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

doi:10.1136/bmjsem-2015-000013

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

BMJ Open Sport Exerc Med. 2015 Jul 8;1(1):e000013. doi: 10.1136/bmjsem-2015-000013. eCollection 2015.

Authors

Serene S Paul¹, Anne Tiedemann¹, Leanne M Hassett², Elisabeth Ramsay¹, Catherine Kirkham¹, Sakina Chagpar¹, Catherine Sherrington¹

Affiliations

¹ The George Institute for Global Health, Sydney Medical School, The University of Sydney , Sydney, New South Wales , Australia.
² The George Institute for Global Health, Sydney Medical School, The University of Sydney, Sydney, New South Wales, Australia; Faculty of Health Sciences, The University of Sydney, Sydney, New South Wales, Australia.

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 (ICC_2,1)=0.88, 95% CI 0.76 to 0.94) from the 2MWT, and good agreement between Fitbit and ActiGraph (ICC_2,1=0.66, 95% CI 0.41 to 0.82), and between ActiGraph and visually counted steps (ICC_2,1=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 (ICC_2,1=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.