How accurate are the calorie counts for various activities measured by wearable devices such as the popular Fitbit? Recent research in the Journal of Physical Activity & Health reported that such gizmos can over- or underestimate the energy expenditure of specific tasks by hundreds of calories. The study compared the results from a classic Fitbit, which was worn on an elastic band around the waist, to the numbers from a standard laboratory calorie-expenditure system (Oxycon).
For a jogging test, the calories burned according to the Fitbit were 18 short of those counted by the Oxycon system. On a test of one hour of cycling, the Fitbit underestimated calorie expenditure by 177. Conversely, the Fitbit overestimated the calories used in carrying groceries. The algorithm used in calculating calorie usage could be responsible for the difference, scientists said, along with variations in the placement of the Fitbit, which nonetheless can be useful for counting steps.