Monitoring fatigue-induced ground reaction forces variations among professional football players using an instrumented pair of football shoes: a two-phase study

Fatigue has been identified as a major injury risk factor in football due to the increasing number of muscle injuries occurring at the end of matches and during congested weeks of training. Fatigue is known for affecting kinetic (i.e. ground reaction forces – GRF), kinematic and spatio-temporal parameters during running/playing football. Consequently, a lot of authors have studied the evolution of these parameters in a fatigue state to gain more insights into players’ fatigue and fitness levels, leading to conflicting results. This lack of consensus could be due to the current lack of device to measure on-field GRF, leading to poor ecological validity. The recent development and validation of an instrumented pair of football shoes capable of measuring GRF in situ (i.e. on a football turf) could therefore represents a breakthrough. Consequently, the two aims of this study were i) to assess fatigue-induced GRF parameters variations during an exhaustive run performed by amateur football players and ii) to longitudinally monitor these variations during an entire competitive season among professional football players. Results demonstrated some significant variations among amateur football players between the beginning and the end of the exhaustive run. Results from the longitudinal study also demonstrated some large and significant changes among professional football players GRF parameters throughout the season, thus confirming the potential of this device to quantify biomechanical fatigue of professional players. This technology could thus be used by practitioners, in association with traditional training load monitoring tools, to better estimate players’ fatigue and fitness.