title: Assessment of speed and position during human locomotion using nondifferential GPS.
abstract: OBJECTIVE
  To validate a nondifferential global positioning system (GPS) to measure speed, displacement, and position during human locomotion.
  
  
  METHODS
  Three healthy participants walked and ran over straight and curved courses for 59 and 34 trials, respectively. A nondifferential GPS receiver provided speed data by Doppler shift and change in GPS position over time, which were compared with actual speeds determined by chronometry. Displacement data from the GPS were compared with a surveyed 100-m section, and static positions were collected for 1 h and compared with the known geodetic point.
  
  
  RESULTS
  GPS speed values on the straight course were closely correlated with actual speeds (Doppler shift: r = 0.9994, P < 0.001, Delta GPS position/time: r = 0.9984, P < 0.001). Actual speed errors were lowest using the Doppler shift method (90.8% of values within +/- 0.1 m x s(-1)). Speed was slightly underestimated on a curved path, though still highly correlated with actual speed (Doppler shift: r = 0.9985, P < 0.001, Delta GPS distance/time: r = 0.9973, P < 0.001). Distance measured by GPS was 100.46 +/- 0.49 m, and 86.5% of static points were within 1.5 m of the actual geodetic point (mean error: 1.08 +/- 0.34 m, range 0.69-2.10 m).
  
  
  CONCLUSIONS
  Nondifferential GPS demonstrated a highly accurate estimation of speed across a wide range of human locomotion velocities using only the raw signal data with a minimal decrease in accuracy around bends. This high level of resolution was matched by accurate displacement and position data. Coupled with reduced size, cost, and ease of use, this method offers a valid alternative to differential GPS in the study of overground locomotion.
authors: Institute of Health and Biomedical Innovation and School of Human Movement Studies, Queensland University of Technology, Queensland, Australia.
authors: Andrew D
authors: AD
authors: Townshend
authors: Charles J
authors: CJ
authors: Worringham
authors: Ian B
authors: IB
authors: Stewart
mesh_terms: D000328:Adult; D004301:Doppler Effect; D016552:Ergometry / Q000295:instrumentation* / Q000379:methods; D005260:Female; D005684:Gait / Q000502:physiology; D006801:Humans; D008124:Locomotion / Q000502:physiology*; D008297:Male; D011187:Posture / Q000502:physiology*; D012420:Running / Q000502:physiology*; D017215:Satellite Communications / Q000295:instrumentation*; D013997:Time Factors; D016138:Walking / Q000502:physiology