Training guide
The ab crunch machine, also called the ab machine or abdominal crunch machine, is a seated crunch against a weight stack: you sit back against a pad with your feet hooked under rollers and curl your ribs down towards your hips. Designs differ (overhead handles with arm pads, a chest pad, or legs that rise as you curl), so set yours up by its placard, start light, and keep the movement in your spine, not your hips. It works your six-pack muscle hard, and your hip flexors more than a floor crunch does.
No study has compared it with floor or cable crunches, so this guide is honest about what the evidence shows: the machine built ab strength in the two small trials that used one, it won't take fat off your stomach, and the back and neck advice from our crunch guides applies.
It covers the steps on the 3D figure, set-up for each design, how heavy and how many, and who should choose something else.
Sit back against the pad, take the handles (or rest your arms or chest on the pads), breathe out and curl your ribs down towards your hips in a slow, steady pull. Pause, then let the weight take you back up over 2 to 3 seconds without the stack touching down. The American Council on Exercise (ACE) rates the machine crunch a beginner exercise.
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Set the seat so the machine's pivot sits level with the middle of your trunk, put the pads or handles where the placard shows, and start light. One maker's placard lines the pivot up with the middle of the trunk in just this way; no study has tested set-up, so this is coaching practice.
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In the one study of a seated ab crunch machine, 42 adults drew 84% of maximum from the six-pack muscle and 65% from the main hip flexor at the front of the thigh, against 104% and 27% in a ball crunch with an elastic band. A computer model also found the machine fitted small users badly. Keep the work in your spine, not your hips.
In 45 young adults, ab strength and endurance rose over 10 weeks on an ab crunch machine, as with incline sit-ups, though the summary gives no numbers. In 16 men doing unusual 4-minute intervals on a crunch machine, the crunch maximum rose 36% in 10 weeks. Two small trials, so read them as a reasonable sign, not proof.
Training one body part didn't take more fat off it across 13 studies of 1,158 people, 6 weeks of ab exercise changed no fat measure in 24 adults, and in the machine trial stomach skinfolds didn't fall.
2 to 3 sets of 8 to 12, stopping 2 or 3 reps short (the move page's dose), 2 or 3 days a week, with all your bending reps inside about 60 a session. Leave it out with osteoporosis or a past spinal fracture: the UK consensus advises avoiding loaded spinal bending.
From our move page (the set-up, the curl, the 2 to 3 second return and the cue to keep the legs relaxed), a maker's placard for the pivot, a gym equipment guide for the chest pad, and the hip flexor finding in the one machine study. Letting the stack down under control is editorial.
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The movement on the figure: Ab crunch machine
All are a seated crunch against a stack or plates, with your feet or shins hooked behind rollers. The commonest has overhead handles and arm pads; ACE's version is "Grasp the handles in both hands, and pull down on them to lean forward". Others use a chest pad, handles held with straight arms in front, or two motions at once, "the exerciser's upper body moving downward and the lower body moving upward". The placard on your machine is the best guide to its own set-up (our suggestion).
Mainly the rectus abdominis (the six-pack muscle down the front), with the obliques at your sides; makers list trunk flexion as the motion and the same muscles. Because you sit with your hips bent and your feet hooked, the hip flexors join in far more than in a lying crunch. The deepest layer, the transversus abdominis, isn't its target, as our crunch guide explains.
It lets you add load in small steps, which a floor crunch can't, and keeps you off the floor. But it fixes your seat and your path: a computer model found that small users "cannot be accommodated suitably". If you can't line the pivot up with the middle of your trunk, a cable crunch fits any size, as our cable crunch guide says.
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Nothing, by its move page. Controlled floor crunches help, and our crunch guide's ladder ends at this machine. People with osteoporosis or a past spinal fracture should leave it out.
Most ab machine numbers come from EMG (electromyography: electrodes measuring how hard a muscle works) over a few reps, which shows effort, not what a muscle will build.
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ACE: "Adjust the seat to a comfortable height and the weight to the appropriate level before beginning." One maker sets the seat to line the movement's pivot up with the middle of your trunk. Write your setting down, because machines differ (our suggestion).
