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BMJ Open Sport Exerc Med. 2017 Sep 13;3(1):e000254. doi: 10.1136/bmjsem-2017-000254. eCollection 2017.

Validity of Fitbit's active minutes as compared with a research-grade accelerometer and self-reported measures.

Author information

1
School of Physical Therapy, Texas Woman's University, Institute of Health Sciences-Houston, Houston, Texas, USA.
2
School of Physical Therapy, University of New England, Portland, Maine, USA.

Abstract

OBJECTIVES:

The main purpose of the study was to assess the validity between the Fitbit and ActiGraph GT3X+ accelerometer. The specific aims were to determine the: (1) concurrent validity between the various models of the Fitbit and the GTX3+ accelerometer as the criterion measure for: number of steps and active minutes averaged over a single-day and 7-day period; (2) validity of the two devices with the International Physical Activity Questionnaire (IPAQ) for the number of daily active minutes performed.

METHODS:

Fifty-three subjects wore a Fitbit and ActiGraph concurrently for 7 days. Data were analysed using correlation coefficients, t-tests to assess mean comparisons and Bland-Altman plots to determine agreement between the Fitbit and the ActiGraph.

RESULTS:

The correlations between the Fitbit and ActiGraph for steps per day and per 7 days were r=0.862 and 0.820, respectively with significant mean differences between both devices. Bland-Altman analyses revealed agreement between the Fitbit and the ActiGraph for 7-day active minutes only. The correlations between the Fitbit and ActiGraph for active minutes per day and per 7 days were r=0.695 and r=0.658, respectively, with no significant mean differences between both devices. No significant correlations were found between the IPAQ and the other two devices.

CONCLUSIONS:

The data produced by the Fitbit were consistent with the ActiGraph when the means of each device were compared over the 1-day and 7-day time periods. However, Bland-Altman analyses revealed that the Fitbit agreed with the ActiGraph when used to measure physical activity levels over a 7-day span only.

KEYWORDS:

Physical activity; accelerometer; tracker; validity

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