The best carbon plate running shoes now have to abide by a set of rules set by World Athletics, which were put in place in response to world records tumbling since the introduction of the original Nike Vaporfly 4% in 2017.
These rules include a limit of 40mm for the midsole stack height of the shoe and a maximum of one carbon plate in the midsole. These are the two main constraints that Puma has deliberately flouted with the Puma Fast-RB Nitro Elite LD, with the aim of seeing exactly what could be achieved in a shoe if you ignored the rules.
