Fitness trackers over-estimate the number of steps their users take, analysis of 67 research reports suggests
Fitbit and other fitness trackers are inaccurate, misleading users by over-estimating the number of steps taken, according to researchers at the University of British Columbia.
The research, published in the medical journal JIMR Health, found that the devices have a habit of registering steps while users are undertaking other daily tasks.
The researchers reached their conclusions from studying 67 studies examining the accuracy of the Fitbit fitness tracker, the market leader.
"Consistent evidence indicated that Fitbit devices were likely to meet acceptable accuracy for step count approximately half the time, with a tendency to underestimate steps in controlled testing and overestimate steps in free-living settings," the authors concluded.
There are seemingly a limited number of situations where the device is likely to provide accurate measurement
They continued: "Consistent evidence indicated that Fitbit devices were unlikely to provide accurate measures for energy expenditure in any testing condition.
"Evidence from a few studies also suggested that, compared with research-grade accelerometers, Fitbit devices may provide similar measures for time in bed and time sleeping, while likely markedly overestimating time spent in higher-intensity activities and underestimating distance during faster-paced ambulation."
The study concluded: "...there are seemingly a limited number of situations where the device is likely to provide accurate measurement."
However, research tends to indicate that the inaccuracies are common to all fitness trackers, not just Fitbit.
In January last year, Sandra O'Connell, Gearóid Ólaighin and Leo Quinlan at the University of Galway analysed five physical fitness monitors and found that all of them tended to over-estimate the number of steps taken to a greater or lesser extent.
In its experiment, "participants wore five activity monitors simultaneously for a variety of prescribed activities including deskwork, taking an elevator, taking a bus journey, automobile driving, washing and drying dishes; functional reaching task; indoor cycling; outdoor cycling; and indoor rowing".
It tested the ActivPAL micro, the NL-2000 pedometer, the Withings Smart Activity Monitor Tracker (the Pulse O2), Fitbit One and the Jawbone UP.
All activity monitors registered a significant number of false positive steps per minute during one or more of the activities, the study concluded.
The Withings device, it advised, registered the fewest false positives and performed best overall, but "all monitors tested recorded steps when no steps actually took place (false positives) to a greater or lesser extent depending on the activity being performed".
The growing body of research will confirm widespread suspicions that fitness trackers are often inaccurate.
Fitbit, for example, is facing a class-action lawsuit from users (in the US, where else?) claiming that the company has oversold the technology.
V3 has contacted Fitbit for comment and will update the story as soon as the company responds.