The Validity and Reliability of GPS Units for Measuring Distance in Team Sport Specific Running Patterns

Jennings D., Cormack S., Coutts A.J., Boyd L., Aughey R.J.

Purpose: To assess the validity and reliability of distance data measured by global
positioning system (GPS) units sampling at 1 and 5 Hz during movement patterns
common to team sports. Methods: Twenty elite Australian Football players each
wearing two GPS devices (MinimaxX, Catapult, Australia) completed straight line
movements (10, 20, 40 m) at various speeds (walk, jog, stride, sprint), changes of
direction (COD) courses of two different frequencies (gradual and tight), and a
team sport running simulation circuit. Position and speed data were collected by the
GPS devices at 1 and 5 Hz. Distance validity was assessed using the standard error
of the estimate (±90% confidence intervals [CI]). Reliability was estimated using
typical error (TE) ± 90% CI (expressed as coefficient of variation [CV]). Results:
Measurement accuracy decreased as speed of locomotion increased in both straight
line and the COD courses. Difference between criterion and GPS measured distance
ranged from 9.0% to 32.4%. A higher sampling rate improved validity regardless
of distance and locomotion in the straight line, COD and simulated running circuit
trials. The reliability improved as distance traveled increased but decreased as speed
increased. Total distance over the simulated running circuit exhibited the lowest
variation (CV 3.6%) while sprinting over 10 m demonstrated the highest (CV
77.2% at 1 Hz). Conclusion: Current GPS systems maybe limited for assessment
of short, high speed straight line running and efforts involving change of direction.
An increased sample rate improves validity and reliability of GPS devices.