How to Do Frog Crunches for Sculpted Upper and Lower Abs

illustration of a person doing a frog crunch
The frog crunch is a challenging ab exercise that hones in on the deep layers of your core, including your transverse abdominis and obliques.
Image Credit: LIVESTRONG.com Creative

Standing side crunches, bicycle crunches, you know the deal. You've crunched your way through countless crunch and sit-up variations. But there's one more — and completely awesome — take on the traditional crunch that we bet you haven't tried: the frog crunch.

Named after the motion that a frog makes when swimming in the water, frog crunches are one of the most challenging core exercises you can do.

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  • ​​What is a frog crunch?​​ It's a crunch variation that involves lifting your upper back off the floor (like in a traditional crunch) while bringing your knees toward your chest — with your legs in a diamond shape. Then, you extend your legs out in front of you.
  • Are frog crunches effective?​​ Unlike standard crunches, where your lower body remains still, this variation get your whole body moving, which requires a lot of stability work from your core, says certified personal trainer Nedra Lopez Matosov, CPT. And when you combine a full-body movement with a stability component, you really fire up your midsection.
  • What muscles do frog crunches work?​ They target your core muscles, including your transverse abdominis (the deepest layer of your abs), rectus abdominis (the "six-pack" muscles) and your internal and external obliques (the side abs). In addition, they activate your inner thighs (more on this later).

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How to Do Frog Crunches With Perfect Form

  1. Lie on your back with your knees bent and feet planted on the floor.
  2. Open your legs, allowing your knees to fall to the sides, and press the soles of your feet together. Your legs should make a diamond shape.
  3. Place your hands by your ears and open your elbows to the sides. Never clasp your hands behind your head, which may encourage you to pull on (and strain) your neck.
  4. Crunch up, using your core to lift your shoulders and legs off the ground, and try to meet your elbows to your knees.
  5. Then extend your legs, keeping the soles of your feet as close together as possible, while lowering your upper body to the floor.

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3 Frog Crunch Benefits

1. They Target Your Entire Core

As long as you move slowly and with control, you will feel your upper abs, lower abs and obliques (which must work to stabilize you), Lopez Matosov says. For an intense ab burn, focus on lifting your upper back up as much as you can, she adds.

2. They Help Improve Posture and Balance

The key to improving your posture involves building a strong core, so this ab exercise — which targets your trunk — can be an important part of a posture-strengthening program, she says.

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The longer you can hold your legs out in the frog crunch exercise, the stronger your stabilizing core muscles will become, she says.

3. They Strengthen Your Inner Thighs

"Because you are externally rotating your hips with your feet together, you are automatically activating your adductors," Lopez Matosov says. And if you consciously press your feet together, you can intensify the inner-thigh engagement, she says.

4 Frog Crunch Tips

1. Use Your Abs

This is an ab exercise, so you want to focus on initiating the movement from your core and upper back and not from your neck.

"I cue my clients to lift from their upper back, bringing their shoulder blades off the floor, so they can see their bellybutton at the top of the crunch," she says.

2. Maintain a Neutral Back

To keep your lower abs and obliques active throughout the exercise, press your lower back into the floor to prevent arching, Lopez Matosov says.

If you find your lower back lifting off the floor during frog crunches, try reducing your range of motion and keep your legs closer to your body with each rep, she suggests.

As you build core strength over time, you'll be able to extend your legs with control (and without lifting your back) to get the most out of the exercise without back pain or injury.

3. Breathe Through the Exercise

Exhale as you crunch up and inhale as you lower and extend your legs, Lopez Matosov says.

"So many people hold their breath when exercising," she says. But breathing is especially important when engaging and strengthening your core.

4. Tuck Your Pelvis

If you don't engage your abs properly, your hips flexors will take over, Lopez Matosov says. Not only will this reduce the exercise's effectiveness for your core, but it'll also tax and tighten your hip flexors.

"As long as you tuck your pelvis, your hip flexors will take a back seat to your abs," she says.

Tip

If you can't get onto the floor or have limited mobility, you can always do the exercise on your bed, she says. This works best with a firm mattress.

3 Modifications to Make the Move Easier

Frog crunches are an advanced ab exercise, so you might need to first build up your strength before leaping in. Here's how to modify the move in the meantime.

1. Keep Your Legs Close

If you're experiencing back pain or discomfort during the exercise, avoid extending your legs fully. "Keep them close to the ground and close to your body," Lopez Matosov says.

2. Position Your Shins Parallel

You don't ​have​ to turn out your knees. Keeping tour shins parallel with each other puts less pressure on the core and back, she says.

3. Hold Your Legs in Tabletop

Instead of moving your legs with each rep, hold them stationary with your hips and knees at 90 degrees and your shins parallel with the floor. That way, you still recruit your lower abs, but you reduce the resistance on your core.

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