Overhead handles: upper arms on the pads, elbows bent to about a right angle, as our move page shows. Chest pad: "Position the seat height so that the chest pad is aligned with your chest." Straight-arm handles: one maker's set-up is "Grasp handles, lean back while extending arms". Whichever you have, the arms only hold on.
Hook your feet or shins lightly behind the rollers and keep your legs relaxed. Pushing hard against the rollers turns the move into a hip bend, which the one machine study found the machine already invites.
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A maker's warning: "Never use dumbbells or other means to incrementally increase the weight resistance." Use the next pin instead.
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42 untrained workers aged 28 to 67 did 3 reps at their 10-rep maximum on a seated crunch machine and on a ball crunch against an elastic band. The six-pack muscle worked at 84% of maximum on the machine against 104% on the ball, and the rectus femoris (a hip flexor) at 65% against 27%; the obliques were similar. The authors put the hip flexor pull down to sitting with hips and knees bent near 90 degrees, and advised caution for people with lower back pain. It's one study, with one electrode site on the six-pack muscle.
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A 3D model with three virtual users predicted "unacceptable intervertebral joint loading" and a poor fit for the smallest, who also leaned on their hip flexors more. No people were measured, and the summary gives no forces, so treat it as a reason to keep the load moderate rather than a measured risk.
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We found no study comparing the seated machine with a floor crunch or a cable crunch, splitting upper and lower abs on a machine, or measuring spine load in a person using one. Everything here leans on that one EMG study, a model and other crunches.
Small EMG studies of the Ab Roller, Torso Track, Ab Rocker and similar home devices, in 14 to 46 young adults, found they matched or beat a floor crunch only when they copied the crunch and added resistance; several worked the abs less. Devices with high hip flexor activity "may be problematic for individuals with low back pathologies", one team wrote.
Small weights of 2 to 4 kg on a crunch mainly raised hip flexor activity in 9 women; in 13 people the abs worked hardest at 100% of their crunch maximum; and a synthesis of 87 studies lists added load among ways to raise ab work. Our reading: a load that makes 8 to 15 reps hard is the point, while a token load mostly adds hip flexor pull.
45 men and women aged 18 to 26 trained 3 times a week for 10 weeks on an ab crunch weight machine, a seated incline machine or incline sit-ups, and all improved ab strength and endurance; we read only the summary, which gives no numbers. 16 overweight men added 4 bouts of 4 minutes at 30 to 40% of maximum on a crunch machine to their running, 4 days a week, and their crunch maximum rose by 35 kg (36%) against 17% with running alone; that's an endurance-style protocol, not normal sets. Trunk training enlarged the six-pack muscle by about 2 square centimetres in 64 adults over 60.
A seated torso-twist machine worked the outer side muscle at 77% of maximum against 54% with an elastic band twist in 17 men, but 76% of them preferred the band. That's the only study we found of a rotary torso machine.
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Across 13 studies of 1,016 adults, machines and free weights built strength and muscle alike head to head, and an overview of 137 reviews found equipment type didn't consistently change results. None of those studies tested ab machines.
No study has compared them. The machine is easy to set and load in small steps; a cable fits any body size and makes it easier to keep your hips still, as our cable crunch guide explains; floor crunches cost nothing and keep the load light. All three build the same muscle.
Floor work is awkward for you, you want measurable load steps, or the cable station is busy (our suggestion).
You feel it in your hips or lower back, the pivot won't line up with your trunk, or bending flares your back: a cable crunch, a floor crunch or the no-bend moves below may suit you better.
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Our crunch guide's ladder, which ends at this machine: McGill curl-ups, 2 to 3 sets of 5 holds of 8 to 10 seconds (our 30-day ab challenge); the chest lift, 8 to 10 reps (its move page's dose); crunches, 2 sets of 10 to 15 for two weeks, then 2 or 3 sets of 12 to 20 (our sit-up and crunch guides); the long-arm crunch, 1 to 2 sets of 10 to 15 (our crunch and sit-up workout); the weighted crunch, 2 to 3 sets of 8 to 15, starting light (our editorial starting point); the kneeling cable crunch, 3 sets of 10 to 12 (our gym ab workout); the seated cable crunch, 2 to 3 sets of 10 to 15 (our cable machine guide); and the ab crunch machine, 2 to 3 sets of 8 to 12, stopping 2 or 3 reps short (the move page's dose). The machine and the cable crunch are alternatives, not steps above each other.
