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Fat-burning claim: Exercising at lower intensity levels and for a longer duration burns more fat than moderate- to high-intensity exercise. People who subscribe to this theory use some of the same facts above regarding the source of fuel for various levels of exercise intensity. Further adding "credibility" to these claims, many cardio machines have "fat burning" workouts or programs, which have you exercising at lower heart rates.
Fat-burning fact: While it is a fact that low-intensity activities use more fat as fuel, this theory doesn’t hold up unless you can devote several hours every day to exercise. It’s important not to confuse percentage of fat burned with total amount of fat burned. Let's look at three examples of fuel usage, at three different intensity levels, and see which actually burns the most fat:
Fat-burning claim: You’ve heard it a million times—muscle burns more calories than fat, even while you’re sitting still. So when it comes to losing weight, strength training is more important than cardio.
Fat-burning fact: Part of this is true. A pound of muscle, at rest, burns about three times as many calories as a pound of fat, which by nature is pretty much always “at rest.” But whether or not strength training should be the only (or main) focus of your fitness program depends on what the numbers really say.