title: Concurrent Validity of GPS for Deriving Mechanical Properties of Sprint Acceleration.
abstract: OBJECTIVE
  To test the concurrent validity of data from 2 different global positioning system (GPS) units for obtaining mechanical properties during sprint acceleration using a field method recently validated by Samozino et al.
  
  
  METHODS
  Thirty-two athletes performed maximal straight-line sprints, and their running speed was simultaneously measured by GPS units (sampling rate: 20 or 5 Hz) and either a radar or laser device (devices taken as references). Lower-limb mechanical properties of sprint acceleration (theoretical maximal force, theoretical maximal speed, maximal power) were derived from a modeling of the speed-time curves using an exponential function in both measurements. Comparisons of mechanical properties from 20- and 5-Hz GPS units with those from reference devices were performed for 80 and 62 trials, respectively.
  
  
  RESULTS
  The percentage bias showed a wide range of overestimation or underestimation for both systems (-7.9% to 9.7% and -5.1% to 2.9% for 20- and 5-Hz GPS), while the ranges of its 90% confidence limits for 20-Hz GPS were markedly smaller than those for 5-Hz GPS. These results were supported by the correlation analyses.
  
  
  CONCLUSIONS
  Overall, the concurrent validity for all variables derived from 20-Hz GPS measurements was better than that obtained from the 5-Hz GPS units. However, in the current state of GPS devices' accuracy for speed-time measurements over a maximal sprint acceleration, it is recommended that radar, laser devices, and timing gates remain the reference methods for implementing the computations of Samozino et al.
authors.forename: Ryu
authors.initials: R
authors.lastname: Nagahara
authors.forename: Alberto
authors.initials: A
authors.lastname: Botter
authors.forename: Enrico
authors.initials: E
authors.lastname: Rejc
authors.forename: Masaaki
authors.initials: M
authors.lastname: Koido
authors.forename: Takeshi
authors.initials: T
authors.lastname: Shimizu
authors.forename: Pierre
authors.initials: P
authors.lastname: Samozino
authors.forename: Jean-Benoit
authors.initials: JB
authors.lastname: Morin
mesh_terms: D000054:Acceleration; D001696:Biomechanical Phenomena; D005538:Football / Q000502:physiology; D040362:Geographic Information Systems; D006801:Humans; D035002:Lower Extremity / Q000502:physiology; D008297:Male; D015203:Reproducibility of Results; D012420:Running / Q000502:physiology*; D012916:Soccer / Q000502:physiology; D013647:Task Performance and Analysis; D055815:Young Adult
keywords: force; laser; power; running; velocity