These shoes, which have fully entered the mainstream of the running world, are expensive. The Nike Alphafly 2 shoes currently retail at $285. The latest Vaporfly shoes are “just” $260.

Klein, however, is concerned about the long-term consequences of the true stars of super shoes—the midsole foam. Fly Now, Pay Later? “My big question has to do with tendons,” Klein says.

World Athletics, the sport’s governing body, insists that all such super-shoes should be available to all athletes in order to be legal, so there is no risk of results being determined by a lack ...