3D demoMcGill curl-upBeginner · No equipment
3D demoChest lift (Pilates curl-up)Beginner · No equipment
3D demoCrunchBeginner · No equipment
3D demoLong-arm crunchBeginner · No equipment
3D demoWeighted crunchIntermediate · Medicine ball
3D demoKneeling cable crunchIntermediate · A cable machine
3D demoSeated cable crunchIntermediate · A cable machine + A bench or box
3D demoAb crunch machineBeginner · Strength machineThe captain's chair knee raise and the hanging knee raise, 2 sets of 8 to 12 (our gym ab workout), and the decline bench crunch, 2 to 3 sets of 8 to 12 (our crunch guide's editorial starting point). The rotary torso machine has no 3D demo; the Pallof press below trains your trunk against turning.
2 sets of 10 to 12, stopping with 3 or 4 reps to spare, as our plans start every move. Pick a weight you think you could curl about 10 to 12 times.
2 to 3 sets of 8 to 12, stopping 2 or 3 reps short: the move page's dose, inside an expert review's "approximately 6-15 repetitions" with added load and NASM's 2 to 3 sets of 8 to 15 for moving ab exercises. Like the cable crunch, the last set can come within 0 to 2 once the movement is grooved (our editorial reading of our plans' rule for small moves). Going to failure added a trivial amount of muscle at most across 15 studies, and people misjudge the reps they have left by about one.
60 to 90 seconds between sets, as our cable crunch guide and plans suggest for small moves.
2 or 3 days a week counting all your ab work, with at least 48 hours between bending sessions and every bending rep (crunches, cable crunches, reverse crunches and this machine) inside about 60 a session: one expert review's untested suggestion, which our crunch guides keep to.
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When every set reaches 12, add the next pin and drop back to 8. Adding reps and adding load both worked in a trial of 43 trained people. There are no useful weight standards: maximums differ between machines and free weights, so compare yourself only on the same machine.
Jerking the weight brings in momentum and your hips. Choose a load you can curl smoothly, as the move page warns.
Your arms only hold on; curl your spine, as the move page cues.
If you sit back and fold at the hips, the hip flexors take over. Lighter weight, ribs to hips.
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Return slowly and keep the plates off the stack between reps.
Breathe out as you curl. Holding your breath drives blood pressure very high in hard efforts, as our breathing guide explains.
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They don't burn belly fat. Make the set harder instead, inside about 60 bending reps a session.
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Makers warn against it. Use the next pin.
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No study has measured spine load in a person on this machine. Sit-ups compressed the lower spine by more than 3,000 newtons in a model of 12 young men, partial curl-ups gave the most ab work for the spinal load of 12 exercises, and an expert review reports about 2,000 newtons for a basic crunch. A machine adds load, so more compression than a floor crunch is a fair assumption, but nobody has measured how much; the one model predicted high loads.
Pig spine segments herniated when bent up to 86,400 times under load in a lab. An expert review points out that living tissue adapts and sets are short, and calls harm to healthy spines "highly speculative"; it limits bending only for people with disc problems or back pain that's worse bending forward.
Usually your hips are doing the work. Lighten the load, relax your legs and curl from your ribs. With back pain, keep to our back pain guides' rule and stop anything that sends pain down a leg.
Aim for discomfort you'd call mild to moderate, no more than about 5 out of 10. It should settle within an hour or so, and your back should be no worse the next morning, as our back pain guides say. Pain, pins and needles or numbness spreading down a leg are the exception: stop, and see our sciatica guide.
No study has measured the neck on an ab machine. With your hands on the handles or pads, nothing pulls on your head (our reading). In curl-ups, restricting neck bending lowered neck-muscle activity from 32% to 22% of maximum and raised six-pack activity from 47% to 56% in 13 men, and breathing out slowly lowered neck activity in 12 adults. Lead with your chest, not your chin.
