02/26/2015 10:40 am ET Updated Feb 26, 2015

One Big Thing Fitness Trackers Haven't Mastered

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The American Council on Exercise (ACE) estimated that 19 million fitness trackers were in use last year. But, that doesn't mean they're all they're cracked up to be. According to a small, new study from ACE, these trackers may not be accurate at estimating calories burned.

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