The Orange Theory

UNDATED (NBC) — It's an exercise craze that's sweeping the country. It trains the body to use more oxygen and burn more calories. It's called the "orange theory."

As you enter the workout zone, the music turns up and an orange glow shines down. It's time for an Orange Theory workout. But it's really not a 'theory;' it's exercise based on science.

"The science says if we can get your heart rate to 84-percent of your target zone 12 to 20 minutes inside a 60-minute workout then you'll see an elevated metabolic rate burning 500 to 1,000 calories during the work out," Terry Blachek, Orange Theory Fitness owner, said.

The science is backed by technology. Everyone in the class wears heart-monitoring straps with snap-on pods that track each individual's workout.

"And it's all being picked up on the screen," Blachek said. "So if you look at the screen, you know that you're working out at the proper level."

So it doesn't matter if you're a beginner or a seasoned athlete, you only need to worry about your numbers and exercising at your own pace. And there's no time for workout doldrums. From treadmills to rowers and TRX suspension, trainers lead you through a full-body workout. Before you know it, it's over.

"I don't [look] at the clock, I'm just in and out," Adrienne Venable, exercise enthusiast, said. "It's great it's so addictive."

Venable says it fits her fast-paced lifestyle and has finally helped her break a stubborn weight plateau.

"It's like so frustrating," Venable said. "I eat right."

Sam Singleton is just excited to be back in the game. He hasn't worked out in 10 years because nothing seemed to work until now.

"In the first week, I've lost 12 pounds and about 2 inches on my waist," Singleton said. "I'm learning how to work out every part of your body."