The UK osteoporosis consensus lists ab exercises in its programme "while avoiding loaded spinal flexion". The expert review limits bending for disc problems and back pain that's worse bending forward. In those cases, use the no-bend moves below.
With osteoporosis, a UK consensus advises modifying or avoiding repeated or end-range rounding of the spine: choose a dead bug, bird dog or plank instead.
Across 13 studies of 1,158 people, training one body part didn't take more fat off it. Six weeks of ab exercise on 5 days a week didn't shrink belly fat in 24 adults, 12 weeks of ab training added nothing to a diet in 40 women, and in the machine trial "local abdominal exercise alone is unsatisfactory for reducing stomach skinfolds or girths".
In 16 men, adding 57 minutes of crunch and twist machine work to running, 4 days a week, took about 0.7 kg more fat off the trunk than running alone. It's one small trial with an unusual protocol, and the larger evidence doesn't back it, as our get abs guide explains.
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Build ab strength and endurance. Seeing your abs depends on your overall body fat, which comes down with your overall activity and eating, not with one exercise. NASM: "No exercise can selectively burn fat from one area of the body."
These train the jobs the machine doesn't, and replace it with osteoporosis or a back that dislikes bending: cat-cow, 8 slow waves (its move page's dose), and a dead bug, 1 set of 6 each side, as a warm-up (our gym ab workout); a forearm plank, 1 hold of 20 to 30 seconds (our gym ab workout); side planks, 2 holds of 20 to 30 seconds each side (our full-body dumbbell workout B); bird dogs, 6 each side (our beginner core workout); the Pallof press, 2 sets of 10 each side (our gym ab workout); and suitcase carries, 2 walks of 20 to 30 m each side (our gym ab workout).
3D demoCat-cowBeginner · No equipment
3D demoDead bugBeginner · No equipment
3D demoForearm plankIntermediate · No equipment
3D demoSide plankIntermediate · No equipment
3D demoBird dogBeginner · No equipment
3D demoPallof pressIntermediate · A cable machine
3D demoSuitcase carryIntermediate · A dumbbell + A kettlebellOur gym ab workout uses the kneeling cable crunch; the ab crunch machine at the same sets and reps is a like-for-like swap. The crunch and sit-up, beginner core and advanced core workouts are the floor options, and the full-body machine workout fits the machine into a whole session.
A 25-minute gym ab workout you can add weight to: cable crunches, hanging knee raises, ab wheel rollouts, Pallof presses and suitcase carries.
25 minIntermediate7 movesA cable machine, Pull-up barA 15-minute ab workout with a crunch track and a sit-up track, about 60 bending reps at most, plus a side plank and bird dog to balance it.
15 minBeginner10 movesNo equipmentA 15-minute beginner core workout on the floor: dead bugs, bird dogs, knee planks, side planks and curl-ups.
15 minBeginner6 movesNo equipmentHard core training: ab wheel rollouts, hanging leg raises, L-sits, Copenhagen planks, plank walk-ups and dragon flags.
30 minAdvanced6 movesAn ab wheel, Pull-up barA 45-minute full-body gym workout on machines: leg press, chest press, machine row, leg curl, shoulder press and arms, with sets, reps and rest.
45 minBeginner14 movesCardio machine, A bandThe gym plan for beginners starts on machines; the 30-day ab challenge builds the floor steps.
A first gym plan for beginners: 3 days a week, starting on the machines, adding free weights and cardio, with what changes by week 12 and what comes next.
3 training days50 minBeginner4 days a weekA free 30-day ab challenge: four 12-minute core sessions a week, from dead bugs to hollow holds, with rest days and an honest word on belly fat.
4 training days12 minBeginnerLeave it out: the UK consensus advises that "Any exercise that causes the back to curve excessively especially with an added load should be modified or avoided". Train your trunk with Pallof presses, dead bugs, bird dogs and carries, and get individual advice from a physiotherapist when you start.
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Use the McGill curl-up, planks and the Pallof press instead, as our crunch guide suggests.
