Concurrent validity of GPS for deriving mechanical properties of sprint acceleration

Purpose: The purpose of this study was to test the concurrent validity of data from two 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 Hz or 5 Hz) and either a radar or laser device (devices taken as references). Lower limb mechanical properties of sprint acceleration (theoretical maximal force, F0; theoretical maximal speed, V0; maximal power, Pmax) were derived from a modeling of the speed-time curves using an exponential function in both measurements. Comparisons of mechanical properties from 20 Hz 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 over or underestimation for both systems (-7.9-9.7% and -5.1-2.9% for 20 Hz 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, we recommend that radar, laser devices and timing gates remain the reference methods for implementing Samozino et al.'s computations.