Understanding your heart rate is important in order to measure the intensity of your exercise. As you can imagine, your heart rate will be lower when you're at rest (resting heart rate) and higher when you're exercising. Your fat-burning heart rate zone is when your body reaches a certain rate which allows your body to tap into fat stores instead of using basic carbohydrates for energy. Calculating Your Heart Rate for Fat Burning In order to calculate your heart rate for fat