AVENTURA, Fla. -

A South Florida doctor designed color-coded strips that determine whether someone is burning fat or muscle during a workout.

Emergency room Dr. Boaz Rosenblat came up with the idea after a game of tennis.

"I smelled my sweat and I said, 'Oh my goodness. It smells like someone poured vinegar on me. What's wrong with me?'" he said. "It turns out I was breaking down muscle."

Rosenblat, like many, was exercising on an empty stomach. The smell was a by-product of his body breaking down muscle since it had no sugar to burn.

The fuel strips serve as a sort of mood ring for athletes. It tells users whether they're burning fat or muscle, and whether they need to pick up the pace or slow down.

"This technology says hey, when you get to this color, you're in the danger zone, and you have one or two things you can do," he said. "You can either start fueling to give yourself sugar to burn off the fuel or you need to slow down that gas pedal and start pushing on that brake."

"Super cool. It's perfect," said Darrah Gilderman. "You want to know how much you're burning, how much fat and sugar you're burning during a workout."

"Everybody burns fat differently, everybody's genetics is different, everybody's however they work out is differently," added Havi Heber. "This customizes the workout, even within a class."

Rosenblat said he often sees patients who damage their kidneys by pushing themselves too hard and breaking down muscle.