If you’ve been on a treadmill or elliptical you’ve probably seen those flashy heart rate training zone charts. These usually include fat burning and aerobic fitness zones. However, is there any research to support these heart rate training zones?
One study had 36 runners run on a treadmill at a progressively increasing intensity while being tested for heart rate, VO2max and fat oxidation. The researchers found that there were, in fact, heart rate training zones that optimized fat oxidation and aerobic fitness. Conveniently, those 2 zones also happened to overlap. The researchers found that aerobic fitness is maximized between 120.9 and 155.8 beats per minute, while fat burning is optimized between 105.4 and 136.3 beats per minute. The percent of max heart rate is between 67.6% and 87.1% for the aerobic zone and between 58.9% and 76.2% for the fat burning zone.
From a physiological standpoint, the body burns a high percentage of calories from fat when exercising at lower intensities. This happens because the body prefers to use carbohydrates as you increase intensity given they breakdown more efficiently. However, as you increase in speed you also increase the number of total calories burned. So, as you increase intensity the total number of calories burned per minute go up, but the percentage of calories from fat goes down. What ends up happening is total fat calories burned increase up to a point and then decline as exercise becomes increasingly intense. Here’s what the researchers found:
Aerobic fitness is optimized at a higher rate as you push your body further, but not at the very intense point where your anaerobic system kicks in.
It’s good news that you can both burn an optimal amount of fat and increase your aerobic fitness at the same time. This optimal heart rate zone appears to be between 120.9 and 136.3 beats per minute (between 67.6% and 76.2% of your max heart rate). So, put on a heart rate monitor and try training in this zone!
Carey, Daniel G. “Quantifying differences in the “fat burning” zone and the aerobic zone: implications for training.” The Journal of Strength & Conditioning Research 23.7 (2009): 2090-2095.