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Researchers suggest Fitbit indicators should not be used for public health surveillance

The Fitbit indicators of physical activity, resting heart rate and BMI did not provide sufficient evidence to use as a public health surveillance tool, according to a research letter published in American Journal of Preventive Medicine.

“One common source of personally generated health data comes from activity trackers, self-worn devices that provide feedback and long-term tracking on physical activity-related metrics. Using company-provided online tools, users can cross-tabulate three Fitbit indicators (steps, active minutes, resting heart rate) with diabetes, obesity or cardiovascular disease,” Kelly R. Evenson, PhD, MS, from the department of epidemiology at the Gillings School of Global Public Health University of North Carolina- Chapel Hill, and colleagues wrote. “An expert panel recommended assessing the psychometric properties of instruments for surveillance, but the validity of these Fitbit indicators is unknown.”

Researchers assessed the validity of using Fitbit indicators of physical activity (steps and active minutes), resting heart rate and BMI as a public health surveillance tool in the United States. Using data published by Fitbit in 2017 from more than 10 million adult Fitbit users between June 2015 and June 2016, they compared average steps per day, active minutes per day, resting heart rate and BMI to state- or district-based data from the 2015 Behavioral Risk Factor Surveillance System. Participants reported information on their physical activity, summed up in minutes/week for both total and vigorous intensity, over the past month including the type, duration and frequency. Maximal oxygen uptake (VO₂) was measured.

Evenson and colleagues found that both Fitbit indicators of physical activity, steps and active minutes, showed a poor association with VO₂ and a fair association with vigorous activity. Resting heart rate showed a weak association with VO₂ and total physical activity, and a fair association with vigorous activity, while the BMI Fitbit indicator showed a fair link to BMI. Although these results show that the four Fitbit indicators were not strongly associated with state- or district-based indicators, the correlations with Fitbit steps, active minutes and resting heart rate with vigorous activity is promising.

“Technology companies continue extending available features of wearable devices, improving data processing algorithms and enhancing individualized feedback,” Evenson and colleagues wrote. “Although enthusiasm for the use of such data for public health surveillance and interventions increases, companies are encouraged to derive metrics that are valid, reliable and generalizable.”

Previous research on personal fitness trackers has produced mixed results, with some studies suggesting that some of these devices accurately measure heart rate, but not energy expenditure, while others do not measure heart rate data accurately. – by Savannah Demko

Disclosures: The researchers report no relevant financial disclosures.