less than you burn. The machine builds the muscle underneath.
Is the ab crunch machine better than cable crunches?
Neither has been shown to build more muscle. The machine holds your hips still and takes seconds to set up. The cable crunch lets you choose the angle and works on any cable stack. Use the one you can keep adding weight to.
How much weight should I use on the ab crunch machine?
For 10 reps, the median on Gravitus is 110 lb (50 kg) for men and 60 lb (27.5 kg) for women. The strongest quarter lifts 150 lb (67.5 kg) and 85 lb (37.5 kg) or more.
Log every set and see your percentile on every lift, abdominal crunch machine included.
Get GravitusRelated exercises
- Schoffstall et al. 2010. J Strength Cond Res 24(12):3422-3426.
- Vispute et al. 2011. J Strength Cond Res 25(9):2559-2564.
- Kordi et al. 2015. J Manipulative Physiol Ther 38(3):203-209.
- Haugen et al. 2023. BMC Sports Sci Med Rehabil 15:103.
- Schoenfeld et al. 2021. Sports 9(2):32.
- SportsArt S931 Abdominal Crunch owner's manual, 2013.
- Cybex Eagle 11090 Abdominal owner's manual.
- Hammer Strength Select Abdominal Crunch, Life Fitness.
- Nautilus Inspiration Abdominal Crunch, Core Health & Fitness.