The "fat-burning zone" is one of the many misconceptions that seem to be passed from one exerciser to another. The explanation for the myth is a combination of misinterpreted biochemistry and exercise physiology, inadequate education of many workers in the fitness industry, and a magazine culture that often favors sensationalism over scientific fact.
Let's start with a brief explanation of where this belief comes from.
Our body uses a mix of fat and carbohydrate to fuel the energy needs of our cells. Researchers can quantify this mix with high accuracy in an exercise physiology laboratory using expired gas analysis. The percent contribution of fat and carbohydrate does indeed vary depending on the intensity of exercise.
For instance, when we transition from rest to exercise, there is an increase in energy expenditure (i.e., calories burned) to meet the increased needs of our muscles. When the exercise is of a low intensity, our bodies preferentially use fat as a fuel, similar to a resting state. Thus, low intensity exercise does predominantly rely on fat to fuel contracting muscles................
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