Effects of Shock Pad and Synthetic Turf on Ankle Biomechanics in a 90° Cutting Movement

Abstract

Shock pad (PAD) is a popular choice underlayment installed under a synthetic turf (TURF) field. The effects of PAD on impact attenuation and injury risks of human movements are still relatively unknown. PURPOSE: To examine impact attenuation related ankle biomechanical characteristics of a 90° cutting movement on synthetic turf with shock pad compared to synthetic turf only. METHODS: Twelve recreational football and soccer players performed five successful trials of 90° cutting movement in each of two approaching speed conditions: 3.0±0.3 (SLOW) and 4.0±0.4 (FAST) m/s on each of TURF and PAD surface conditions. Three-dimensional kinematic and ground reaction force (GRF) data were collected simultaneously. A 2” monofilament synthetic turf with 1/2” stitch gauge was used in TURF and PAD conditions. A foam-based shock pad was used in PAD condition. RESULTS: No significant surface main effect or surface by speed interactions were found for any ankle kinematic and kinetic variables and peak GRFs (p > 0.05). Increased peak ankle eversion moment (0.65 vs. 0.84 Nm/kg, p<0.001) and inversion loading range of motion (ROM, 13.7 vs. 18.6 deg, p=0.001) were seen in FAST compared to SLOW. Increases for peak ankle sagittal-plane concentric pushoff power, and frontal-plane eccentric and concentric power were also observed in FAST compared to SLOW. Peak vertical (2.04 vs. 2.31 BW, p=0.023) and medial loading (0.79 vs. 1.11 BW, p=0.002) GRFs were higher in FAST than SLOW. Additionally, peak pushoff medial GRFs were increased from SLOW to FAST (0.91 vs. 1.20 BW, p=0.025), but pushoff vertical GRFs were decreased slightly (2.24 vs. 2.11 BW, p=0.011). CONCLUSIONS: The lack of significant differences between TURF and PAD and their interactions for examined ankle and GRF variables suggest that adding a form-based shock pad does not impede cutting performance. These results also seem to indicate there is a neuromuscular accommodation in cutting mechanics on PAD surface, which cannot be reflected loading variables using inverse dynamics. As cutting speed increased, greater increases in medial peak GRFs, and frontal-plane peak ankle moment and ROM were observed compared to those in sagittal-plane, suggesting increased mediolateral loading to ankle complex in fast cut movement. Supported in part by Brock International.