Study: Some activity trackers may not be as accurate as advertised

Several popular wearable activity trackers are good for counting steps, but inaccurately  estimate the number of calories expended, Alex Montoye, a clinical exercise physiology professor in Ball State University’s Human Performance Laboratory.


In a new report, Montoye’s research team examined the accuracy of the Fitbit’s One, Zip and Flex and Jawbone UP24 for estimating energy expenditure (commonly described as calories) and steps for specific activities and activity categories. Thirty participants tested the devices during sedentary acts (lying on a bed for 10 minutes),  household activities (sweeping, laundry and cleaning) and various exercises (walking, jogging, cycling).


“Our study found that the activity trackers we tested were simply not as accurate as many people believe,” Montoye said. “These devices overestimate the calories expended by 16 to 40 percent. These items provide accurate measures of steps for structured activity, similar to much less expensive pedometers.


“I think that activity trackers are very valuable, especially if they motivate people to be more active,” he said. “ However, I would not live or die by the step or calorie estimates but, rather, use them as a general idea of activity levels.  The websites and user manuals of many companies' devices even caution against over-valuing the accuracy of the data.”


The study found:

·      Activity trackers tested work well for counting steps taken while walking or running but do not correctly count steps during sedentary activities.

·      Step estimates were not accurate for household or chore-type activities.

·      For individuals who spend a lot of time sedentary or walking, the monitors work reasonably well for counting steps.  

·      For those who spent a large portion of the day doing household or other non-ambulatory, non-sedentary activities, the step estimates will likely be poorer.  

·      All monitors severely underestimated calories expended and steps during cycling.


Montoye also said while new monitors are being introduced regularly, little research has evaluated the ability of such devices to accurately measure heart rate or sleep duration and/or quality.  


“Just because the monitor may give fancy graphs of heart rate changes or depth of sleep, that does not mean the devices are accurate in their measurements. “


Contact Information

Montoye may be reached at 765-285-1811 or



Marc Ransford

Senior media strategist

Ball State University

Muncie, Ind. 47306


Twitter: @marcbsu