Background: 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.
Results: 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(®).
Conclusions: 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(®).
Keywords: Accelerometer; Energy expenditure; Fitbit; Physical activity; Validation studies; Walking.