I would say some of it is mental. People simply believing they can run faster because they have said shoe on. It is advertised that way. I really don't think a shoe can make people more efficient in running. After all they have to put down the energy for it to be returned at all. Its kinda the same thing that happened when bannister broke the barrier. Kipchoge ran a 2:01 in the shoes and everyone else thinks they can run faster in them in.