GPS isn't just for guiding confused drivers, it can also be used by soccer managers who are a little lost when it comes to assessing their players' performance. Acceleration, average and maximum speed, distance covered, etc. "It allows us to know the displacements of the players in a valid, reliable and effective way," says David Casamichana. This researcher has in fact completed a thesis in which he demonstrates the applicability and good results of GPS in soccer, and specifically of the model available at the Faculty of Physical Activity and Sports Sciences at the University of the Basque Country (UPV/EHU).

The title of his work is La tecnología GPS aplicada a la evaluación del entrenamiento y la competición en fútbol (GPS technology applied to assessing training and competition in soccer) and has led to the publication of various papers including one he highlights in the Journal of Sports Science.

The GPS model validated in this paper is the MinimaxX v.4.0, which emits a 10 Hz sampling frequency; in other words, it provides ten data per second on the position of the player wearing the device. In fact, the Department of Physical and Sports Education opted for it because, at the time, it was the one that offered the highest sampling frequency. "The early devices marketed provided one datum per second. In that case, if you move and return to your starting point in a rapid displacement, the system will understand that you have not moved," explains Casamichana. Logically, the validity and reliability of a GPS device increases as the sampling frequency increases, but it needed to be demonstrated, since there were no validity studies for this particular model. In actual fact, this piece of research has tested its high level of accuracy, which even in fast races of 15 metres offers results of a moderate to high validity.

Acceleration as an indicator

In this study, Casamichana worked with players in the Rayo Cantabria de Santander soccer team (a semi-professional Spanish third-division team), who used GPS devices in training sessions and in friendly matches. "FIFA bans their use in competitions, so that they can't put the least able players at a disadvantage; that is why we can only try out the system in the friendly matches," he explains.

He has not only confirmed the accuracy of the GPS device itself, but also that of the workload indicators obtained through using it. Workload indicators are a series of figures that should represent the physical condition of the player during moments of exertion and which are used so that managers can evaluate their soccer players. For example, a good indicator could come from the total distance covered during training, or from any datum that reflects fatigue level. The quantifying of the indicators by means of GPS has produced satisfactory results. But the fact is, the indicator obtained through an accelerometer fitted to the device has also been validated, and this is something that the PhD tribunal regarded as a highly positive aspect. "One of the members of the tribunal told me that, as far as he was concerned, the most important aspect of the thesis was the new path that had been opened up whereby the distances covered were no longer studied, and the accelerations made by the sportspeople were the focus instead," says Casamichana.

Profile according to position

Having confirmed the validity of the system and the methodology, the research includes interesting information obtained during the study, such as the physical profile of the players according to their position on the field. On the basis of the data gathered, Casamichana explains that centre backs and centre forwards are the ones that run the least distance, unlike the midfielders. As for the distance covered in the sprint, the midfielders are in fact the ones who come last. In the band in which most of the sprints take place, the midfielders come top in terms of number of accelerations and high intensity movements.

The study also includes a comparison between training sessions and friendly matches; the values are higher in the latter in all the variables analysed, except the distance covered at low intensity. Among other things, during the matches the players cover a greater total distance per minute, at a greater speed, and the sprints are more frequent and longer.