How accurate is your fitness tracker?

Counting steps and calories burned are all in a day’s work for many people who rely on fitness trackers to reach their exercise goals. However, new research suggests that these devices may not be as accurate as manufacturers suggest.

Personal fitness trackers have solidified a place in mainstream society, as one in 10 adults wear a device, according to the NPD Connected Intelligence Consumers and Wearables Report.

In order to gauge just how accurate these devices are, Ball State University’s Clinical Exercise Physiology program conducted a study of six brands – Fitbit Charge HR, Fitbit Zip, Jawbone UP3, Garmin Vivosmart HR, iFit Vue and Misfit Flash.

The team tested each device while walking, running and climbing stairs. They then compared the data to medical devices used in the lab.

While some name brands tracked low and others high, the average error rates for all six devices were:

• Steps during walking or running – 2 to 3 percent error
• Stairs – 8 percent error
• Distance – 14 percent error

The fitness trackers were even less accurate when it came to calories burned and heart rate. Most of the fitness trackers significantly over-reported the number of calories burned.

For example, one of the test participants burned 55.2 calories during walks, according to the lab’s medical monitoring devices. However, the fitness trackers all said the participant burned a lot more than that. For example, the Misfit Flash reported 98 calories, which is 77 percent over-estimation.

“In general, I think we need to be really careful of the calorie counts,” said Dr. Alex Montoye, director of the study, in a news release. “If someone’s off every day in how much they think they should be eating to lose weight or maintain weight, over a period of time that can translate into huge weight gain or weight loss.”

Only two of the six devices – Fitbit Charge HR and Garmin Vivosmart HR – track heart rate on demand. Researchers reported that in one case a test participant had a heart rate of 91 beats per minute; however, Fitbit Charge HR calculated it at 68 beats per minute. The Garmin fitness tracker over-counted heart rate, showing 96 beats per minute when it was actually 69 beats per minute. The average heart rate error for the Garmin was about 10 percent and 14 percent for Fitbit Charge HR.

Montoye says calculating a heart rate that’s off by 20 to 30 beats per minute can be dangerous, especially for those at high risk of heart disease.

Despite some shortcomings with the fitness trackers, they can be a good tool to motivate people, says Jenny Showalter, a fitness specialist at Advocate Good Samaritan Hospital’s Health and Wellness Center in Downers Grove, Ill.

“Finding motivation to exercise can come from many influences, whether it be from a personal trainer, a friend or a fitness tracker,” says Showalter. “If seeing the physical reminder of a watch or device helps someone move every day, then I believe it has benefits. Because some of these devices vary with accuracy, each person should keep in mind that how they are feeling while they are exercising is most important.”