title: The inter- and intra-unit variability of a low-cost GPS data logger/receiver to study human outdoor walking in view of health and clinical studies.
abstract: OBJECTIVE
  The present study evaluates the intra- and inter-unit variability of the GlobalSat® DG100 GPS data logger/receiver (DG100) when estimating outdoor walking distances and speeds.
  
  
  METHODS
  Two experiments were performed using healthy subjects walking on a 400 m outdoor synthetic track. The two experiments consisted of two different outdoor prescribed walking protocols with distances ranging from 50 to 400 m. Experiment 1 examined the intra-unit variability of the DG100 (test-retest reproducibility) when estimating walking distances. Experiment 2 examined the inter-unit variability of four DG100 devices (unit to unit variability) when estimating walking distances and speeds.
  
  
  RESULTS
  The coefficient of variation [95% confidence interval], for the reliability of estimating walking distances, was 2.8 [2.5-3.2] %. The inter-unit variability among the four DG100 units tested ranged from 2.8 [2.5-3.2] % to 3.9 [3.5-4.4] % when estimating distances and from 2.7 [2.4-3.0] % to 3.8 [3.4-4.2] % when estimating speeds.
  
  
  CONCLUSIONS
  The present study indicates that the DG100, an economical and convenient GPS data logger/receiver, can be reliably used to study human outdoor walking activities in unobstructed conditions. This device let facilitate the use of GPS in studies of health and disease.
authors.affiliation: Laboratory of Vascular Investigations and Sports Medicine, University Hospital, Angers, France.
authors.forename: Pierre
authors.initials: P
authors.lastname: Abraham
authors.forename: Bénédicte
authors.initials: B
authors.lastname: Noury-Desvaux
authors.forename: Marie
authors.initials: M
authors.lastname: Gernigon
authors.forename: Guillaume
authors.initials: G
authors.lastname: Mahé
authors.forename: Thomas
authors.initials: T
authors.lastname: Sauvaget
authors.forename: Georges
authors.initials: G
authors.lastname: Leftheriotis
authors.forename: Alexis
authors.initials: A
authors.lastname: Le Faucheur
mesh_terms: D000328:Adult; D003365:Costs and Cost Analysis; D005260:Female; D040362:Geographic Information Systems / Q000191:economics* / Q000295:instrumentation*; D006262:Health; D006801:Humans; D008297:Male; D018670:Monitoring, Ambulatory / Q000191:economics* / Q000295:instrumentation*; D012146:Rest; D016138:Walking / Q000502:physiology*