There's nothing like that sense of accomplishment when you look down after sweating it out on your cardio machine of choice - whether it's a treadmill, elliptical or bike - and seeing a big number in the calories burned column. But don't be fooled.

Also check out... Do You Need a Cardio Change? Fat-Burning Secrets for Cardio Workouts Shake Up Your Cardio Routine What Should Your Heart Rate Be?

When you put in all that personal info - weight, gender, age, etc. - at the beginning of your workout, the number it spits out at the end is simply an estimate that can err by dozens or even hundreds of calories! On average, most people burn about 100 calories per mile traveled on a cardio machine. If your machine estimates your burn way higher, then take note. And just because the program you choose is labeled "fat burning" doesn't mean that's what you're doing. A fat-burning workout means you might be burning fewer calories because it's designed to keep you a bit lower than your maximum heart rate.