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. Painting over graffiti: 342. Digging worms: 272. Cleaning out an illegal dump site: 450 calories.

"People have measured just about everything," says John Porcari, an exercise researcher at the University of Wisconsin-La Crosse.

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).

There are other methods for extracting this data. One is to collect exhaled air in special bags and then measure the volume and gaseous constituents of the collected air. Another is to place a person in a room, have the person perform an activity, then measure the exhalations afterward.

But Dr. James Levine, an endocrinologist and professor of medicine at the Mayo Clinic in Rochester, Minn., gets the prize for the most creative and exhaustive study of calories spent on daily activities. He outfitted 20 volunteers in special underwear with sensors similar to those used to monitor jet fighter motion.

By tracking small motions, while controlling diet to the last scrap of food, he's tracked calories expended in motions most of us don't think about — such as tapping fingers, pacing and fidgeting. Last year, he reported in the journal Science that the extra energy burned by people who tended to fidget was on average about 350 calories a day.

By now, most of our standard daily activities have been thoroughly researched — including kissing, fertilizing the lawn and washing the dog. But investigators are still cataloging more exotic pursuits.

Researchers are quick to point out that the values they arrive at — though reasonably consistent — are by no means absolute, because of myriad individual differences in how an activity may be performed.

For example, two people playing tennis might burn calories very differently. One might play with great intensity, while another might play the game walking.

The point to keep in mind about such calorie estimates is that although the figures aren't precisely accurate, they're useful for comparing activities, says Dr. Robert Rizza, an endocrinologist and professor of medicine at the Mayo Clinic.

"I'm looking at something on my wall," Rizza says. "It says jogging 6 miles an hour at 150 pounds is 11.6 calories a minute, and mowing grass is 4.1 calories per minute. When I'm jogging, am I really expending 11.6 calories? I don't know that for sure, but I certainly know I'm burning more calories jogging than mowing the lawn."

Ironically, the steady infiltration of time- and labor-saving devices into homes and the workplace over the past century — designed to make our lives easier — has made our lives a little too easy, doctors say. Cars have replaced walking, manual tasks have been replaced by computers and television has tethered us to the couch. What we've gained in convenience we've lost in physical activity.

Huge demographic shifts also have contributed to a decline in daily activity. A century ago, says Levine of the Mayo Clinic, most of the U.S. population lived in rural areas, many of them farmers. Today, according to 2000 census figures, about 80 percent of the population is squeezed into urban areas. The result, he says, is a sedentary society.

Levine has fashioned a solution, at least for him. He has turned his computer station into a treadmill, and walks while he works. "A very powerful way of burning calories is to get yourself on two legs, standing," he says. "As soon as you walk at 1 mile an hour — I call that shopping speed in Los Angeles — you double your metabolic rate." Levine says he's burning 100 calories an hour simply working at his computer or talking on the phone.

Those who don't want to go that far can try another strategy: reintroducing small amounts of exercise into one's everyday routine.

"Go back to some of the old ways of doing things," says Dr. Harvey Simon, associate professor at Harvard Medical School and author of "The No Sweat Exercise Plan."

"Treat exercise as an opportunity instead of a punishment. Use a hand mower, instead of a gas mower. Wash the car yourself. Do housework yourself instead of hiring someone to do it.

"It's the little things that count."