What Your Fitness Tracker Gets Right and Few Ways It'll Miss the Mark

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Happy young woman using activity tracker

Wearable fitness trackers — including Fitbit and Jawbone devices — are wildly popular ways to keep a tally of all the daily activities you do. They count steps and calories, measure heart rate and, in some cases, monitor things like how much and how well you sleep. But before you live and die by those numbers on your device, you might want to consider something: How accurate is all that information anyway?

According to a new study by researchers at Ball State University’s Human Performance Lab, the answer is they are both very accurate and wildly inaccurate — depending on what they’re measuring. When it comes to counting steps, these trackers do a great job, as long as those steps are taken while walking or running. “But they all tended to underestimate the amount of activity subjects got while doing household chores like sweeping, cleaning and doing laundry,” said Alex Montoye, a clinical exercise physiology professor at Ball State University.

The researchers watched subjects perform various activities and used a tally counter to record every single step observed. They also had subjects hooked up to a metabolic analyzer to measure the amount of oxygen used, which relates directly to how many calories are being burned. This data was compared to the steps and calories recorded by the trackers the subjects wore.

While the number of steps recorded during walking and running were nearly spot-on, the trackers overestimated the number of calories burned during those activities by anywhere from 15 to 40 percent. That’s enough to negate that cookie you thought you earned during your workout.

None of these flaws are reason enough to stop using a fitness tracker, especially because these tools are powerful motivators for many people and do a great job at keeping you accountable to your activity goals on a daily basis. “The takeaway is to be careful not to take the numbers too literally,” cautions Montoye. “The number on your wrist doesn’t matter as much as the fact that you’re being active every day.”

Sally Wadyka is a Boulder, Colorado-based journalist who writes about nutrition, health and wellness.