You're burning calories right now

In the 10 minutes it takes to read this article, you'll expend about 15 calories, assuming you're sitting upright and weigh 150 pounds. If you're reading this while lying down, you'll burn even less. If you plan to spend the next hour leaning over a casino table, you'll burn 156 calories. Praying to hit the jackpot? Praying (while kneeling) is 68 calories.

Scientists have assigned a calorie value to a dizzying array of activities. Cleaning out an illegal dump site: 450 calories. Painting over graffiti: 342. Digging worms: 272.

"People have measured just about everything," says John Porcari, an exercise researcher at the University of Wisconsin at La Crosse. "They've compared regular vacuuming to self-propelled vacuuming. Hand-held snow blowers to automatic ones."

For more than a century, scientists studying calories and physical activity have approached the task in pretty much the same way -- slapping masks on subjects and analyzing their exhalations. But now scientists can do it more accurately. Some, in fact, are taking calorie-counting to a new level, outfitting subjects with high-tech underwear packed with delicate motion sensors that can track calories expended in activities as minute as twitching.

It may be tempting to dismiss the idea of assigning calorie values to everyday activities as a frivolous parlor game, but the research, these scientists say, is providing a trove of data on why some people stay lean while others slide into obesity, and documenting historic declines in daily activity that are slowly expanding the American waistline.

"You can go through a wide range of occupations and household chores," says William Haskell, a professor of medicine at Stanford University School of Medicine, "and see there have been small declines, day in and day out, at work and at home."

Typically, calorimetric measurement involves having a subject perform an activity while breathing into a mask or under a hood or canopy that's hooked up to an analyzer.

The analyzer, which looks like a small printer, measures the volume of air a person breathes during the activity, as well as the oxygen and carbon dioxide inhaled and exhaled.

Based on this information, scientists can calculate the amount of oxygen that was used during the activity, which then can be used to determine the number of calories burned. (Exactly 4.825 calories are burned for each liter of oxygen).