Do you exercise in the "fat burning zone" -- that mysterious place determined by obscure heart rate formulas that tell you exactly where you should be exercising in order to burn the most fat? Perhaps you've noticed such a program on your treadmill or heard your aerobics teacher talking about it.

The fat burning zone is like an urban legend that just won't die. In other words, it's a lie -- or at best, it's misleading.

"Fat burning" is a vernacular expression, shorthand for what exercise professionals refer to as "the beta oxidation of fatty acids." Although "fat burning" sounds like cellulite melting in a furnace of exercise induced body heat, what actually happens is a little different.

At any given moment in time, you are burning (or, technically, oxidizing) fuel (food), that is to say, breaking it down for energy. The food you eat gets taken apart by the body, broken down into its smallest components (fatty acids, amino acids and glucose), which provide energy for the body to do anything and everything that it needs to do. That means providing energy to grow nails and hair, to breathe, to make enzymes, to digest food, to exercise, think, sit at the computer, garden, run for the bus and even sleep. The particular mix of fuel that it uses depends on a number of things.

The greatest proportion of your fuel comes from fat when your body is at rest. But the total number of calories burned is tiny. In other words, you're burning a high percentage of a very small number (about one calorie a minute in the average person).