Validity and reliability of fitbit flex for step count, moderate to vigorous physical activity and activity energy expenditure

Journal article


Sushames, A., Edwards, A., Thompson, F., McDermott, R. and Gebel, K. 2016. Validity and reliability of fitbit flex for step count, moderate to vigorous physical activity and activity energy expenditure. PLoS ONE. 11 (9). https://doi.org/10.1371/journal.pone.0161224
AuthorsSushames, A., Edwards, A., Thompson, F., McDermott, R. and Gebel, K.
Abstract

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.

Year2016
JournalPLoS ONE
Journal citation11 (9)
Digital Object Identifier (DOI)https://doi.org/10.1371/journal.pone.0161224
Publication dates
Print02 Sep 2016
Publication process dates
Deposited21 Aug 2018
Accepted02 Aug 2016
Accepted author manuscript
Output statusPublished
Additional information

Open Access. Creative Commons Attribution License 4.0

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