Validity of the Fitbit activity tracker for measuring steps in community-dwelling older adults

Serene S Paul, Anne Tiedemann, Leanne M Hassett, Elisabeth Ramsay, Catherine Kirkham, Sakina Chagpar, Catherine Sherrington, Serene S Paul, Anne Tiedemann, Leanne M Hassett, Elisabeth Ramsay, Catherine Kirkham, Sakina Chagpar, Catherine Sherrington

Abstract

Background: Commercially available activity monitors, such as the Fitbit, may encourage physical activity. However, the accuracy of the Fitbit in older adults remains unknown. This study aimed to determine (1) the criterion validity of Fitbit step counts compared to visual count and ActiGraph accelerometer step counts and (2) the accuracy of ActiGraph step counts compared to visual count in community-dwelling older people.

Methods: Thirty-two community-dwelling adults aged over 60 wore Fitbit and ActiGraph devices simultaneously during a 2 min walk test (2MWT) and then during waking hours over a 7-day period. A physiotherapist counted the steps taken during the 2MWT.

Results: There was excellent agreement between Fitbit and visually counted steps (intraclass correlation coefficient (ICC2,1)=0.88, 95% CI 0.76 to 0.94) from the 2MWT, and good agreement between Fitbit and ActiGraph (ICC2,1=0.66, 95% CI 0.41 to 0.82), and between ActiGraph and visually counted steps (ICC2,1=0.60, 95% CI 0.33 to 0.79). There was excellent agreement between the Fitbit and ActiGraph in average steps/day over 7 days (ICC2,1=0.94, 95% CI 0.88 to 0.97). Percentage agreement was closest for Fitbit steps compared to visual count (mean 0%, SD 4%) and least for Fitbit average steps/day compared to the ActiGraph (mean 13%, SD 25%).

Conclusions: The Fitbit accurately tracked steps during the 2MWT, but the ActiGraph appeared to underestimate steps. There was strong agreement between Fitbit and ActiGraph counted steps. The Fitbit tracker is sufficiently accurate to be used among community-dwelling older adults to monitor and give feedback on step counts.

Keywords: accelerometer; aged; pedometer; physical activity; validity.

Figures

Figure 1
Figure 1
Bland-Altman plots comparing step counts over a 2 min walk test for the Fitbit tracker, ActiGraph accelerometer and visual count by a physiotherapist. (A) Comparison between the Fitbit tracker and visual count. (B) Comparison between the Fitbit tracker and ActiGraph accelerometer. (C) Comparison between the ActiGraph accelerometer and visual count. Actigraph_2MWT: ActiGraph step counts from the 2 min walk test. Fitbit_2MWT: Fitbit step counts from the 2 min walk test. Visual_2MWT: Physiotherapist-counted steps from the 2 min walk test. Solid line indicates the mean difference between the two measures, dashed lines indicate the limits of agreement (1.96 SDs of the mean difference).
Figure 2
Figure 2
Bland-Altman plot comparing average steps/day over a 7-day period for the Fitbit tracker and ActiGraph accelerometer. Fitbit_week: Fitbit average steps/day from a 7-day period. Actigraph_week: ActiGraph average steps/day from a 7-day period. Solid line indicates the mean difference between the two measures, dashed lines indicate the limits of agreement (1.96 SDs of the mean difference).

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