Reverse Crunches

What the reverse crunch actually trains

A reverse crunch is a floor based abdominal exercise in which you draw your knees towards your chest and curl the pelvis off the floor, then lower under control.

The rectus abdominis does the work, specifically through posterior pelvic tilt, which is the part of the movement where the hips leave the ground. The external and internal oblique assist and keep the movement square. The hip flexors, meaning psoas major, iliacus and rectus femoris, bring the knees up in the first half.

The distinction between those two halves is the entire exercise. Bringing your knees towards your chest is a hip flexor movement. Curling your pelvis towards your ribs is an abdominal movement. Most people do the first and stop, then wonder why they feel it in the front of their hips rather than their stomach.

There is nothing wrong with the hip flexors being involved. They are working muscles and they deserve training. But if the reason you chose this exercise is the abdominal wall, then the pelvic curl is not an optional flourish at the top; it is the repetition.

The reverse crunch earns its place mostly through accessibility. It needs no equipment, it can be done anywhere, and it puts far less compressive load through the spine than a heavy weighted sit-up. That makes it a reasonable default for a lot of people.

Its weakness is equally clear. Bodyweight is the only load, and once you can do fifteen clean repetitions there is nowhere obvious to go. Abdominals respond to progressive loading like every other muscle, so it stops doing much once it is easy. Weighting it, or moving to a decline bench or a cable, is what keeps it useful.

Setting up and executing

Lie on your back with the knees bent to roughly ninety degrees and the feet off the floor.

Place your arms flat beside you, or hold the legs of a bench behind your head if you need something to anchor against.

Press the lower back gently into the floor and brace the abdominal wall without holding your breath.

Draw the knees towards the chest, then keep going by curling the pelvis so the hips lift off the floor. That second part is the repetition.

Pause for a beat at the top of the curl.

Lower the hips back down slowly, over about three seconds, keeping the lower back in contact with the floor the whole way. Stop before the feet touch and begin the next repetition.

The mistakes that cost you the most

Swinging the legs is the fault that empties the exercise. If you throw the knees up and let them fall, momentum is doing the work and the abdominal wall barely participates. A three second lowering phase solves it immediately, and it will also make sets of ten feel like plenty.

No pelvic curl is the second and more common problem. If the hips never leave the floor, this is a knee tuck. Escamilla and colleagues found that rectus abdominis involvement varies substantially across abdominal exercises and with how they are performed, and here the difference between a curl and a tuck is exactly that kind of variation.

The lower back arching on the way down tells you the range is currently too long for your control. When the pelvis tips forward and the lumbar spine lifts off the floor, the hip flexors and lumbar extensors have taken over. Shorten the range, keep the back down, and extend it as control improves.

Chasing repetition counts is the programming version of the same error. Sets of fifty are not a stronger stimulus than sets of twelve with a slow eccentric and a dumbbell between the feet.

And expecting it to burn belly fat is worth stating plainly once. It will not. No abdominal exercise removes fat from the abdomen.

Sets, reps and rest by goal

Moderate repetitions, slow lowering, and a plan for adding load.

For muscle gain, four sets of ten to fifteen with a minute rest. For strength, four sets of eight to twelve with ninety seconds. In a fat loss phase, three sets of fifteen to twenty with forty five seconds.

The tempo is the first progression. Take three seconds to lower the hips and pause for a beat at the top, and a set of ten becomes genuinely difficult without changing anything else.

The second progression is load. Hold a light dumbbell between the feet, use a decline bench, or attach a cable at the ankles. Schoenfeld and Grgic reviewed range of motion and muscle development and found that training through fuller ranges generally favours growth, which supports the decline version once you have the control for it.

Schoenfeld and colleagues found a dose response between weekly hard sets and hypertrophy, and this movement is cheap enough that eight to twelve abdominal sets a week is easy to accumulate.

Refalo and colleagues found stopping a rep or two short of failure produces comparable growth to going to failure, which matters here because the failing rep is usually the one where the lower back arches.

Where it fits in your split

At the end of a session, on whichever days suit you, two or three times a week.

On push, pull and legs it can close any day. On a two day upper split it works as a finisher. On a bro split it is a good main flexion movement on abs day. On an upper and lower split it fits the lower session after the main lifts. On a bodyweight programme it goes anywhere, since it needs nothing.

Abdominals recover quickly, so frequency is your friend. Three sets three times a week beats nine sets in one heroic session.

What it should not be is the whole of your abdominal training. A complete programme wants flexion, which this covers, plus something rotational and something anti-extension. Adding a loaded twist and a plank or a carry alongside it takes very little time.

If you already do hanging knee raises, this is largely the same movement done lying down. Pick whichever you can progress more easily and keep that one.

Variations worth knowing

The weighted reverse crunch, with a light dumbbell held between the feet, is the simplest way to keep progressing once bodyweight becomes easy.

The decline reverse crunch performed on a decline bench lengthens the range and increases the difficulty considerably, which is the natural next step.

The hanging knee raise is the standing up version, harder overall and limited by grip rather than abdominal strength.

The lying leg raise keeps the legs straighter, which loads the hip flexors more heavily and demands more control at the bottom.

The cable reverse crunch attaches resistance at the feet and is the easiest version to load in small increments, which makes it the best long term progression.

And the dead bug is the anti-extension counterpart, holding the trunk still while the limbs move, which trains the same muscles without spinal flexion.

What the evidence says

Escamilla and colleagues analysed a range of commercial and common abdominal exercises and found substantial differences in rectus abdominis and oblique involvement between them, which supports being selective rather than assuming any abdominal movement is equivalent.

In their comparison of traditional and nontraditional abdominal exercises, Escamilla and colleagues again found that technique and movement pattern drive the differences, which is the case for insisting on the pelvic curl rather than a knee tuck.

Escamilla and colleagues also compared Swiss ball and traditional abdominal exercises and found that greater whole body control demands increased abdominal involvement, which is why slowing the movement down changes the exercise so much.

Schoenfeld and Grgic reviewed range of motion and muscle development and found fuller ranges generally favour growth, supporting the decline variation once your control allows it.

Vigotsky and colleagues cautioned that electromyography amplitude does not directly predict hypertrophy, which is worth keeping in mind before ranking abdominal exercises by activation charts alone.

Schoenfeld and colleagues found a dose response between weekly hard sets and muscle growth, which applies to the abdominal wall as it does everywhere else.

Refalo and colleagues found stopping short of failure produces comparable hypertrophy to training to failure, supporting ending the set while the lower back stays down.

Common questions

Reverse crunch or normal crunch?

They emphasise different ends of the same muscle. A crunch curls the ribs towards the pelvis; a reverse crunch curls the pelvis towards the ribs. Neither is dramatically better, and doing both is unnecessary. Pick the one you can perform cleanly and load progressively.

Why do I feel it in my hip flexors?

Because you are lifting your knees rather than curling your pelvis. The hip flexors do the first half of the movement by design. Keep going until the hips leave the floor and the abdominal part appears.

How do I make it harder?

Slow the lowering to three seconds first. Then hold a light dumbbell between your feet, move to a decline bench, or attach a cable at your ankles. Adding repetitions past twenty is the least effective option.

Will this flatten my stomach?

It will build the muscle underneath. Whether you can see it depends on body fat, and no abdominal exercise burns fat from the area it works. Train the muscle here and handle visibility through your diet.

Is it better than a hanging knee raise?

Not better, just easier to access and easier to control. The hanging version is harder but is often limited by grip. If you have a bar and good grip, hang. If you want something you can do anywhere and load with a dumbbell, this is fine.