The effects of forefoot bending stiffness in athletic footwear on stresses in the second metatarsal

High forefoot bending stiffness has become a common feature in road running shoes worn by athletes seeking to improve performance. The consensus throughout the literature is that increased forefoot bending stiffness in running shoes can enhance performance. However, the injury implications of running in shoes with high forefoot bending stiffness are not well understood. Second metatarsal (MT2) stress fractures are common in long-distance runners due to high repetitive loading. Changes in pressure magnitudes and patterns during locomotion may contribute to greater MT2 stress and therefore increase forefoot injury risk. Therefore, this study aimed to determine the isolated influence of forefoot bending stiffness in athletic footwear on MT2 stress and lower limb biomechanics during running. Synchronised force and kinematic data were collected during overground running (3.6 ms−1) from 13 female participants in three different shoe conditions (Normal, High and Low stiffness). Peak MT2 compressive and tensile stresses were estimated using a 2D beam theory model. In the High stiffness shoe peak compressive and tensile stress increased compared to the Normal and Low stiffness shoes (p = 0.001, d = 0.6). Peak MT2 pressure (p < 0.001, d = 0.5) was also higher in the High shoe condition, with no differences between Normal and Low conditions (p > 0.05). These findings suggest that large magnitudes of forefoot bending stiffness in running shoes can increase mechanical load on the structures of the forefoot compared with conventional stiffness shoes, potentially increasing MT2 injury risk in runners who choose to wear such shoes.