Teeter-totter effect: a new mechanism to understand shoe-related improvements in long-distance running
Benno M. Nigg, Saša Čigoja, Sandro Nigg
Abstract
The effect of shoe mid-sole construction on running performance was discussed with reference to the Nike Vaporfly 4%.1 Drs Burns and Tam described the mid-sole thickness as the major running shoe characteristic that contributes to changes in performance. Here, we highlight the role of the curved carbon fibre plate embedded in the mid-sole, and introduce a new effect on running mechanics, the ‘ teeter-totter effect ’. During ground contact in running, the point of application of the ground reaction force moves anteriorly during the second half of ground contact towards the front end of the curved carbon fibre plate. We suggest that, in this position, the ground reaction force produces a ‘reaction’ force at the heel in upward direction (perpendicular to the direction of the plate; figure 1). Figure 1 Schematic illustration of the teeter-totter effect including the application point of the ground reaction force (red full circle) and its translation (red broken circle and line), the applied force of the runner (black arrow) at the front part of the shoe and the reaction force at the heel of the foot (red arrow) during early/mid-stance (left orientation) and push-off (right orientation). Image modified from nike.com. If the curvature of the plate is designed correctly, the teeter-totter effect …