Systematic Review of Fitbit Charge 2 Validation Studies for Exercise Tracking

Abstract

ContextThere are research-grade devices that have been validated to measure either heart rate (HR) by electrocardiography with a Polar chest strap or step count with ActiGraph accelerometer. However, wearable activity trackers that measure HR and steps concurrently have been tested against research-grade accelerometers and HR monitors with conflicting results. This review examines validation studies of the Fitbit Charge 2 (FBC2) for accuracy in measuring HR and step count and evaluates the device’s reliability for use by researchers and clinicians.DesignThis registered review was conducted using the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines. The risk-of-bias visualization (robvis) tool was used to assess the strength of each considered article.Eligibility CriteriaEligible articles published between 2018 and 2019 were identified using PubMed, the Cumulative Index to Nursing and Allied Health Literature, Embase, Cochran, and World of Science databases and hand searches. All articles were HR and/or step count validation studies for the FBC2 in adult ambulatory populations.Study SelectionEight articles were examined in accordance with the eligibility criteria alignment and agreement among the authors and research librarian.Main Outcome MeasuresConcordance correlation coefficients (CCC) were used to measure agreement between the tracker and criterion devices. Mean absolute percent error (MAPE) was used to average the individual absolute percent errors.ResultsStudies that measured CCC found that agreement between the FBC2 and criterion devices ranged between 26% and 92% for HR monitoring, decreasing in accuracy as exercise intensity increased. Inversely, CCC increased from 38% to 99% for step count when exercise intensity increased. HR error between MAPE was 9.21% to 68% and showed more error as exercise intensity increased. Step measurement error MAPE was 12% for healthy persons aged 24–72 yr but was reported at 46% in an older population with heart failure.ConclusionsRelative agreement with criterion and low-to-moderate MAPE were consistent in most studies reviewed and support validation of the FBC2 to accurately measure HR at low or moderate exercise intensities. However, more investigation controlling testing and measurement congruency is needed to validate step capabilities. The literature supports the validity of the FBC2 to accurately monitor HR, but for step count, it is inconclusive, so the device may not be suitable for recommended use in all populations.

Non-equivalent, but still valid: Establishing the construct validity of a consumer fitness tracker in persons with multiple sclerosis

“…However, only limited evidence of validity is available for any Fitbit device in MS populations. Existing validation studies are primarily conducted in healthy adults, and three recent systematic reviews of such studies cautiously support the validity of Fitbit-derived PA metrics [18][19][20][21]. However, validation studies also suggest that these metrics' accuracies decrease at low activity intensities [20], at slow walking speeds [18,[22][23][24], and with the use of walking aids [25].…”

“…Existing validation studies are primarily conducted in healthy adults, and three recent systematic reviews of such studies cautiously support the validity of Fitbit-derived PA metrics [18][19][20][21]. However, validation studies also suggest that these metrics' accuracies decrease at low activity intensities [20], at slow walking speeds [18,[22][23][24], and with the use of walking aids [25]. Not only do PwMS walk slower healthy controls, they also exhibit different abnormal gait patterns [26,27] and frequently adopt walking aids as their MS progresses [28,29].…”

Validation of an open-source smartphone step counting algorithm in clinical and non-clinical settings

“…Second, the wearable validation was performed with the use of a proprietary activity tracker (Fitbit Charge 2). Although this device has demonstrated reliable step counts during naturalistic gait performed in laboratory conditions (50,51), its accuracy in free-living conditions is inconclusive, and it is presumably dependent on the characteristics of the studied population (20,52,53). Importantly, the selected activity tracker was placed on the wrist, a body location that can be activated by many repetitive movements (e.g., gesticulating) while the rest of the body is still, hence it is more likely to overestimate steps compared to locations closer to the body mass center.…”

Using wearable activity trackers for research in the global south: Lessons learned from adolescent psychotherapy research in Kenya

“…The Fitbit Charge has a proven track record in large-scale research, especially in measuring heart rate variability (Natarajan et al, 2020), and its accuracy has been demonstrated in various studies (Evenson et al, 2015; Wahl et al, 2017; Germini et al, 2022; Irwin and Gary, 2022). Although the data quality from Fitbits is higher, we found it difficult to extract the data from the devices, specifically, the heart rate variability.…”