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Don't start loaded crunches new in pregnancy: the NHS says "It's not recommended to start a new vigorous activity in pregnancy" and to stop if you feel uncomfortable, too hot or unwell. Use standing or side-lying core work, as our crunch guide sets out.
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The NHS advises trying to avoid exercises such as sit-ups and planks to start with, and contacting the GP if the gap between your tummy muscles is still obvious 8 weeks after the birth. Curl-ups didn't widen the gap in one trial, but no study has tested loaded crunches.
With a stoma or after abdominal surgery, this is an advanced core exercise: work up through easier core levels first, and stop if you notice doming or bulging around your stoma or scar, as the move page says.
Crunches needn't be banned, but keep the load light (12 to 15 reps), breathe out on the effort, and leave out any move that makes the hernia bulge, as our hernia guide says.
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With controlled high blood pressure, the American Heart Association considers low- to moderate-intensity strength training with proper breathing safe. Breathe out as you lift, as our breathing guide advises.
Keep the load moderate: holding your breath in hard efforts drives blood pressure very high.
After heart surgery through the breastbone, or a heart or lung transplant, follow your surgeon's advice before pushing, pulling or lifting with your arms.
After breast cancer surgery or reconstruction, follow your surgical team's advice on when you can lift your arm above shoulder height, or push, pull or lift with it.
If you get chest pain or pressure, feel faint or dizzy, are unusually breathless, or your heart races or beats irregularly during exercise, as our plans advise. The American Heart Association says these need immediate medical evaluation.
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For chest pain that feels tight, heavy or squeezing, or spreads to your arms, neck, jaw or back; a sudden, extremely painful headache, especially while straining; someone who faints while exercising; or palpitations that don't go away, or come with chest pain, breathlessness or feeling faint. Don't drive yourself to A&E.
Ask for an urgent GP appointment or get help from NHS 111 for a headache that's triggered or made worse by coughing, sneezing, bending down or exercising.
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Call 999 or go to A&E: loss of feeling or numbness around the genitals or bottom, new trouble peeing or controlling your bladder or bowels, changes in genital sensation during sex or problems with erections or orgasm, or pain, tingling, weakness or numbness in both legs. These are signs of cauda equina syndrome, which needs treating in hospital urgently. Don't drive yourself.
See a GP if pain spreading down a leg hasn't improved after a few weeks of home treatment, is getting worse or stops your normal activities. Sciatica on both sides, or weakness or numbness in both legs that's severe or getting worse, is a 999 call or a trip to A&E.
See a GP if neck pain or stiffness hasn't gone after a few weeks, or comes with pins and needles or a cold arm, as our crunch guide says.
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A sudden sharp pain in your tummy wall during a set may be a strained muscle. Get help from NHS 111 or an urgent treatment centre if it's very painful or getting worse, badly swollen or bruised, or not getting better with self-care. Our abdominal strain guide covers recovery.
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See a GP if you think you have a hernia, a bulge or lump that may get bigger when you strain and smaller when you lie down. Get help from NHS 111 if you have a hernia and pain in or around it, a bloated tummy, you feel or are sick, you're vomiting blood or your vomit looks like coffee grounds, you're constipated, you have a high temperature or feel hot, cold or shivery, or you've suddenly become confused. Call 999 or go to A&E for a femoral hernia (a small lump at the top of your thigh, in your groin) with very bad tummy pain, sickness, being unable to fart or poo, a high temperature or sudden confusion.
The NHS lists lifting heavy weights among the causes of a femoral hernia. After an inguinal hernia repair, avoid heavy lifting or strenuous activity for at least 4 to 6 weeks.
See a GP about any leaking, which is common and treatable, or a lump in or around your vagina, or a feeling of heaviness or a bulge, as our pelvic floor guide says.
Speak to your GP first if you haven't exercised for some time or have medical conditions or concerns, as the NHS advises. Get advice before hard or straining work if your blood pressure is uncontrolled (140/90 or higher at a clinic, or 135/85 at home), or you have heart disease or chest pain when you're active, a pacemaker or defibrillator, diabetic eye disease, glaucoma, a hernia, recent eye or tummy surgery, or you're pregnant, as our breathing guide lists.
