title: Validity and reliability of Fitbit activity monitors compared to ActiGraph GT3X+ with female adults in a free-living environment.
abstract: OBJECTIVE
  Inexpensive activity monitors have recently gained popularity with the general public. Researchers have evaluated these consumer-based monitors in laboratory-conditions. Given the current wide-spread consumer use of these devices, it is important to ensure users are attaining accurate information compared to previously validated measures. This study investigates the accuracy of Fitbit One and Flex activity monitors in measuring steps, sedentary time, and time spent in light, moderate, and vigorous intensity activities with ActiGraph GT3X+ with female adults in free-living conditions.
  
  
  METHODS
  Cross-sectional study.
  
  
  METHODS
  Twenty-two women, 21.23±1.63 years, BMI: 22.35±2.34kg/m2wore two Fitbit Ones (bra and waist), one Fitbit Flex on the wrist, and one ActiGraph GT3X+ on the waist for seven-consecutive days. Repeated measures ANOVA was used to explore differences in steps, sedentary time, and time spent in light, moderate and vigorous intensity activities among the four devices.
  
  
  RESULTS
  No differences were found in number of steps recorded across the four devices. Fitbit One, waist and bra, overestimated time spent in light intensity activities. Fitbit One (waist) and Fitbit Flex overestimated time spent in moderate intensity activities. Fitbit One, waist and bra, and Fitbit Flex overestimated time spent in vigorous intensity activities. All Fitbit activity monitors overestimated MVPA and underestimated sedentary time compared to the ActiGraph.
  
  
  CONCLUSIONS
  Regardless of wear-location all Fitbit devices provide similar activity monitoring and users can wear the devices wherever best accommodates their lifestyle or needs. Users should not rely solely on these monitors when tracking vigorous and MVPA activities.
authors.affiliation: McGill University, Department of Kinesiology and Physical Education, Montreal, Quebec, Canada. Electronic address: ryan.reid@mail.mcgill.ca.
authors.forename: Ryan E R
authors.initials: RER
authors.lastname: Reid
authors.affiliation: McGill University, Department of Kinesiology and Physical Education, Montreal, Quebec, Canada.
authors.forename: Jessica A
authors.initials: JA
authors.lastname: Insogna
authors.affiliation: McGill University, Department of Kinesiology and Physical Education, Montreal, Quebec, Canada.
authors.forename: Tamara E
authors.initials: TE
authors.lastname: Carver
authors.affiliation: McGill University, Department of Kinesiology and Physical Education, Montreal, Quebec, Canada.
authors.forename: Andrea M
authors.initials: AM
authors.lastname: Comptour
authors.affiliation: McGill University, Department of Kinesiology and Physical Education, Montreal, Quebec, Canada.
authors.forename: Nicole A
authors.initials: NA
authors.lastname: Bewski
authors.affiliation: McGill University, Department of Kinesiology and Physical Education, Montreal, Quebec, Canada.
authors.forename: Cristina
authors.initials: C
authors.lastname: Sciortino
authors.affiliation: McGill University, Department of Kinesiology and Physical Education, Montreal, Quebec, Canada.
authors.forename: Ross E
authors.initials: RE
authors.lastname: Andersen
mesh_terms: D056044:Actigraphy / Q000295:instrumentation*; D000328:Adult; D000704:Analysis of Variance; D003430:Cross-Sectional Studies; D005260:Female; D006801:Humans; D057187:Independent Living; D018670:Monitoring, Ambulatory / Q000295:instrumentation*; D015203:Reproducibility of Results
keywords: Fitbit; Physical activity; Reliability; Sedentary behavior; Validation