Fitbit Charge HR Wireless Heart Rate Monitor: Validation Study Conducted Under Free-Living Conditions
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Abstract
BACKGROUND: Many modern smart watches and activity trackers feature an optical sensor that estimates the wearer's heart rate. Recent studies have evaluated the performance of these consumer devices in the laboratory. OBJECTIVE: The objective of our study was to examine the accuracy and sensitivity of a common wrist-worn tracker device in measuring heart rates and detecting 1-min bouts of moderate to vigorous physical activity (MVPA) under free-living conditions. METHODS: Ten healthy volunteers were recruited from a large university in Singapore to participate in a limited field test, followed by a month of continuous data collection. During the field test, each participant would wear one Fitbit Charge HR activity tracker and one Polar H6 heart rate monitor. Fitbit measures were accessed at 1-min intervals, while Polar readings were available for 10-s intervals. We derived intraclass correlation coefficients (ICCs) for individual participants comparing heart rate estimates. We applied Centers for Disease Control and Prevention heart rate zone cut-offs to ascertain the sensitivity and specificity of Fitbit in identifying 1-min epochs falling into MVPA heart rate zone. RESULTS: We collected paired heart rate data for 2509 1-min epochs in 10 individuals under free-living conditions of 3 to 6 hours. The overall ICC comparing 1-min Fitbit measures with average 10-s Polar H6 measures for the same epoch was .83 (95% CI .63-.91). On average, the Fitbit tracker underestimated heart rate measures by -5.96 bpm (standard error, SE=0.18). At the low intensity heart rate zone, the underestimate was smaller at -4.22 bpm (SE=0.15). This underestimate grew to -16.2 bpm (SE=0.74) in the MVPA heart rate zone. Fitbit devices detected 52.9% (192/363) of MVPA heart rate zone epochs correctly. Positive and negative predictive values were 86.1% (192/223) and 92.52% (2115/2286), respectively. During subsequent 1 month of continuous data collection (270 person-days), only 3.9% of 1-min epochs could be categorized as MVPA according to heart rate zones. This measure was affected by decreasing wear time and adherence over the period of follow-up. CONCLUSIONS: Under free-living conditions, Fitbit trackers are affected by significant systematic errors. Improvements in tracker accuracy and sensitivity when measuring MVPA are required before they can be considered for use in the context of exercise prescription to promote better health.
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Three studies (five comparisons) examined wearable device heart rate compared with a Polar brand chest strap in free-living settings.
“Three studies (five comparisons) examined wearable device heart rate compared with the reference standard criterion measure of a Polar brand chest strap in free-living settings [75,77,78].”
From Reliability and Validity of Commercially Available Wearable Devices for Measuring Steps, Energy Expenditure, and Heart Rate: Systematic Review (2020) · cites this paper as [78]
Our approximation of wear time was based on available per-minute HR values, which may be an imperfect proxy because wearable device data are affected by motion artifacts.
“First, our approximation of wear time was based on available per-minute HR values, which have been used in previous studies22; however, wearable device data are affected by motion artifacts.64,65 Thus, our measure of wear time may be an imperfect proxy.”
From Association of Demographic and Socioeconomic Indicators With the Use of Wearable Devices Among Children (2023) · cites this paper as [22]
Previous studies have used heart rate as a proxy for wear time, such that time intervals with no acquired heart rate data were regarded as nonwear periods.
“Previous studies have used HR as a proxy for wear time22 such that time intervals with no acquired HR data were regarded as nonwear periods.44”
From Association of Demographic and Socioeconomic Indicators With the Use of Wearable Devices Among Children (2023) · cites this paper as [22]
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- Authors
- Gorny, A. W., Liew, S. J., Tan, C. S., & Müller-Riemenschneider, F.
- Affiliations
- National University of Singapore (SG)
- Corresponding author
- Gorny, Alexander Wilhelm
- Venue
- JMIR mHealth and uHealth
- Publisher
- JMIR Publications Inc.
- Published
- 2017-10-20
- Volume
- 5
- Issue
- 10
- Pages
- e157
- ISSN
- 2291-5222 (ISSN-L)
- PMC
- PMC5670315
- OpenAlex
- W2765080021
- Cited by
- 94
- References
- 29
- Citations by year
- 2026: 5 · 2025: 8 · 2024: 5 · 2023: 9 · 2022: 12 · 2021: 10 · 2020: 21 · 2019: 13 · 2018: 11
- FWCI
- 5.54
- Type
- journal article
- Language
- en
- Open access
- gold
- doi.org
- Licence
- cc-by
- Locations
- JMIR mhealth and uhealth (publishedVersion, cc-by)
- Europe PMC (PubMed Central) (publishedVersion, cc-by)
- PubMed Central (publishedVersion, cc-by)
- PubMed (publishedVersion)
- DOAJ (DOAJ: Directory of Open Access Journals) (submittedVersion, cc-by-sa)
- Refubium (Universitätsbibliothek der Freien Universität Berlin) (submittedVersion, cc-by)
- Universitätsbibliothek der FU Berlin Hochschulschriftenstelle u. Dokumentenserver (cc-by)
- Funders
- National University of Singapore
- Topics
- Physical Sciences › Engineering › Biomedical Engineering › Non-Invasive Vital Sign Monitoring
- Health Sciences › Medicine › Physiology › Physical Activity and Health
- Health Sciences › Health Professions › General Health Professions › Mobile Health and mHealth Applications
- Keywords
- wearable heart rate monitor, wearable activity trackers, moderate-to-vigorous physical activity, free-living conditions, device validation, measurement accuracy, smartwatches, physical activity monitoring, intraclass correlation coefficient, predictive value
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