Three dimensional analysis of knee biomechanics when landing on natural turf and football turf

In 2004, Fédération Internationale de Football Association (FIFA) officially recognized artificial turf (football turf) as an appropriate playing surface for competitive football, although surface suitability remains relatively unknown and in particular, player testing of new surfaces is under-reported. The present study was designed with two aims: to examine knee joint angle precision of measurement and to investigate whether knee kinematics varied when landing from a jump on football turf (FT) and natural turf (NT). A series of static reference positions were compared for two series of repeated stationary measures and three dimensional (3D) knee joint angles used to assess intra- and inter-trial reliability. In addition, to eliminate marker placement variability, a single subject design was used to compare 20 jump landings following a heading movement performed on FT and 20 on NT in a randomized fashion. A single-step approach into a jump to head a stationary suspended football was followed by a single-leg landing on FT or NT and a two-step forward sprint. The turfs were mounted on a force plate (Kistler) and 3D kinematic data collected for all trials using an automated motion analysis system (CODA motion) utilizing cluster markers. Results showed reliability across reference positions and between most trials of ∼1°. Observed differences highlighted the importance of initial static trial reference positions. For the turf landing trials, similar knee flexion/extension and internal/external rotation angles throughout the contact phase were seen, whilst differences occurred in knee adduction/abduction angles. Greater movement variability was demonstrated in all three knee joint angles under FT compared to NT. Such differences could be exaggerated during more dynamic football movements and may have performance and injury implications that warrant further investigation.