Planks are tough, but you probably wouldn’t call them nightmarish.

Until now.

This version of the exercise comes from Dean Somerset, C.S.C.S., an exercise physiologist in Edmonton, Alberta Canada. In just 10 seconds, your abs will feel as if they’re dancing with the devil.

Try it: Get into a plank position, your body in a straight line and your weight resting on your toes and forearms. Slightly push your forearms against the floor while pressing your shoulders and upper back away from your body.

Now tense all of your muscles, trying to make each one feel as if it’s hard as marble. Check off each body part in your mind, making sure you’re squeezing it. Go from your fingers all the way to your toes.

Here’s where the exercise goes from bad to tough as hell. Continue to keep your body tense as you inhale through your nose. Try to expand your lungs with air as if you were inflating balloons.

Then exhale. Pretend the air is toxic, and forcefully push out every last molecule of air from your lungs. That’s one “rep.” Keep tight and repeat for as many reps as you can. Stop the set when you lose that intense tension throughout your body—if you do this exercise correctly, you will probably only be able to do 5 reps before your entire core feels as if it’s on fire. And that’s if you’re really strong.

So why does just 10 seconds of this exercise feel harder than holding a regular old plank for minutes?

“It all comes down to the percentage of muscle you’re activating,” says Somerset. “Creating that high level of tension in the body activates all of your muscles to a greater degree.”

He says that difference between this plank and holding a “regular” plank for a minute or two is like the difference between doing one 500-pound deadlift and ten 50-pound deadlifts. “The more tension you can develop in a muscle, the greater the muscle and strength building opportunity you give it.”

Also, your abs drive respiration. “When you force all the air out with each breath, you have to activate your abs to an even greater degree than you would doing more shallow, less active breathing,” he explains.

In fact, five sets of five reps of this diabolical plank can improve your core strength, according to a study in The Journal of Strength and Conditioning Research. That’s what the scientists concluded when they found that guys who did a four-times-weekly abs workout that included this exercise significantly improved their core stiffness (a measure of strength) in just six weeks. And bolstering your core protects your spine and knees from injury and makes you a more explosive athlete, say the scientists.

Does this mean you should never return to your regular old planks, the ones you’d hold for as long as possible? “No,” says Somerset. “Those planks train strength-endurance rather than maximum strength. You need core strength endurance for situations when your core has to be engaged for longer than usual, like sitting upright, bending over while gardening, or playing sports.”

But start to hold those regular planks—and any other static abs exercise, like side planks, L-sits, or hollow body holds—for breaths instead of time. “That forces you to actually breathe through the exercise, activating your abs more, instead of putting you in a place where you’re just trying to survive for 10, 30, or 60 seconds,” says Somerset. “It’s an instant shift to quality over quantity.”

So test your core strength endurance by doing this same plank but with less total-body tension and more breaths. Keep your body about half as tight, and shoot for up to 30 breaths.