title: Validity of the Apple iPhone® /iPod Touch® as an accelerometer-based physical activity monitor: a proof-of-concept study.
abstract: BACKGROUND
  The popularity of smartphones has led researchers to ask if they can replace traditional tools for assessing free-living physical activity. Our purpose was to establish proof-of-concept that a smartphone could record acceleration during physical activity, and those data could be modeled to predict activity type (walking or running), speed (km·h-1), and energy expenditure (METs).
  
  
  METHODS
  An application to record and e-mail accelerations was developed for the Apple iPhone®/iPod Touch®. Twenty-five healthy adults performed treadmill walking (4.0 km·h-1 to 7.2 km·h-1) and running (8.1 km·h-1 to 11.3 km·h-1) wearing the device. Criterion energy expenditure measurements were collected via metabolic cart.
  
  
  RESULTS
  Activity type was classified with 99% accuracy. Speed was predicted with a bias of 0.02 km·h-1 (SEE: 0.57 km·h-1) for walking, -0.03 km·h-1 (SEE: 1.02 km·h-1) for running. Energy expenditure was predicted with a bias of 0.35 METs (SEE: 0.75 METs) for walking, -0.43 METs (SEE: 1.24 METs) for running.
  
  
  CONCLUSIONS
  Our results suggest that an iPhone/iPod Touch can predict aspects of locomotion with accuracy similar to other accelerometer-based tools. Future studies may leverage this and the additional features of smartphones to improve data collection and compliance.
authors.affiliation: Faculty of Kinesiology, University of Calgary, Calgary, Alberta, Canada.
authors.forename: Meaghan
authors.initials: M
authors.lastname: Nolan
authors.forename: J Ross
authors.initials: JR
authors.lastname: Mitchell
authors.forename: Patricia K
authors.initials: PK
authors.lastname: Doyle-Baker
mesh_terms: D061725:Accelerometry / Q000295:instrumentation* / Q000379:methods / Q000592:standards; D000328:Adult; D000416:Alberta; D000704:Analysis of Variance; D015992:Body Mass Index; D004734:Energy Metabolism / Q000502:physiology*; D005080:Exercise Test / Q000295:instrumentation; D005260:Female; D006339:Heart Rate / Q000502:physiology*; D006801:Humans; D016015:Logistic Models; D055539:MP3-Player; D008297:Male; D008991:Monitoring, Physiologic / Q000295:instrumentation* / Q000379:methods / Q000592:standards; D012420:Running / Q000502:physiology*; D012984:Software; D016138:Walking / Q000502:physiology*