TIME Exercise/Fitness

Find Out How Accurate Your Trendy Fitness Monitor Is

Photo by Bob Elbert

Fitness trackers like Jawbone Up and Fitbit are growing in popularity, but scientists wonder how accurate they really are. Researchers from Iowa State University compared eight popular brands

Activity monitors used to be tools that only scientists used during research, but the fitness-tracking industry, which is projected by analysts to be a $19 billion business by 2018. But how accurate are they really?

In a new study from Iowa State University published in the journal Medicine & Science In Sports and Exercise, researchers assessed how well they actually work. To test the products, 30 men and 30 women wore eight popular monitors during a 69-minute workout that included exercises like Wii tennis, running, and playing basketball. They also wore a medical-grade metabolic analyzer for comparison. The researchers found that some devices were pretty accurate, with estimates within 10 to 15% of precise calorie burn.

Here’s their list, ranked from most to least accurate:

1. BodyMedia FIT performed best with a 9.3% error rating. The researchers say this device has a similar accuracy to devices used in research. That’s probably because 10 years prior to releasing a consumer product, BodyMedia was developing products specifically for the medical research industry.

2. Fitbit Zip had a 10.1% error rating

3. Fitbit One had a 10.4% error rating

4. Jawbone Up had 12.2% error rating

5. Actigraph had a 12.6% error rating

6. Directlife had a 12.8% error rating

7. Nike Fuel Band had a 13% error rating

8. Basis Band had a 23.5% error rating

You can read more about the researchers’ work, here.

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