Fitness Trackers Up To 40% Inaccurate: Fitbit, Jawbone, Nike, Others Tested in New Study

A new study shows that popular wearable fitness trackers are often extremely inaccurate and vary among brands. Researcher's results showed all the trackers to be between 15 to 40 percent off in tracking user activity.

Fitness trackers are one of the most popular technology gadgets of the past year, with over 70 million sold in 2014 alone, and sales expected to rise in 2015. The trackers were among the most popular gifts this past holiday season as well, but a new research study shows that some of the trackers may not be doing their job.

Iowa State University did a study to determine exactly how accurate 7 popular fitness trackers were at correctly assessing the calories burned by those wearing them. A test group of over 50 healthy individuals between the ages of 18 and 65 wore all seven trackers simultaneously. Each participant engaged in three types of activity: sedentary for 20 minutes, aerobic for 25 minutes, and resistance for 25 minutes, with a 5 minute rest in between activities. The fitness trackers worn were Actigraph GT3X+, BodyMedia Core, Fitbit Flex, Polar Loop, Misfit Shine, Nike+Fuelband SE and the Jawbone UP.

The researchers were testing for accuracy in measuring calories burned by each participant, and used a breath monitoring system called Oxycon Mobile, which is proven to accurately determine calorie usage via oxygen measurement.

All of the fitness trackers were determined to be off in measuring calories burned by at least 15 percent, with the best performers, the BodyMedia Core and Fitbit Flex, just over 15 percent off. The Jawbone, Actigraph and Nike products weren't much further off, but the Misfit Shine was over 30 percent off and the Polar Loop was 40 percent inaccurate in its measurements.

This study echoed the results of an earlier study last year at Iowa State, which also found the Bodymedia Core and Fitbit Flex to be the most accurate. Gregory Welk, leader of that study, said buyers should be more educated as to the accuracy of the various trackers available. "People buy these activity monitors assuming they work, but some of them are not that accurate or have never been tested before," he said. "These companies just produce a nice-looking device with a fancy display and people buy it."