Validity and Reliability of Fitbit Flex for Step Count, Moderate to Vigorous Physical Activity and Activity Energy Expenditure
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OBJECTIVES: To examine the validity and reliability of the Fitbit Flex against direct observation for measuring steps in the laboratory and against the Actigraph for step counts in free-living conditions and for moderate-to-vigorous physical activity (MVPA) and activity energy expenditure (AEE) overall. METHODS: Twenty-five adults (12 females, 13 males) wore a Fitbit Flex and an Actigraph GT3X+ during a laboratory based protocol (including walking, incline walking, running and stepping) and free-living conditions during a single day period to examine measurement of steps, AEE and MVPA. Twenty-four of the participants attended a second session using the same protocol. RESULTS: Intraclass correlations (ICC) for test-retest reliability of the Fitbit Flex were strong for walking (ICC = 0.57), moderate for stair stepping (ICC = 0.34), and weak for incline walking (ICC = 0.22) and jogging (ICC = 0.26). The Fitbit significantly undercounted walking steps in the laboratory (absolute proportional difference: 21.2%, 95%CI 13.0-29.4%), but it was more accurate, despite slightly over counting, for both jogging (6.4%, 95%CI 3.7-9.0%) and stair stepping (15.5%, 95%CI 10.1-20.9%). The Fitbit had higher coefficients of variation (Cv) for step counts compared to direct observation and the Actigraph. In free-living conditions, the average MVPA minutes were lower in the Fitbit (35.4 minutes) compared to the Actigraph (54.6 minutes), but AEE was greater from the Fitbit (808.1 calories) versus the Actigraph (538.9 calories). The coefficients of variation were similar for AEE for the Actigraph (Cv = 36.0) and Fitbit (Cv = 35.0), but lower in the Actigraph (Cv = 25.5) for MVPA against the Fitbit (Cv = 32.7). CONCLUSION: The Fitbit Flex has moderate validity for measuring physical activity relative to direct observation and the Actigraph. Test-rest reliability of the Fitbit was dependant on activity type and had greater variation between sessions compared to the Actigraph. Physical activity surveillance studies using the Fitbit Flex should consider the potential effect of measurement reactivity and undercounting of steps.
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Nine studies (22 comparisons) examined energy expenditure in free-living settings compared with doubly labeled water and accelerometry.
“Nine studies (22 comparisons) examined energy expenditure in free-living settings compared with the criterion measures of doubly labeled water [104] and accelerometry [29,49,79,101,131,172,174,175].”
From Reliability and Validity of Commercially Available Wearable Devices for Measuring Steps, Energy Expenditure, and Heart Rate: Systematic Review (2020) · cites this paper as [101]
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References 29 · Cited by 152
Research works printed but not linked: 3
- [1]Bouchard C, Blair SN, Haskell W. Physical activity and health (2nd ed.). Champaign: Human Kinetics; 2012.
- [11]Fitbit. Fitbit Reports $409M Q315 Revenue; Raises Guidance to $1.77 to $1.80B FY15 Revenue 2015 [cited 2016 22 January]. Available from: https://investor.fitbit.com/press/press-releases/press-release-details/2015/Fitbit-Reports-409M-Q315-Revenue-Raises-Guidance-to-177-to-180B-FY15-Revenue/default.aspx.
- [27]World Health Organization. Global recommendations on physical activity for health Geneva: World Health Organization; 2010. 26180873
- Authors
- Sushames, A., Edwards, A., Thompson, F., McDermott, R., & Gebel, K.
- Affiliations
- James Cook University (AU)
- Plymouth Marjon University (GB)
- The University of Sydney (AU)
- Corresponding author
- Sushames, Ashleigh
- Venue
- PLOS ONE
- Publisher
- Public Library of Science (PLoS)
- Published
- 2016-09-02
- Volume
- 11
- Issue
- 9
- Pages
- e0161224
- ISSN
- 1932-6203 (ISSN-L)
- PMC
- PMC5010194
- OpenAlex
- W2513449282
- Cited by
- 152
- References
- 29
- Citations by year
- 2026: 6 · 2025: 9 · 2024: 11 · 2023: 8 · 2022: 13 · 2021: 24 · 2020: 27 · 2019: 22 · 2018: 22 · 2017: 10
- FWCI
- 14.47
- Type
- journal article
- Language
- en
- Open access
- gold
- doi.org
- Licence
- Locations
- PLoS ONE (publishedVersion, cc-by)
- Europe PMC (PubMed Central) (publishedVersion, cc-by)
- PubMed Central (publishedVersion, cc-by)
- PubMed (publishedVersion)
- Create (Canterbury Christ Church University) (acceptedVersion)
- Plymouth Marjon University Repository (Plymouth Marjon University) (acceptedVersion)
- ResearchOnline at James Cook University (James Cook University) (submittedVersion)
- Research Bank (Australian Catholic University) (submittedVersion, cc-by)
- RePEc: Research Papers in Economics (submittedVersion)
- DOAJ (DOAJ: Directory of Open Access Journals) (submittedVersion, cc-by-sa)
- Funders
- College of Public Health, Medical and Veterinary Sciences
- Topics
- Health Sciences › Medicine › Physiology › Physical Activity and Health
- Physical Sciences › Computer Science › Computer Vision and Pattern Recognition › Context-Aware Activity Recognition Systems
- Health Sciences › Health Professions › General Health Professions › Mobile Health and mHealth Applications
- Keywords
- wearable activity trackers, step counting, moderate-to-vigorous physical activity, physical activity energy expenditure, ActiGraph GT3X+, measurement validity, test-retest reliability, direct observation, free-living physical activity, walking and running, stair stepping, physical activity surveillance, coefficient of variation, intraclass correlation coefficient
- MeSH terms
- Adolescent, Adult, Energy Metabolism, Female, Humans, Male, Running, Reproducibility of Results, Exercise, Walking, Monitoring, Ambulatory, Young Adult, Accelerometry
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