Effects of Synthetic Turf Systems With and Without a Shock Pad on Lower Extremity Biomechanics During a 90° Cutting Movement With Differing Approach Velocities

The purpose of this study was to examine differences in lower extremity kinematics and kinetics on two different synthetic turf systems (turf only and turf with a shock pad) for two approach velocities (3.0 and 4.0 m/s) during a 90° cutting movement. Twelve recreational male American football and soccer players were recruited to perform five trials for each of the four conditions. A three-dimensional motion analysis system synchronized to a force platform was used to collect marker coordinate and ground reaction force (GRF) data respectively. A 2 x 2 (surface x approach velocity) ANOVA was used to analyze kinematic and kinetic variables. Across surface conditions, there was a general lack of significant differences. While there was a lack of differences for kinematics and kinetics, there might have been increased co-contractions to stabilize the lower extremity with the increased deformation on the shock pad condition, which was undetectable via the inverse dynamics. However, knee frontal-plane peak loading eccentric power was found to be greater on the shock pad condition (p = 0.013) while knee frontal-plane peak push-off eccentric power was reduced on the shock pad condition (p = 0.020). A surface x approach velocity interaction was detected for knee sagittal-plane peak eccentric power (p = 0.018). Post-hoc analysis found a significant difference for approach velocity on the turf only condition. As the protocol dictated a change in performance, the largest changes were seen in peak hip extension (p = 0.007) and knee extension (p = 0.004) moments, suggesting that these were the major factors for determining the performance improvement. There were also increases in ankle eversion moment (p < 0.001) and ankle inversion ROM (p = 0.001) as approach velocity increased. These increases potentially suggest that the risk of a lateral ankle sprain injury increases as approach velocity increases. As approach velocity increased, it was found that peak push-off vertical GRF decreased (p = 0.011) as peak push-off medial GRF increased (p = 0.025). This suggests that as approach velocity increases, medial forces become more important than vertical forces during the push-off phase.