Peak torque and rotational stiffness developed at the shoe-surface interface: the effect of shoe type and playing surface.

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.