Burn Notice: How Accurate Are Devices That Track Calories Use

“Activity monitors using accelerometers can aid in weight control by estimating the calories you expend during the day, according to companies that sell them. Scientists say that the gadgets can be good motivators, but that you shouldn't count on them for an accurate estimate of daily calorie burn. ‘You can get a pretty good group [average] measure, but on an individual basis you may be off by 20% to 30% or more,’ says Patty Freedson, chairman of the kinesiology department at the University of Massachusetts in Amherst. The rate of error is likely to be consistent for a given person, so the devices ‘will be accurate in showing improvement’ in physical activity levels, she adds. BodyMedia says unpublished data, some of which the company sponsored, show that 75% of armband users will have an error of 10% or less using the armband, and 95% will have an error of 20% or less. Even if these devices can't perfectly estimate calorie burn, they can be good motivators, scientists say.”

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