The Nike Vaporfly 4% wasn’t shy about how much of a boost it claimed to give runners: the promise was right there in the name. When the shoe was released back in 2017, researchers at the University of Colorado published data showing that it improved athletes’ running economy (i.e., efficiency) by an average of 4 percent over the best marathon shoes at the time. Chaos—and a whole bunch of world records—ensued.
The key ingredients in the Vaporfly were a stiff, curved carbon-fiber plate embedded in a thick layer of soft-but-resilient midsole foam. Neither of these elements was magical on their own, but they somehow combined to make runners substantially more efficient, for reasons that scientists don’t fully understand and are still arguing about. Since then, virtually every major shoe brand has come up with multiple iterations of the so-called “supershoe,” tweaking these basic ingredients in minor and sometimes major ways.
But a key question has remained mostly unanswered: are the newest shoes significantly better than the original Vaporfly? A few researchers have run head-to-head tests of…
