Differences in Friction and Torsional Resistance in Athletic Shoe-Turf Surface Interfaces

TLDR

The study evaluated the interaction of 15 football shoes from three manufacturers in anterior translation and rotation on synthetic turf and natural grass, concluding that manufacturers should provide clear usage recommendations for specific playing surfaces. Using a pneumatic testing system, the authors measured forces under an 11.35‑kg axial load on wet and dry synthetic turf and natural grass for cleated, court, molded‑cleat, and turf shoe models. Reliability was high for translation (0.85) but moderate for rotation (0.55), wet surfaces increased rotational forces, protective taping reduced forces, and although overall grass versus AstroTurf showed no difference, cleated and turf shoes differed, with shoes used outside their intended conditions exhibiting extreme friction that could compromise safety.

Abstract

This study evaluated the shoe-surface interaction of 15 football shoes made by 3 manufacturers in both ante rior translation and rotation using a specially designed pneumatic testing system. The shoes included tradi tional cleated football shoes, "court" shoes (basketball- style shoes), molded-cleat shoes, and turf shoes. Un der an 11.35-kg (25-pound) axial load, all shoes were tested on synthetic turf under wet and dry conditions and on natural stadium grass. Test-retest reliability, as calculated using the Pearson Product-Moment Corre lation test, was 0.85 for force of translation and 0.55 for the moment of rotation. The wet versus dry surface values on translation were significantly different for rotation about the tibial axis. Spatting, which is protec tive taping of the ankle and heel applied on the outside of the shoe, resulted in a reduction of forces generated in both translation and rotation. No overall difference between shoes on grass versus AstroTurf was noted. However, there were significant differences for cleated and turf shoes. Shoes tested in conditions for which they were not designed exhibited reproducible exces sive or extreme minimal friction characteristics that may have safety implications. On the basis of this study, we urge shoe manufacturers to display sug gested indications and playing surface conditions for which their shoes are recommended.