Forefoot bending stiffness of cleated American football shoes

Abstract

In American football, hyper-dorsiflexion of the first metatarsophalangeal (1 MTP) joint is the predominant mechanism of 1 MTP sprains (turf toe). The risk of acute 1 MTP sprain has been found to increase as 1 MTP angle increases. The bending resistance of the shoe dictates the proportion of an externally applied load that can be passed into the shoe (i.e., not through the 1 MTP joint) and thus influences the magnitude of flexion imparted to the 1 MTP joint. This study quantified the forefoot bending resistance of a range of cleated American football shoes. A total of 21 pairs of size 12 shoes were dynamically tested over flexion angles from 30° to 90°. Bending stiffness ranged from 0.10 to 0.35 Nm/deg, while peak torque ranged from 5.1 to 16.6 Nm. The relationship between torque and flexion angle was nearly linear for all of the shoes tested and the peak torque values were substantially lower than 1 MTP joint moments that have been measured in the human foot during athletic activities. These results suggest that an opportunity exists to better balance athletic performance and acute 1 MTP joint injury risk by incorporating non-linearity into the torque-angle characteristic of football cleats, such that the proportion of external load borne by the shoe increases at flexion angles above 60°.