In a recent article published in Footwear Science, the teeter-totter effect was indirectly observed with the Nike Vaporfly 4% (VP4) running shoe. This mechanism was attributed to the presence of a curved carbon-fibre (stiff) plate, and potentially causes runners to propel forward during push-off. It was suggested that such mechanism should explain the 4% improvement of performance of the VP4 compared to regular shoes. However, there was, to the best of the authors’ knowledge, no attempt to associate this VP4-specific mechanism to the change in running economy and personal best time yet. Furthermore, a recent article published in the Journal of Sport and Health Science observed that the stiffening effect of the curved carbon-fibre plate plays a limited role in the energy savings, which therefore questions the presence of the teeter-totter effect in the VP4 shoe. In our view, the better running economy and personal best time obtained with the VP4 shoe cannot be currently explained from a biomechanical standpoint. With this letter, we would like to (1) summarise the specificities of the VP4 shoe, (2) report the observed improvements in running economy and personal best time, and (3) point out the absence of any biomechanical explanation to the better performance yet.