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Is Your Brand of Activity Tracker Really Accurate?

Tim Boyer's picture
Activity Trackers Compared

New research reveals just how accurate your brand of activity tracker really is under semi-controlled testing conditions.


Researchers from Iowa State University report that not all activity trackers or fitness bands are equally accurate when it comes to giving you feedback on just how active you are; and thereby, how many calories you are actually burning. Their findings were recently published in the journal Medicine & Science in Sports & Exercise.

The purpose of the study was to evaluate the relative validity advertised by the makers of some popular activity trackers that people wear to monitor their heart rate, time spent exercising and calories burned during exercise and while inactive. These fitness bands have become increasingly popular as a way to motivate dieters to exercise and help them calculate their calorie intake and expenditure for weight loss.

To determine just how well these activity trackers compare against one another, 52 study participants were each fitted with five different brands of wrist-worn fitness bands that included Fitbit Flex, Jawbone UP 24, Misfit Shine, Nike+Fuelband SE, and the Polar Loop, as well as two research activity-grade monitors--the Actigraph GT3X+ on the waist, and the BodyMedia Core on the arm.

The accuracy of the activity trackers was concurrently monitored with a portable metabolic system measuring device called the “Oxycon Mobile” that could track and calculate an energy expenditure benchmark during different activity sessions. The test sessions the participants performed in while wearing the activity monitors included 20-minutes of self-selected sedentary activities of choice such as reading, watching videos or working at a computer; 25-minutes of aerobic exercise; and 25-minutes of resistance exercise with 5-minutes rest between each activity.

What the researchers found was that the accuracy of the activity trackers overall varied between 15 and 30 percent in both over- and underestimating actual activity levels. Furthermore, the devices rated differently between each other depending on the activities compared.

“By looking at the most commonly performed activities in exercise and daily living settings, we can examine where the errors occur,” said Yang Bai, lead author and a graduate research assistant in kinesiology. “As expected, some monitors overestimate or underestimate all three activities, but some monitors overestimate one type and underestimate the other two categories, which can cancel out if we don't measure them separately.”

For an overall comparison, the BodyMedia Core came out on top with an error rate of 15.3%, followed by the Actigraph GT3X+ (16.7%), the Fitbit Flex (16.8%), the Nike+ Fuelband SE (17.1%), the Jawbone UP24 (18.2%), and the Misfit Shine (30.4%).

In addition, it was also determined that the activity trackers were least accurate when it came to measuring your activity level during activities like strength training. The researchers explain that this is not surprising as the tracking devices are designed to detect acceleration and body movement that is more aligned with walking and running as opposed to lifting weights.

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Although the accuracy of the activity trackers have some error to them, the researchers concluded that fitness bands like the Fitbit Flex, the Jawbone UP24 and the Nike+ Fuelband SE are accurate enough, and can still play an important role toward getting dieters to increase and maintain their exercise levels.

“I think the key to a consumer is not so much if the activity monitor is accurate in terms of calories, but whether it’s motivational for them and keeps them accountable for activity in a day,” said Greg Welk, professor of kinesiology.

For more about activity trackers, here are some related articles with more information about how you can benefit your weight loss efforts by wearing one:

Are Wearable Lifestyle Activity Monitors a Good Investment for Weight Loss?

Easy Belly Fat Weight Loss Tactic Works, Say Scientists

How Many Steps Should We Walk Each Day?


Comparison of Consumer and Research Monitors under Semistructured SettingsMedicine & Science in Sports & Exercise, Published ahead-of-print July 6, 2015; Bai, Yang, et al.

Iowa State News “Activity trackers not as accurate for some activities, ISU study finds



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