The fat burning zone is presumably the activity level at which your body will start burning fat for energy. If weight loss is the goal of your training, discovering and maintaining exercise levels in that area will maximize fat burning. This area is different from body to body and should be calculated to make the most of the amount of fat you burn. There are experts who argue that adjusting your heart rate to your eating zone is the best way to lose fat. However, figuring out what your zone is can help when exercising, just to help you adjust your intensity based on your heart rate.
Steps

Step 1. Use the formula
To determine your fat burning zone, the first thing to do is estimate your maximum heart rate (MHR). To do this, subtract your age from 220 if you are a man; and from 226 if you are a woman. This is your maximum rate based on your average and gender. The fat burning zone is usually between 60 and 70% of your MHR. Therefore a 40-year-old man will have a maximum heart rate of 180, and his consumption zone should be between 108 and 126 bpm (beats per minute)

Step 2. Use a heart rate monitor
It is a chest strap that transmits information to a special watch. Using it you will get a better idea of where your consumption zone is. The heart rate monitor will take your heart rate as you exercise and use the real information to then calculate your zone

Step 3. Take a VO2 Max test
It is a test that measures the maximum volume of oxygen: it will accurately record your body's ability to carry oxygen during exercise. This test requires the participant to stand on a treadmill and breathe into a mask that measures oxygen and carbon dioxide levels as the heart rate increases. This information can be used to determine what bpm level your zone is at and how many calories you will consume in that zone
