Peak Torque and Rotational Stiffness Developed at the Shoe-Surface Interface

Background Shoe-surface interactions have been implicated in the high number of noncontact knee injuries suffered by athletes at all levels. Purpose To examine shoe-surface interactions on newer field designs and compare these with more traditional shoe-surface combinations. The peak torque and rotational stiffness (the rate at which torque is developed under rotation) were determined. Study Design Controlled laboratory study. Methods A device was constructed to measure the torque versus applied rotation developed between different shoe-surface combinations. Data were collected on 5 different playing surfaces (natural grass, Astroturf, 2 types of Astroplay, and FieldTurf), using 2 types of shoes (grass and turf), under a compressive load of 333 N. Results The highest peak torques were developed by the grass shoe–FieldTurf tray and the turf shoe–Astroturf field combinations. The lowest peak torques were developed on the grass field. The turf shoe–Astroturf combination exhibited a rotational stiffness nearly double that of any other shoe-surface combinations. Conclusion The differences in the rotational stiffness across all 10 shoe-surface combinations were greater than those of the peak torques. It is possible that rotational stiffness may provide a new criterion for the evaluation of shoe-surface interface. Clinical Relevance An improved understanding of shoe-surface interactions remains a critical need to improve the design of shoe-surface combinations with the goal of meeting player needs while minimizing injury potential.