Understanding the Effect of Changes to Natural Turf Hardness on Lower Extremity Loading

This investigation measures the biomechanical response of four soccer players (age 24 (standard deviation: 0.82) years, weight 74.6 (standard deviation: 6.9) kg, footwear size 10) to the seasonal changes that occur to a natural turf
playing surface. The surface was tested on two occasions where participants wore a pair of soccer boots with six screw-in studs (metal cleat) and a pair with 15 rubber moulded studs (moulded cleat) in a 2 × 2 surface-footwear design. While running (3.0 m/s ± 5%) and performing a 180° turn (consistent self-selected ± 5%), data were collected using Footscan pressure insoles (500 Hz, (RSscan, Belgium)). These data included peak impact force, peak impact force loading rate and the peak pressures and peak pressure loading rate at the medial and lateral heel and first and fifth metatarsals. Multiple two-way repeated measures analyses of variance were conducted on the data and p-values, effect size and confidence intervals determined. Intraclass correlation coefficients were also used to determine the reliability of data during the turning movement. Study findings demonstrate that greater pressure magnitudes were experienced
on the harder turf surfaces when running (p < 0.05) which may contribute to the greater risk of injury seen in the literature. The study results also show that the reliability of selected data collected during the 180° turning motion was good to excellent. For some measures of loading, particularly during turning, a larger confirmatory investigation is needed with sufficient statistical power to support these findings. Embargo until 01/09/2015.