With a pacemaker or defibrillator, the American Heart Association asks you to check with your doctor before upper-body strength training, because repeated arm movements can damage or dislodge the leads.
Muscle soreness for a day or two after a new or harder session is common and fades. Sharp pain, or pain that builds during a set or lingers into the next day, isn't: swap to an easier version, and see a clinician if it persists, as our plans advise. The NHS says to stop exercising straight away if you feel any pain or become unwell, and to get help from 111 if symptoms worry you or don't go away.
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They build the muscle, not the view of it. Training a body part didn't take more fat off it across 13 studies, and the machine trial's skinfolds and girths didn't fall.
Ab strength rose on the machine in both small trials that used one, and it works the six-pack muscle hard. Its weak points are real (more hip flexor pull and a fixed fit), so it's an option, not the best ab exercise.
The harm case rests on pig spines bent up to 86,400 times under load; an expert review calls harm to healthy spines "highly speculative". Keep the load moderate, curl from your ribs, and change it if bending flares your back or you have osteoporosis.
Nobody has measured it. The one model predicted high spinal loads and the one EMG study more hip flexor pull.
Machines and free weights built strength and muscle alike head to head, and equipment type didn't consistently change results across 137 reviews.
Heavy loads raised ab activity in one study, but a load you can only move by folding at your hips trains your hip flexors. Choose the weight you can curl for 8 to 12 clean reps.
Set a light weight and the seat so the machine's pivot sits level with the middle of your trunk, then sit back with your feet hooked lightly under the rollers. Take the handles, breathe out and curl your ribs down towards your hips, pause, and come back up slowly without letting the stack touch down.
Mainly the six-pack muscle (rectus abdominis), with the obliques at your sides. It also works your hip flexors more than a floor crunch does: in the one study of the machine, the main hip flexor worked at 65% of its maximum against 27% in a ball crunch.
It's a reasonable way to load a crunch: ab strength rose on the machine in the two small trials that used one. It isn't a special ab builder and it brings in your hip flexors, so a cable or floor crunch is just as good if you can keep your hips still.
No study has compared them, and both load a crunch. The machine is easy to set up and load in small steps; the cable fits any body size and makes it easier to keep your hips still. Use whichever you can do with your hips still.
No study has compared them head to head. The machine lets you add weight once floor crunches are easy, but pulls in your hip flexors more; floor crunches cost nothing and keep the load light. Both build ab strength.
No. Training one part of the body doesn't take more fat off it, and in the ab machine trial stomach skinfolds didn't fall. Seeing your abs depends on your overall body fat, which comes down with your overall activity and eating.
Not for most healthy backs at sensible loads, though no study has measured the spine on one. Keep the weight moderate, curl from your ribs rather than folding at your hips, and keep bending reps to about 60 a session. Leave it out with osteoporosis, and swap to a dead bug or McGill curl-up if bending flares your back.
Usually because your hips are doing the work: sitting with your feet hooked brings in the hip flexors. Lighten the load, relax your legs and think ribs to hips. If your back still hurts, follow our back pain guide's rule and stop anything that sends pain down a leg.
A weight you could curl about 10 to 12 times: do 8 to 12 and stop 2 or 3 short, keeping 3 or 4 in reserve in your first two weeks. Stacks differ between machines, so compare yourself only with yourself on the same one.
2 to 3 sets of 8 to 12, resting 60 to 90 seconds, 2 or 3 days a week counting all your ab work. Add the next weight step when every set reaches 12.
Don't start loaded crunches new in pregnancy; use standing or side-lying core work, as our crunch guide sets out. After a birth, the NHS advises avoiding exercises such as sit-ups and planks to start with, and seeing a GP if the gap between your tummy muscles is still obvious at 8 weeks.
Home gadgets aren't the gym machine this guide covers. In small studies, they only matched or beat a floor crunch when they copied the crunch and added resistance, and some worked the abs less.
Exercise education, not a personal prescription, and clinical review of these guides is pending. Check with a GP before starting hard training if you have a heart condition, chest pain, dizziness or breathlessness when active, and stop for sharp or increasing pain. Health disclaimer.
