Biomechanical responses to changes in friction on a clay court surface

To examine the influence of clay court frictional properties on tennis players' biomechanical response.

Repeated measures.

Lower limb kinematic and force data were collected on sixteen university tennis players during 10×180° turns (running approach speed 3.9±0.20ms^-1) on a synthetic clay surface of varying friction levels. To adjust friction levels the volume of sand infill above the force plate was altered (kg per m² surface area; 12, 16 and 20kgm^-2). Repeated measures ANOVA and Bonferroni's corrected alpha post-hoc analyses were conducted to identify significant differences in lower limb biomechanics between friction levels.

Greater sliding distances (η_p²=0.355, p=0.008) were observed for the lowest friction condition (20kgm^-2) compared to the 12 and 16kgm^-2 conditions. No differences in ankle joint kinematics and knee flexion angles were observed. Later peak knee flexion occurred on the 20kgm^-2 condition compared to the 12kgm^-2 (η_p²=0.270, p=0.023). Lower vertical (η_p²=0.345, p=0.027) and shear (η_p²=0.396, p=0.016) loading rates occurred for the 20kgm² condition compared to the 16kgm².

Lower loading rates and greater sliding distances when clay surface friction was reduced suggests load was more evenly distributed over time reducing players' injury risks. The greater sliding distances reported were accompanied with later occurrence of peak knee flexion, suggesting longer time spent braking and a greater requirement for muscular control increasing the likelihood of fatigue.