New Study Says Activity Trackers Can’t Accurately Calculate Your Calorie Burn

Research says you probably shouldn't trust your fitness tracker for stats about how many calories you're burning

From daily step totals to nightly sleep patterns, fitness fanatics have come to trust their activity trackers to tell them almost everything about their health and wellness.

However, according to a new study from the American Council on Exercise (ACE) which examined the accuracy of five popular activity trackers, you probably shouldn’t trust your wearable device to provide accurate stats about how many calories you’re burning.

According to the study results, when reporting energy expenditure (or calories burned) the trackers were off by anywhere from 13 to 60 percent. Some devices over-calculated and some under-calculated.

“Predicting caloric expenditure is a relatively complicated process,” ACE Chief Science Officer Cedric X. Bryant, Ph.D. said in a news release. “There are certain assumptions that are made when developing the algorithms that translate movement activity detected by the devices into calories burned. Even devices with the best prediction equations will have some margin of error due to natural biological variability.”

To determine the accuracy of some of the most popular fitness trackers on the market, researchers at the University of Wisconsin, LaCrosse worked with 10 healthy men and 10 healthy women ages 18 to 44. The study was divided into two parts: one to measure calorie burn and the other to measure steps taken, and it included the Nike+ Fuelband, Fitbit Ultra, Jawbone UP, BodyMedia FitCore, and the Adidas MiCoach.

The participants wore the trackers while walking and running on a level treadmill, while on an elliptical, and also while performing “sports-related” exercises and drills.

“To assess accuracy, all activity trackers evaluated in the study were compared to portable metabolic analyzers worn by all participants and the NL-2000i pedometer, which has been shown to be accurate in previous research studies,” ACE noted in the news release.

The results revealed that most of the devices were able to effectively measure the amount of steps that participants took while walking, running, and on the elliptical within 10 percent accuracy. However, they were found to have miscalculated steps when performing complicated movements like weight-lifting or cross training.

The study found that the most accurate step-counts were recorded with the Jawbone Up.

Even though the study found that these wearable devices can’t provide 100 percent accurate feedback, the study’s authors and ACE still feel that they can be worthwhile tools.

“Although the devices evaluated in the study aren’t ideal for measuring the number of calories burned, they can provide consumers with a reasonable estimate of how much physical activity they are incorporating into their daily routines,” Bryant said. “Having access to that information can be a valuable motivational and informational tool for people beginning a fitness journey, as well as those trying to increase their level of daily physical activity.”

He continued, “It is important for consumers to understand that while activity trackers may not precisely estimate caloric expenditure, they seem to accurately measure step counts during certain activities and can be used to effectively quantify and track changes in an individual’s physical-activity habits.”