Is Your Fitness Tracker Lying?

Sporting an activity tracker has become a rite of passage for many fitness lovers. Of course, if you’re going to pony up the cash for a piece of fancy, wearable tech, you want it to work.

Unfortunately, researchers from Iowa State University found that your favorite fitness trackers are not so spot-on in terms of measuring the calories you burn throughout the day. The study, published in Medicine & Science in Sport & Exercise, compared data from eight different trackers. Researchers had 30 men and 30 women wear all of the devices during a 69-minute "workout" that involved 13 different types of activities, including running, Wii tennis, and playing on the computer. As a means of comparison, participants also wore a portable metabolic analyzer that measured their actual energy expenditure based on oxygen intake.

How did the trackers stack up? Researchers determined that the bands were “reasonably accurate,” with most calorie-burn readings registering between 10 and 15% of lab-tested stats. But, what we find most interesting is that the three top performers — BodyMedia FIT (9.3% error rating), Fitbit Zip (10.1% error rating), and Fitbit One (10.4% error rating) — are all designed to be worn either around your arm or at your hip, not at your wrist.

The forerunners are also priced close to $100, compared with the least accurate option, Basis Band, which retails at $199. “The devices have sufficient validity to provide consumers with a reasonable estimate of their physical activity behavior," says study co-author Gregory Welk, PhD, professor of kinesiology at the university. "But, the monitors will only help a person be physically active if they use the feedback to modify their behavior on a regular basis."

It’s also important to note that not everyone who sports a fitness tracker is focused on calorie expenditure — most monitors also track step count and sleep quality, providing helpful insight into your overall health and general activity level. Additionally, the devices used in this research aren’t the very-latest, souped-up models newly available on the market. But: "We are actually conducting another study this summer to test the newer versions of most of the devices, including the Fitbit Flex," Dr. Welk tells us.

Still, all this research data that's tracking data about data-trackers isn't just a tongue-twister; it also seems like a big step closer to creating the perfect model.

Below, the full rankings of fitness monitors from the study:

BodyMedia FIT (9.3% error rating)

Fitbit Zip (10.1% error rating)

Fitbit One (10.4% error rating)

Jawbone UP (12.2% error rating)

Actigraph (12.6% error rating)

Directlife (12.8% error rating)

Nike FuelBand (13.0% error rating)

Basis Band (23.5% error rating)