How Many Calories Are You Really Burning?

Get Fired Up

Going for a run will erase the jumbo sundae you ate.... It's that simple, right?

We wish! Truth is, it depends on how long and fast you ran and how ginormous that sundae was. Surprised? You're not the only one: Research shows that many women overestimate the number of calories they're blasting daily, sometimes by nearly 1,000! Use our guide to learn -- and boost -- your burn.

The payoff of knowing how your body uses calories as fuel is that it can help you blast fat and change your shape. The basics: What you don't use goes straight into reserves (located in Bun 1 and Bun 2, your belly, your hips, your thighs). For every 3,500 calories you torch above and beyond your usual weekly intake, you slim down by about one pound.

As you sit there reading, you're burning about one calorie per minute. That number increases each time you stand, walk, or run to grab the phone, because your body needs more energy to get the job done. Scientists measure exercise intensity in METs (metabolic equivalents): The harder you work, the higher your METs. "For weight-loss and health benefits, you should do activities of at least three METs an hour -- enough to burn about 200 calories an hour -- most days of the week," says Barbara Ainsworth, PhD, MPH, a professor at Arizona State University who helped develop the Compendium of Physical Activity, a comprehensive calorie-burn database. As a general rule, your MET intensity rises as you:

• Move your muscles. Your lean tissue is your engine; the more you use, the more fuel you burn.
• Pull your own weight. Stand-up activities like running burn more calories at a higher level than those in which your weight is supported, such as cycling. The trade-off: You can usually do the sit-down activity longer to make up the difference.
• Work harder. A choppy swimmer burns more calories than one with a silky stroke. Walking uphill uses more energy than strolling the flats. And going faster is a surefire way to turn up the torch.