Exercise is not a one-size-fits-all type of deal, according to a study released today in the British Journal of Sports Medicine. Different people have to work out at different intensities to burn the most fat, to reach what researchers call the "Fat Max."

For overweight 12-year-old boys studied by the researchers, moderate exercises can go a long way toward weight loss.

They figured this out by having 30 boys – 17 of them overweight, 13 of them skinny – do cycling exercises.

The results showed that the overweight boys reached their "Fat Max" at lower intensities than the healthier boys. Working out harder did not burn more fat for them.

Why does this happen? The researchers give a couple reasons:
1. If you are overweight, your muscles don't have as good a capacity to use fat as fuel.
2. Your weight affects the type of muscles you have. Leaner people have a higher proportion of type 1 muscle fibers that burn off more fat. Heavy people have more type 2 muscles that burn off more carbohydrates.

What's your Fat Max? Michael Stefano, author of The Firefighter's Workout Book, has worked out a formula.

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