In August 2018 researchers from Canada published the results of their review of the scientific literature to assess the accuracy of Fitbit devices. A total of 67 studies were included in the review. Results showed that Fitbit devices were accurate for step counting for only about half the time, with a tendency to underestimate steps in controlled testing and overestimate steps in free-living settings. Accurate step measurements were seen during normal or self-paced walking with torso placement, during jogging with wrist placement, and during slow or very slow walking with ankle placement in adults with no mobility limitations. However, there was consistent evidence that Fitbit devices were unlikely to provide accurate measurements for energy expenditure in any testing condition. In addition, similar measurements were seen for time in bed and for time sleeping, while there was an overestimation of time spent in higher-intensity activities and an underestimation of distance during faster-paced walking.
Feehan LM et al. Accuracy of Fitbit Devices: Systematic Review and Narrative Syntheses of Quantitative Data. JMIR Mhealth Uhealth. 2018 Aug 9;6(8) [Epub ahead of print]