Validity of work-rate data in soccer

Problem: There was a rapid development of position detection systems in soccer during the last 10 years. These systems provide large data sets concerning the total running distances and running distances in specific speed intervals of soccer players, so called work-rate data. Based on these data, many studies have investigated the phenomenon of fatigue during a soccer match. The common procedure is to analyse the reduction of work rate data, as an indicator of fatigue. This study wanted to analyse if this method is a valid procedure to gain information about the development of fatigue during a soccer match. Method: 14 matches and 103 players of the 1. Fußball Bundesliga from the season 2009/2010 were analysed. Work-rate data was provided by a position detection system. Concerning the influence on work-rate data, variables of interest were playing position, quality of opponent, and score. Results: There was a significant influence (p<0.01) of playing position and score on the work- rate during a soccer match. For quality of opponent, a non-significant trend (p=0.067) was observed. Discussion: The results showed that there are many variables influencing the work-rate of soccer player during a match. Consequently, the analysis of the development of fatigue during a soccer match by means of the analysis of work-rate data seems to be a limited procedure. Future studies in the field of modelling fatigue should take influencing variables into account.