Lies, Damn Lies and Calorie Counters

Tuesday, June 13, 2006

Based on the volume of fan mail we get (and we read every letter that isn't ticking), many of you wonder about veracity of the calorie-counting functions on cardio exercise machines. Your suspicion is well-founded.

Treadmills, ellipticals, stationary cycles and similar units display two types of performance metrics, says Jim Zahniser, public relations manager of Precor, an equipment maker. The displays of heart rate, speed and distance are "straightforward and fairly accurate," Zahniser says. But the calorie counter is crafted to reflect the burn of an average exerciser, not you in particular, and thus it could be off by a bit, he says.

Caloric expenditure is mostly a function of distance covered and body weight, plus a variety of other factors, though there is some disagreement, as there often is in the exercise physiology field, about what those factors are (heart rate? sex? hair color?) and how much they matter. The machine can account for body weight and distance but not all other factors, so it uses averages.

For all their shortcomings, the machines' calculations are based on sound science, says Conrad Earnest, chief exercise physiologist at the Cooper Institute in Dallas.

"It is possible to calculate energy expenditure . . . with reasonable accuracy," he said, using just body weight and treadmill running distance. "It will never be 100 percent accurate. But the equations . . . have been validated."

Cardio machine maker Life Fitness does its own testing to set its equipment. "Subjects use the exercise equipment at various exertion levels, while their metabolic responses such as oxygen consumption and carbon dioxide output are recorded [and] converted to caloric output," explains Juliette Daly, Life Fitness staff biomechanics engineer. "We test a large subject pool at several exercise settings" to yield readouts more reflective of the general population.

Yet she too concedes that these more ambitious measures do not account for individual differences.

That doesn't make the readouts worthless. Say you hit the treadmill for 30 minutes today and, according to the machine, use 400 calories. You might really have burned 323 or 491. But if you work out on the same machine on Thursday, you can see whether you're meeting, beating or falling short of your prior performance.

Now, for the frequently asked question about calorie counts on elliptical machines, which are invariably higher than those for similarly long sessions on treadmills: Should you ellipticize to burn more calories?

Perhaps, particularly if the machine also has moving handles that engage the arms and shoulders, says William J. Kraemer, a kinesiology professor at the Human Performance Laboratory at the University of Connecticut in Storrs.

Caloric burn "depends on how much muscle mass is engaged," he says. "So if you are using your arms or a greater range of motion [per stride], you could burn more." Given similar duration and heart rates for the two workouts, however, the elliptical-vs.-treadmill difference is likely to be small.

Yes, ignoring calorie counts seems downright un-American and, sure, we often advise you to expend more calories than you consume if you want to lose weight. This, of course, requires some sort of estimate of calorie expenditure. So use the rough numbers on the machines. But remember, your body is an unerring tabulator of caloric balance. Feed it more calories than it burns, and it gets bigger. Use more than it takes in, it gets smaller. In the end, that's the calculation that matters.

No chat today; back next week.

-- John Briley


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