Accuracy of Fitbit Devices: Systematic Review and Narrative Syntheses of Quantitative Data

Abstract

BackgroundAlthough designed as a consumer product to help motivate individuals to be physically active, Fitbit activity trackers are becoming increasingly popular as measurement tools in physical activity and health promotion research and are also commonly used to inform health care decisions.ObjectiveThe objective of this review was to systematically evaluate and report measurement accuracy for Fitbit activity trackers in controlled and free-living settings.MethodsWe conducted electronic searches using PubMed, EMBASE, CINAHL, and SPORTDiscus databases with a supplementary Google Scholar search. We considered original research published in English comparing Fitbit versus a reference- or research-standard criterion in healthy adults and those living with any health condition or disability. We assessed risk of bias using a modification of the Consensus-Based Standards for the Selection of Health Status Measurement Instruments. We explored measurement accuracy for steps, energy expenditure, sleep, time in activity, and distance using group percentage differences as the common rubric for error comparisons. We conducted descriptive analyses for frequency of accuracy comparisons within a ±3% error in controlled and ±10% error in free-living settings and assessed for potential bias of over- or underestimation. We secondarily explored how variations in body placement, ambulation speed, or type of activity influenced accuracy.ResultsWe included 67 studies. 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. Findings also suggested a greater tendency to provide accurate measures for steps 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. 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. However, further accuracy studies are warranted. Our point estimations for mean or median percentage error gave equal weighting to all accuracy comparisons, possibly misrepresenting the true point estimate for measurement bias for some of the testing conditions we examined.ConclusionsOther 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.

Comparison of Physical Activity Measures Derived From the Fitbit Flex and the ActiGraph GT3X+ in an Employee Population With Chronic Knee Symptoms

“…In their review, Evenson et al (11) did not focus primarily on the amount of time spent in PA-intensity categories. In their review, Feehan et al (12) focused on the accuracy of measures derived from Fitbit devices and noted that there was a tendency for the Fitbit to overestimate MVPA in free-living settings compared with an ActiGraph accelerometer, similar to our study. In their review, Feehan et al (12) focused on the accuracy of measures derived from Fitbit devices and noted that there was a tendency for the Fitbit to overestimate MVPA in free-living settings compared with an ActiGraph accelerometer, similar to our study.…”

Postoperative complications and mobilisation following major abdominal surgery with vs. without fitness tracker-based feedback (EXPELLIARMUS): study protocol for a student-led multicentre randomised controlled trial (CHIR-Net SIGMA study group)

“…FTs are becoming increasingly popular as measurement tools in clinical research [23]. Potential advantages of using FTs in postoperative surgical patients are (1) real-time continuous feedback; (2) objective, validated outcome measurement of physical activity including step counts rather than subjective, error-prone assessment by patients themselves or hospital staff; (3) reduction of staff time and manpower to enforce mobilisation targets, thereby (4) increasing the cost-effectiveness of mobilisation interventions, which has been identified as a main barrier to its implementation [62].…”

“…First, the accuracy of commercially available devices in the clinical setting is low (see e.g. [23,66,67]) owing to specificities of the postoperative period like shuffling gait. Second, concerns about data protection are inadequately addressed by commercial FTs.…”

“…Although designed as a consumer product to help motivate individuals to be physically active, wearable fitness trackers (FTs) are becoming increasingly popular as measurement tools in clinical research [23]. Importantly, FTs can be used to objectively measure outcomes like steps or distance covered and can thus be used as a feedback tool to meet prespecified mobilisation targets through feedback via the FT display.…”

Continuous Digital Assessment for Weight Loss Surgery Patients

“…Only participants with connected Fitbit device data (n = 675) were used in the analysis. Fitbit devices have been found to be valid and reliable for capturing step, heart rate, and sleep data [11][12][13][14]. We restricted the analysis to the time period encompassing 12 weeks (84 days) before to 12 weeks after the participants' reported procedure dates (n = 520).…”