Reverse crunch: how to do it, on the floor or a bench, and what the studies measured

A reverse crunch is a crunch from the other end. Your head and shoulders stay on the floor, and your hips do the curling: with your knees bent, you roll your pelvis up off the floor so your knees come toward your chest, then lower it slowly. The move is small. If your legs swing, it stops being a crunch.

In the core workout, the reverse crunch on an incline bench is one of the "make it harder" options on the "curl forward" row. This page covers the setup, the mistakes, the bench version, what the studies measured, and the sets.

How to do a reverse crunch

1. Lie on your back with your arms flat at your sides (or your hands by your head) and your lower back pressed into the floor.
2. Lift your legs until your hips and knees are bent at about 90 degrees, knees over your hips. You can cross your ankles.
3. Curl your hips up: breathe out and roll your pelvis off the floor, bringing your knees toward your chest. Your lower back peels up a little.
4. Pause briefly at the top.
5. Lower slowly until your hips touch down and your knees are back over your hips. That's one rep.

The 2001 study's instructions are close: lower back pressed to the floor, hands beside the head or out to the sides, ankles crossed, knees at 90 degrees, and the hips rotating slightly with each contraction. They keep the lower back pressed down as you contract, where the cues here let it peel up a little.¹ The rest of the cues are practical, not study findings.

The common mistakes, and a fix for each

• Swinging the legs. Throwing the knees toward your face uses momentum. Pause at the top and lower for two or three seconds.
• Moving at the knees, not the hips. If your knees fold in and out but your hips stay on the floor, it's a leg tuck. The hips have to leave the floor.
• Rolling onto your neck. The curl ends with your lower back off the floor, not your shoulders. Keep it small.
• Crashing down. Lower your hips with control and stop when they touch.

What the reverse crunch trains

Every study here is a short lab measurement of muscle activity (electrical activity in the muscle, not growth). None trained anyone for weeks.

• Five ab exercises. In 25 healthy people, the reverse curl produced the most activity in the lower front abs (the lower rectus abdominis), and the reverse curl and the v-sit produced the most in the external obliques. For the upper front abs, a plain trunk curl, a trunk curl with a twist, the reverse curl and the v-sit were similar.²
• On a 30-degree incline. In 21 healthy men and women aged 23 to 43, a reverse crunch on a bench inclined 30 degrees, a hanging knee-up with arm straps and a wheeled ab device were the most effective of the exercises tested at activating the upper and lower front abs and the internal obliques. The incline reverse crunch was also among those with the most activity in the rectus femoris, a hip flexor on the front of the thigh.³
• Thirteen ab exercises. In 30 healthy women and men aged 20 to 45, the reverse crunch was third of 13 for oblique activity, 240% of a traditional crunch's, but only 109% of a crunch for the front abs, below the 25% margin the report used for "notably more effective".¹
• Less than a curl-up. In a pilot study of eight healthy adults, the reverse curl-up had significantly less activity in both the upper and lower front abs than the curl-up, and the two parts of the muscle showed no significant difference in any of the six exercises.⁴

Read together: these small studies disagree on the front abs. On a 30-degree incline the reverse crunch was among the most active exercises tested, and in the five-exercise study it led for the lower front abs; on the flat it was about level with a crunch in one study and below a curl-up in the smallest. All three that measured the obliques found it among the highest for at least one of the oblique muscles. More activity during a rep isn't proof of more benefit over weeks.

The reverse crunch on an incline bench

1. Set an adjustable bench at an incline and lie on it face up with your head at the high end.
2. Hold the bench behind your head with both hands.
3. Curl your hips up the slope, knees toward your chest, then lower slowly.

The 30-degree setup is the one the study above measured;³ the steps are practical. Start at a low angle and raise it only when 15 slow reps come easily.

Easier and harder versions

• Easier: feet on the floor and a smaller curl, or start with the hips only just lifting; the dead bug teaches keeping the lower back down first.
• Harder: a slower lowering (three seconds), the incline bench, or straighter legs.
• The next steps: the hanging knee raise and leg raise in the core workout, then toes-to-bar. V-ups curl both ends at once.

The easier and harder floor versions weren't compared in the studies above; they are practical.

Sets, reps and where they go

• Two or three sets of 10 to 15 slow reps, each stopped a rep or two before your form breaks, with about 60 seconds of rest.
• At the end of a session, after your main lifts, in the "curl forward" slot of the core workout, in place of the crunch.
• Progress one thing at a time. (Progressive overload covers the options.)

These numbers are practical, not from a study.

Common questions

Does the reverse crunch work the lower abs?

In one study it produced the most lower front-ab activity of five exercises.² In another, the upper and lower parts of the front abs showed no significant difference in any exercise,⁴ and the 2001 report suggested most people can't work them separately.¹ The front abs are one long muscle; the reverse crunch works it from the hip end.

Reverse crunch or regular crunch?

Both curl the trunk. The regular crunch moves your shoulders and the reverse crunch moves your hips. On the flat the studies above disagree for the front abs: level with a crunch in one, ahead for the lower front abs in another and below a curl-up in the smallest; on an incline the reverse crunch was among the most active exercises in the one study that tested it. Bicycle crunches add a turn to the regular crunch.

What if my back or neck hurts?

If you have pain, an injury or a medical condition, a doctor or a physical therapist should set the limits before you train; this page is general guidance for healthy adults.

If you'd rather have the week planned

Ab exercises are easy to list; fitting the right one into a week that already has squats, presses and pulls is the part a page can't do. Coaching is the version where your workouts live in Trainerize, built around the days and the equipment you actually have, and a weekly call looks at how the week went and sets the next one. Coaching for beginners explains how the first weeks work, and apply is the first step. Otherwise: at the end of your next session, do two slow sets of reverse crunches and write down the reps.