The workout is called Orange Theory Fitness, and it targets different heart rate zones - each represented by a rainbow of colors.
Here's how it works:
Everyone straps on a heart rate monitor. As they exercise, their numbers are displayed on overhead screens. The colors change when they reach a certain zone. Most work is done in the moderate zone. The green zone is challenging, but doable.
Then they take it up a notch to push pace, where you move into the orange zone to spike the metabolism and start conditioning the heart.
The trainers say that if you reach the orange zone and stay there for a certain amount of time, the body will burn more calories even after the workout has ended. That theory is based on a science known as EPOC (Excess Post-exercise Oxygen Consumption), and that's really why we breathe faster after we've had a period of strenuous activity. For several hours after the workout, you continue to have a really high metabolism and that's what turns into losing weight.
And with the monitors, the trainers are able to make sure everyone's where they need to be.