Methods

Fifteen professional outfield male football players, without history of lower limb injury, with at least two consecutive injury-free seasons participated. Each undertook three trials of a straight line run and sidestep cuts at 30° and 60° with approach velocity 5.5ms^-1 - 6.0ms^-1 on a FIFA (Fédération Internationale de Football Association) approved artificial football surface. Four pairs of standardised football boots (two bladed and two studded) were investigated. Using 3D inverse dynamics analyses based on an eight camera gait analysis system (120Hz) synchronised with a force platform (960Hz), peak absolute knee internal tibial rotational moments (M_z), valgus moments (M_y) and anterior joint forces (F_x) were determined throughout the stance phase. Values were compared with cadaveric critical limits for ACL injury. A univariate repeated measures ANOVA quantified differences between the variables as a function of cutting angle and boot type.