title: Validation of the Fitbit One activity monitor device during treadmill walking.
abstract: OBJECTIVE
  In order to quantify the effects of physical activity such as walking on chronic disease, accurate measurement of physical activity is needed. The objective of this study was to determine the validity and reliability of a new activity monitor, the Fitbit One, in a population of healthy adults.
  
  
  METHODS
  Cross-sectional study.
  
  
  METHODS
  Thirty healthy adults ambulated at 5 different speeds (0.90, 1.12, 1.33, 1.54, 1.78 m/s) on a treadmill while wearing three Fitbit One activity monitors (two on the hips and one in the pocket). The order of each speed condition was randomized. Fitbit One step count output was compared to observer counts and distance output was compared to the calibrated treadmill output. Two-way repeated measures ANOVA, concordance correlation coefficients, and Bland and Altman plots were used to assess validity and intra-class correlation coefficients (ICC) were used to assess reliability.
  
  
  RESULTS
  No significant differences were noted between Fitbit One step count outputs and observer counts, and concordance was substantial (0.97-1.00). Inter-device reliability of the step count was high for all walking speeds (ICC ≥ 0.95). Percent relative error was less than 1.3%. The distance output of the Fitbit One activity monitors was significantly different from the criterion values for each monitor at all speeds (P<0.001) and exhibited poor concordance (0.0-0.05). Inter-device reliability was excellent for all treadmill speeds (ICC ≥ 0.90). Percent relative error was high (up to 39.6%).
  
  
  CONCLUSIONS
  The Fitbit One activity monitors are valid and reliable devices for measuring step counts in healthy young adults. The distance output of the monitors is inaccurate and should be noted with caution.
authors.affiliation: Department of Physical Therapy, University of British Columbia, Canada.
authors.forename: Judit
authors.initials: J
authors.lastname: Takacs
authors.affiliation: Department of Physical Therapy, University of British Columbia, Canada.
authors.forename: Courtney L
authors.initials: CL
authors.lastname: Pollock
authors.affiliation: Department of Physical Therapy, University of British Columbia, Canada.
authors.forename: Jerrad R
authors.initials: JR
authors.lastname: Guenther
authors.affiliation: Department of Physical Therapy, University of British Columbia, Canada.
authors.forename: Mohammadreza
authors.initials: M
authors.lastname: Bahar
authors.affiliation: Department of Physical Therapy, University of British Columbia, Canada.
authors.forename: Christopher
authors.initials: C
authors.lastname: Napier
authors.affiliation: Department of Physical Therapy, University of British Columbia, Canada. Electronic address: michael.hunt@ubc.ca.
authors.forename: Michael A
authors.initials: MA
authors.lastname: Hunt
mesh_terms: D000328:Adult; D003430:Cross-Sectional Studies; D004867:Equipment Design; D005260:Female; D006801:Humans; D008297:Male; D018670:Monitoring, Ambulatory / Q000295:instrumentation*; D010809:Physical Fitness; D015203:Reproducibility of Results; D016138:Walking
keywords: Health; Pedometer; Physical activity; Reliability and validity; Walking