Luv2Run wrote:
You should check out the Science of Sport with Ross Tucker. They do a deep dive into the shoe.
There's no issue with Vaporfly and similar shoes. The stack height has been capped at a nominal 40mm. The Work-Energy theorem takes over now. The maximum amount of work that a runner can perform on his shoes is Force*Distance, and now, the distance is capped (40 mm, nominal). This means that for a given shoe size (i.e. size 8.5), and a given runner, there's a fairly rigid cap on the amount of energy the shoe can "store" because one of the two variables in the equation is fixed (distance, at 40 mm). The force exerted by the runner on the shoe should be roughly the same regardless of what shoe he's wearing, too. So, effectively, both variables are fixed, and the maximum energy stored by the shoe for a given runner is fixed. Give it a few years, and every flagship racing shoe will store as much energy as the next shoe. Saucony is already, according to informal shoe reviews (rather than lab data) coming pretty close to the Vaporfly.