title: The validity of consumer-level, activity monitors in healthy adults worn in free-living conditions: a cross-sectional study.
abstract: BACKGROUND
  Technological advances have seen a burgeoning industry for accelerometer-based wearable activity monitors targeted at the consumer market. The purpose of this study was to determine the convergent validity of a selection of consumer-level accelerometer-based activity monitors.
  
  
  METHODS
  21 healthy adults wore seven consumer-level activity monitors (Fitbit One, Fitbit Zip, Jawbone UP, Misfit Shine, Nike Fuelband, Striiv Smart Pedometer and Withings Pulse) and two research-grade accelerometers/multi-sensor devices (BodyMedia SenseWear, and ActiGraph GT3X+) for 48-hours. Participants went about their daily life in free-living conditions during data collection. The validity of the consumer-level activity monitors relative to the research devices for step count, moderate to vigorous physical activity (MVPA), sleep and total daily energy expenditure (TDEE) was quantified using Bland-Altman analysis, median absolute difference and Pearson's correlation.
  
  
  RESULTS
  All consumer-level activity monitors correlated strongly (r > 0.8) with research-grade devices for step count and sleep time, but only moderately-to-strongly for TDEE (r = 0.74-0.81) and MVPA (r = 0.52-0.91). Median absolute differences were generally modest for sleep and steps (<10% of research device mean values for the majority of devices) moderate for TDEE (<30% of research device mean values), and large for MVPA (26-298%). Across the constructs examined, the Fitbit One, Fitbit Zip and Withings Pulse performed most strongly.
  
  
  CONCLUSIONS
  In free-living conditions, the consumer-level activity monitors showed strong validity for the measurement of steps and sleep duration, and moderate valid for measurement of TDEE and MVPA. Validity for each construct ranged widely between devices, with the Fitbit One, Fitbit Zip and Withings Pulse being the strongest performers.
authors.affiliation: Alliance for Research in Exercise, Nutrition and Activity (ARENA), Sansom Institute, University of South Australia, GPO Box 2471, 5001, Adelaide, Australia. ferty02f@mymail.unisa.edu.au.
authors.forename: Ty
authors.initials: T
authors.lastname: Ferguson
authors.affiliation: Alliance for Research in Exercise, Nutrition and Activity (ARENA), Sansom Institute, University of South Australia, GPO Box 2471, 5001, Adelaide, Australia. Alex.Rowlands@unisa.edu.au.
authors.forename: Alex V
authors.initials: AV
authors.lastname: Rowlands
authors.affiliation: Alliance for Research in Exercise, Nutrition and Activity (ARENA), Sansom Institute, University of South Australia, GPO Box 2471, 5001, Adelaide, Australia. tim.olds@unisa.edu.au.
authors.forename: Tim
authors.initials: T
authors.lastname: Olds
authors.affiliation: Alliance for Research in Exercise, Nutrition and Activity (ARENA), Sansom Institute, University of South Australia, GPO Box 2471, 5001, Adelaide, Australia. carol.maher@unisa.edu.au.
authors.forename: Carol
authors.initials: C
authors.lastname: Maher
mesh_terms: D061725:Accelerometry / Q000295:instrumentation*; D056044:Actigraphy / Q000295:instrumentation; D000328:Adult; D003430:Cross-Sectional Studies; D004734:Energy Metabolism; D015444:Exercise; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D018670:Monitoring, Ambulatory / Q000295:instrumentation*; D009043:Motor Activity; D015203:Reproducibility of Results; D012890:Sleep; D055815:Young Adult