New Variables and New Agreements Between 10 Hz Global Positioning System Devices in Tennis Drills

Gale ́-Ansodi C., Langarika-Rocafort A., Usabiaga O., Castellano Paulis J.

Objective:
The aim of this study was to assess the degree of agreement among repeated measurements made on the same subject using two global positioning system (GPS) devices simultaneously, focusing on the reliability of GPS devices commonly used in sports.

Methods:

Four trained male tennis players participated in the study, completing tennis-simulated point-games (n = 32).
Each player wore two GPS devices (MinimaxX v4.0; Catapult Innovations, Melbourne, Australia) simultaneously during the games.
Global indicators such as Player Load (PL), Exertion Index (EI), and Equivalent Distance Index (EDI) per minute were monitored using the GPS devices, operating at a sampling frequency of 10 Hz.
Systematic error and random error were assessed to evaluate the agreement between the measurements obtained from the two GPS devices.
Results:

Systematic error was observed, indicating that the GPS devices tended to measure variables such as mean speed (Vmean), peak speed (Vpeak), Equivalent Distance Index (EDI), PL per minute (PLmin), and EI per minute (EImin) differently.
For random error, the limit of agreement was determined. For example, in PLmin, it was found that the GPS systems would differ in 95% of cases between 2.12 and 21.42 m/min. Values outside these limits were considered relevant from a practical perspective.
The study concluded that GPS devices produced systematically different results from one another, suggesting that the bias between GPS devices should be accounted for when comparing results.
Conclusion:
The study highlights the importance of considering systematic differences between GPS devices when interpreting and comparing data. Researchers and practitioners should be aware of these biases and account for them to ensure accurate and reliable assessment of physical demands in sports.

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