I often have new clients ask me what the correct heart rate training zone should be for fat loss. I have recently read message boards and forums with claims that to lose fat you should stay in the 120-135 bpm zone. The rational comes from the fact that under low level activity our physiology uses much higher percentages of fat as a fuel source. While maintaining this pace for 20-30 minutes will render benefits in weight loss and conditioning and is a good course for older participants or those with restrictions, the fact is the caloric expenditure is too small.
First off let me say, always have a check up with a physician before undertaking a vigorous exercise program. That being said, you are better served burning the maximum amount of calories you're capable of in the time allowed. A calorie burned is a calorie not on you. Moderate and especially high intensity exercise causes the majority of calories to come from carbohydrates in the form of glucose or glycogen found in your muscle, blood and liver. Glycogen with the usage of oxygen (hence aerobic exercise) converts easily to a usable form of energy to power you. The truth is your system will continue to burn some fat for fuel as well as glucose in an effort to spare carbohydrate for other body functions. The real benefit comes from the fact that all this expended sugar needs to be replaced meaning more of the carbohydrates you eat will go toward restoring depleted glycogen stores and less of it stored as fat.
