ACE-Sponsored Research: Are Activity Trackers Accurate?

Activity-Tracker_mainFor anyone who knows me, I rely on my fitness tracking device A LOT. So I know for me, this study was interesting to me.

Activity trackers are everywhere these days, but when it comes to tracking steps and calories, are they really accurate? A new ACE-sponsored research study examined five popular activity trackers to determine whether or not they are worth your time or your money.

It’s that time of year, when everyone recommits to a more healthy lifestyle. Increasingly, people are turning to activity trackers—electronic devices that track everything from caloric expenditure to quality of sleep—to help them stay on course and meet their health and fitness goals.

An estimated 19 million devices were in use in 2014, and that number is expected to grow exponentially over the next few years. In fact, a recent report by Juniper Research predicts that the use of activity trackers—also called fitness wearables—will triple by 2018.

While all this new technology is really cool and some of it is really fun to use, very little published research exists demonstrating the accuracy or validity of these devices. How closely do they predict caloric expenditure or track the number of steps taken? Given the increasing prevalence of these devices, the American Council on Exercise enlisted a team of researchers from the Clinical Exercise Physiology program at the University of Wisconsin—La Crosse to examine five popular activity trackers to determine whether or not they are worth your time or your money.


Five popular activity trackers were chosen: Nike+ Fuelband ($99-$149), Fitbit Ultra ($99), Jawbone UP ($99), BodyMedia FitCore ($99) and the Adidas MiCoach ($199).

The Results

When it comes to tracking steps, the activity trackers were pretty reliable. All five devices predicted within 10% accuracy the number of steps taken during treadmill walking and running as well as during elliptical exercise. During agility drills, however, there was a larger underestimation but this was likely due to the variety of more complex movements. Smaller or quicker steps taken may not always register on the activity trackers and also appeared to lead to less arm movement, which would then affect the accuracy of the activity trackers that were worn on the arm or wrist.

The devices were a little less accurate when estimating energy expenditure. This is a very complicated process. It also involved incorporating data measured by the device into a regression equation within the devices software.

The Bottom Line

When choosing a device, researchers advise consumers to think about the information they want to track. If looking at steps taken, the Jawbone UP appears to be the best activity device to choose. If an individual is more concerned about calories, there was a wide variety of results, depending on what type of activity was being performed.

“Most devices are pretty good for measuring steps taken during traditional activities,” says Porcari. “Once you start getting outside of that—like elliptical or sports-related movements—it becomes harder to detect actual steps taken.”

“These activity trackers work best for lower-intensity activities such as walking,” adds Stackpool, who thinks these devices are especially beneficial to new exercisers. “It gives them a way to assess where they are, set goals and see improvements.”

And what about caloric expenditure?

“Predicting calorie burn is a complicated thing,” explains Porcari. “People vary how they move their arms, for example. Some are more efficient and some are more variable. Most devices probably won’t get within 10 to 15 percent accuracy because there is simply too much biological variability.”

But that doesn’t mean there still isn’t a benefit to using an activity tracker, says Stackpool. “Activity trackers show people how active they are throughout the day. Being sedentary 90 percent of the time and performing 30 minutes of exercise does not necessarily make a person ‘active.’”

By wearing the devices all day, people can see whether or not they need to add more activity throughout the day. In fact, according to Porcari. Studies show that people are 30 to 40 percent more active when they use activity trackers.” So, perhaps the absolute accuracy of the device is less important than the fact that they do a good job of getting people up and moving.

And that, says Stackpool, is the take-home message for consumers: Do whatever it takes—whatever works for you—to be more active. If wearing an activity tracker helps you do that, your best bet is to choose a device based on comfort, ease of use and whatever additional features might appeal to you.

Visit for the full data set and more information.


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