Keeping track of calories burned

Scientists are assigning values to everyday activities, from reading to finger-tapping to digging for worms


In the 10 minutes it takes to read this article, you'll expend about 15 calories, assuming you are sitting upright and weigh 150 pounds. If you are reading this while lying down, you will burn even less. If you plan to spend the next hour leaning over a casino table, you will 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 for 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 hooked 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 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 bags and then measure the volume and gaseous constituents of the collected air. Another is to place a person in a room or chamber, 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 in the military 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.

More testing

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.

Porcari, for example, has measured the calories expended dragging a deer, which required the help of 16 hunters and procuring several road kills from Wisconsin's Department of Natural Resources. Porcari "standardized" the deer to 125 pounds each by cutting off a leg or two.

"Dragging a deer is a common activity in Wisconsin," he says.

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, and yet another might dawdle at the net. A player with an efficient stroke may burn fewer calories than one who flails around. A heavy person will burn more calories than a thin one performing the same activity.

That's why the most accurate estimates will never rely upon just one reading, says Porcari, who has established calorie values for snowshoeing, rock climbing, in-line skating, Pilates, yoga and kickboxing, among others. (For testing outdoor activities, he uses a $30,000 "portable metabolic analyzer" that's strapped to the subject's back.) Porcari typically tests 15 to 20 subjects performing the activity under a variety of conditions, then establishes an average.

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