Riggio M ¹, Sassi R ², Ferrari Bravo D ², Tornaghi M ¹, Rampinini E^1,3

1, Human Performance Laboratory, MAPEI Sport Research Center, Castellanza, Varese, ITALY;2, FC Juventus, Turin, ITALY;3, Department of Sport, Nutrition and Health Sciences, Faculty of Exercise and Sports Sciences, Università degli Studi di Milano, Milan, ITALY

Global positioning systems (GPS) have been utilized to monitor and analyze the activity levels of soccer players. Despite the popularity of these systems among professional soccer teams and researchers, there is still only a small body of information investigating their validity. In this study we aimed to provide preliminary evidence on the accuracy of the SPI pro 5Hz GPS system (GPSports, Canberra, Australia) by assessing the activity profile of soccer players performing intense match phase simulations. We also examined the systems accuracy in calculating the mean metabolic power (P_mean) sustained by the athletes. Player velocities were assessed by both the GPS and a radar system (Stalker, ATS, Texas, USA). Data was collected from 8 soccer players performing 58 bouts of exercise, including sprinting, striding and jogging. The data collected by the radar system was filtered using a zero lag Butterworth filter, and the first and last 10% of the data were excluded from analysis in order to avoid the edge effect due to the filtering algorithm. Accuracy of high-intensity running (HIR >15km/h), very high-intensity running (VHIR >20km/h), total distance (TD) and P_mean of the intense match simulations were determined using the typical error (TE) expressed as a coefficient of variation. The systematic bias was also verified. Limited differences in TE were found for TD (1.0%), HIR (3.5%) and P_mean (4.6%). Whereas a notable difference was observed for VHIR (17.6%). The mean systematic bias for TD, HIR, VHIR and P_mean was -3.4%, -6.2%, -22.6% and -10.9% respectively. Based on the errors reported it appears that the GPS system can be utilized to measure TD and HIR during soccer specific activity. This is however not the case for VHIR, as the errors observed are too high to support their use. There was also a significant under-estimation for distance, as well as of the different running intensities due to systematic bias. This suggests that caution should be taken when comparing GPS data to other systems. Despite this under-estimation the Pmean value derived from the data is not impacted on excessively, and the value remains acceptable. Further studies with larger sample sizes and using 90minute soccer match simulations are necessary in order to fully validate GPS tracking systems. In addition, particular attention should be paid to the measurement of short very high-intensity movements.

The 3rd World Conference on Science and Soccer in Ghent, Belgium: 14-16 May 2012