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A systematic review on the accuracy of Fitbit devices

Fitbit’s are wearable devices that individuals can use to track their daily physical activity and increase motivation to do physical activity. Fitbit devices offer real time data on various aspects of daily life including number of steps taken, energy expenditure, time spent asleep, and time spent in different levels of activity. Fitbit devices are becoming increasingly popular in the health-conscious consumer public; they are also being used more frequently in research as measurement tools and to inform healthcare decisions. But are they accurate?

A team of researchers at Arthritis Research Canada and the University of British Columbia, lead by Dr. Lynne Freehan, recently conducted a study to find out how accurate Fitbit devices are as measurement tools. Currently, several devices exist that have been identified as a “research standard” for activity tracking. In this review, researchers measured Fitbit’s accuracy by comparing the readings to that of the research-grade devices.

The team used a specific research method known as a systematic review. Based on the eligibility criteria they have set up, the team selected a number of pre-existing studies that used both Fitbits as well as research-grade devices. They then combined the data from all of the studies to determine the accuracy of Fitbit devices. They explored measurement accuracy within each outcome category – steps, energy expenditure, sleep, time in activity, and distance – and used group percentage difference to help compare measurement errors and account for the diversity in outcomes and methods of study. A systematic review like this one provides a more powerful, complete picture on the accuracy of Fitbit devices than a single study would.

The data from 67 studies were reviewed. Below are some of the findings from the systemic review:

  • Fitbit devices provided acceptable measures of accuracy of steps taken approximately half the time
  • Fitbit showed a tendency to underestimate steps in controlled studies and overestimate steps in free-living settings (i.e. specified step count instruction vs. unspecified step count instruction)
  • Fitbits were unlikely to provide accurate measures of energy expenditure
  • Fitbits overestimated time spent in high-intensity activities and underestimated distance during faster-paced walking
  • Fitbit devices were most likely to provide accurate measures of steps in adults with no mobility limitations and when worn in the following ways:
    • on the torso for normal or self-paced walking
    • around the wrist for jogging
    • around the ankle for slow walking

 The significance of these research findings

The researchers concluded that:

“Other than for measures of steps in adults with no limitations in mobility, discretion should be used when considering the use of Fitbit devices as an outcome measurement tool in research or to inform health care decisions, as there are seemingly a limited number of situations where the device is likely to provide accurate measurement”

In addition to significant research implications, these findings are also important for Fitbit users in the general public, particularly those with mobility limitations or health conditions and diseases such as arthritis. Based on these findings, Fitbit is likely to underestimate your number of steps if you are walking very slowly. Some individuals may be relying on their Fitbit data to track improvements in their daily physical activity to measure their health or well-being. Fitbit devices are meant to motivate individuals, but if only a portion of someone’s steps are being measured, it could be very discouraging to people who have difficulty walking. As recommended in the research paper, wearing the device around the ankle when walking slowly may improve accuracy.

Overall, Fitbit remains a popular device and motivates individuals hoping to increase their daily physical activity. With that being said, it is important for arthritis patients to consider the possible inaccuracies when reviewing their data on their own or when using their data to inform healthcare decisions with their rheumatologist or other healthcare professionals.