Heart-rate based interval training in a fun and energizing group environment! Burn calories after you workout? That's the Orange effect! The physiological theory behind Orangetheory is known as excess post-exercise oxygen consumption (EPOC). During the course of a session, you will perform focused 10-30 minute intervals that use your entire body and stimulate your metabolism. After each exercise, you will feel increased energy. After the session, your body will continue to burn more calories as it tries to recover from the strong bursts of activity.