title: Comparison of home and away-from-home physical activity using accelerometers and cellular network-based tracking devices.
abstract: BACKGROUND
  Measuring physical at home and away from home is essential for assessing health and well-being, and could help design interventions to increase physical activity. Here, we describe how physical activity at home and away from home can be quantified by combining information from cellular network-based tracking devices and accelerometers.
  
  
  METHODS
  Thirty-five working adults wore a cellular network-based tracking device and an accelerometer for 6 consecutive days and logged their travel away from home. Performance of the tracking device was determined using the travel log for reference. Tracking device and accelerometer data were merged to compare physical activity at home and away from home.
  
  
  RESULTS
  The tracking device detected 98.6% of all away-from-home excursions, accurately measured time away from home and demonstrated few prolonged signal drop-out periods. Most physical activity took place away from home on weekdays, but not on weekends. Subjects were more physically active per unit of time while away from home, particularly on weekends.
  
  
  CONCLUSIONS
  Cellular network-based tracking devices represent an alternative to global positioning systems for tracking location, and provide information easily integrated with accelerometers to determine where physical activity takes place. Promoting greater time spent away from home may increase physical activity.
authors.affiliation: Wilmer Eye Institute, Johns Hopkins University, Baltimore, MD, USA.
authors.forename: Pradeep Y
authors.initials: PY
authors.lastname: Ramulu
authors.forename: Emilie S
authors.initials: ES
authors.lastname: Chan
authors.forename: Tara L
authors.initials: TL
authors.lastname: Loyd
authors.forename: Luigi
authors.initials: L
authors.lastname: Ferrucci
authors.forename: David S
authors.initials: DS
authors.lastname: Friedman
mesh_terms: D061725:Accelerometry / Q000706:statistics & numerical data*; D000293:Adolescent; D000328:Adult; D015444:Exercise; D005260:Female; D040362:Geographic Information Systems / Q000706:statistics & numerical data*; D006801:Humans; D008297:Male; D008875:Middle Aged; D013997:Time Factors; D055815:Young Adult