How to do the 12

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ST. PETERSBURG, Fla. — The 12-3-30 treadmill challenge has a lot of people checking the cardio box in the gym and sharing their workouts on social media.

Brady Malone, head coach at Orange Theory Fitness in downtown St. Petersburg walked us through the workout.

This viral trend is walking at 3 miles per hour, at a 12 percent incline, for 30 minutes," he explained.

The key is to avoid holding onto the treadmill and keep your arms pumping like you would outdoors.

"You burn more calories moving your arms. You’re also going to prevent injury. It's a little more functional. A joke I’ll make in class sometimes is, if you don't walk with a walker outside, try not to hold on here," Coach Brady said.

He also gave us some tips on form to get the most out of the viral cardio workout.

"Especially with this steep of an incline, you do want to lean forward a little bit so that your hips are staying underneath your feet, and you should feel it a little more in the back of your legs. Your glutes, your hamstrings, your calves are kind of pulling you up," he said.

If you try the challenge and find it to be too challenging, Brady said "take those same ratios and cut it in half, so if it's down one mile an hour, down maybe two or three percent incline – you’re doing something similar."

According to Coach Brady, you should aim to add cardio into your workouts two to three times a week, or about 60 minutes a week.

And while the challenge is a good way to get that cardio hour in, Brady said, "Just like anything, at some point, your intensity is going to have to change to continue to see results."