A popular myth is that there is a specific range of heart rates in which you must exercise to burn fat. Even many cardio machines display a “fat-burning zone” on their panels, encouraging people to exercise in a specific heart rate range. Have you ever wondered if you really have to exercise in a specific heart rate zone to lose fat? And what happens if you venture out of that zone? Jason R. Karp, PhD, a nationally recognized speaker, writer and exercise physiologist who coaches recreational runners to Olympic hopefuls through his company, RunCoachJason.