Activity trackers may underestimate steps when walking is impaired

(Reuters Health) – Some wearable activity trackers can keep a fairly accurate count of steps for older people with ambulatory issues who use canes or walkers, but a few underestimate steps by a large margin, a recent study suggests.

“We were particularly surprised to see that even some of the wrist-worn devices were accurate among those with no walking impairments or those with mild walking impairments,” said senior author Matthew P. Buman of the College of Health Solutions at Arizona State University in Phoenix.

“Our results also demonstrated that both hip and wrist-worn devices were not accurate among those that used walkers or canes,” since walker and cane users have much different walking patterns and activity monitor sensors have not been designed to work in these populations, Buman told Reuters Health by email.

“According to the Centers for Disease Control and Prevention, more than a quarter of adults 65-74 years of age have difficulty with physical functioning activities,” he said. “This number increases to almost 50 percent by the age of 75.”

The researchers tested four widely available consumer wearable monitors, the Fitbit One and Omron HJ-112 mounted on the participants’ non-dominant hip and the Fitbit Flex and Jawbone UP mounted on the non-dominant wrist. A fifth device, the StepWatch monitor that is available to researchers, was mounted on the non-dominant ankle for comparison.

All but the Omron HJ-112 rely on accelerometers, which measure force and acceleration through so-called microelectromechanics. The Omron device is a pedometer, which relies on a mechanical pendulum that swings as a person walks to count each step. These devices cost between $30 and $100.

For the study, 99 people aged 62 years and older wore all of the monitors simultaneously and walked a predetermined 100-meter route at a local community center. The volunteers fell into four categories of mobility: About one quarter of participants could walk unimpaired, one quarter had some difficulty, one quarter used a cane and one quarter used a walker.

Researchers directly observed and counted each person’s steps to gauge the accuracy of the devices.

The FitBit One, Omron and Jawbone UP all underestimated actual steps by less than 10 percent for people walking without assistive devices, but had much larger margins of error for those using canes or walkers. The FitBit Flex underestimated steps significantly for all groups, according to the results in the Journals of Gerontology Series A: Biological Sciences and Medical Sciences.

Even for non-impaired adults, the FitBit Flex underestimated steps by almost 27 percent.

“Maintaining physical activity is very important as individuals age and wearable devices can play an important role in encouraging individuals to track their physical activity over time,” Buman said.

“Activity monitors are increasingly being discussed as an additional physical assessment tool that could be used by patients to share information with their health care providers,” added lead author Theresa A. Floegel of Arizona State University and the University of North Carolina – Chapel Hill.

Regardless of exact accuracy, tracking steps can help older adults move more, and most of their activity already comes from walking, said Tara O’Brien, assistant professor at the University of Tennessee Health Science Center in Memphis, who was not part of the new study.

“What’s really coming out in literature is that even a slight increase in activity will decrease chronic disease effects,” O’Brien told Reuters Health by phone.

Activity monitors worn on the wrist tend not to be accurate for older people with mobility issues, said Jung-Min Lee of the University of Nebraska Omaha who was also not part of the new study.

Wearing a simple pedometer on the waist is a good way to track steps, and only costs about $40, Lee told Reuters Health.

SOURCE: Journals of Gerontology Series A: Biological Sciences and Medical Sciences, online June 2, 2016.