The physiological theory behind Orangetheory Fitness is known as excess post-exercise oxygen consumption (EPOC). Participants are provided a heart-rate monitor, the new OTbeat Flex, OTbeat Pulse, or OTbeat Core chest strap, to monitor the five-zone interval training sessions called the Orange 60. During the course of a one-hour session, participants perform multiple intervals designed to produce at least 12 minutes of training at 84% or higher of their individual maximum heart rate, which translates to Zone 4/5. Participants use the entire body, stimulating metabolism and feeling increased energy after each interval. This program design produces EPOC, which is the workout “after-burn” effect: after the session, the body continues to need oxygen at a higher rate than before the exercise began - also known as oxygen debt. The body continues to use oxygen and burn more calories as if you were still working out, resulting in a 200-400 calorie increase to metabolism for 24-36 hours after the Orangetheory Fitness workout.