If you're depending on your smartwatch to tell you the truth about how many calories you burned during a workout — well, don't.
Fitness trackers are great cheerleaders, delivering tiny doses of motivation with every celebratory chime, buzz and on-screen animation that marks a completed activity goal. But they are less reliable when it comes to measuring total energy expenditure during exercise.
In an independent evaluation, FIU researchers tested four of the most popular fitness watches against gold-standard clinical lab equipment and found they consistently overstated how many calories people burned. And the error wasn't the same for everyone, according to results published in PLOS One.
The higher a person's body fat, the greater the error tended to be — meaning people most likely to track calories for weight management may be getting some of the least accurate numbers.
"You can't treat the calories burned number it gives you as an accurate number, because it's not," said Jason Kostrna, the study's lead author and FIU associate professor of kinesiology and exercise science in the College of Arts, Sciences & Education. "You could be off hundreds of calories each week and easily end up in a calorie surplus when you think you're in a calorie deficit."
