Validation of the Fitbit One® for physical activity measurement at an upper torso attachment site

Keith M. Diaz, David J. Krupka, Melinda J. Chang, Jonathan A. Shaffer, Yao Ma, Jeff Goldsmith, Joseph E. Schwartz, Karina W. Davidson

The upper torso is recommended as an attachment site for the Fitbit One(®), one of the most common wireless physical activity trackers in the consumer market, and could represent a viable alternative to wrist- and hip-attachment sites. The objective of this study was to provide evidence concerning the validity of the Fitbit One(®) attached to the upper torso for measuring step counts and energy expenditure among female adults. Thirteen female adults completed a four-phase treadmill exercise protocol (1.9, 3.0, 4.0, and 5.2 mph). Participants were fitted with three Fitbit(®) trackers (two Fitbit One(®) trackers: one on the upper torso, one on the hip; and a wrist-based Fitbit Flex(®)). Steps were assessed by manual counting of a video recording. Energy expenditure was measured by gas exchange indirect calorimetry. Concordance correlation coefficients of Fitbit-estimated step counts to observed step counts for the upper torso-attached Fitbit One(®), hip-attached Fitbit One(®) and wrist-attached Fitbit Flex(®) were 0.98 (95 % CI 0.97-0.99), 0.99 (95 % CI 0.99-0.99), and 0.75 (95 % CI 0.70-0.79), respectively. The percent error for step count estimates from the upper torso attachment site was ≤3 % for all walking and running speeds. Upper torso step count estimates showed similar accuracy relative to hip attachment of the Fitbit One(®) and were more accurate than the wrist-based Fitbit Flex(®). Similar results were obtained for energy expenditure estimates. Energy expenditure estimates for the upper torso attachment site yielded relative percent errors that ranged from 9 to 19 % and were more accurate than the wrist-based Fitbit Flex(®), but less accurate than hip attachment of the Fitbit One(®). Our study shows that physical activity measures obtained from the upper torso attachment site of the Fitbit One(®) are accurate across different walking and running speeds in female adults. The upper torso attachment site of the Fitbit One(®) outperformed the wrist-based Fitbit Flex(®) and yielded similar step count estimates to hip-attachment. These data support the upper torso as an alternative attachment site for the Fitbit One(®).