materials, especially midsole foam. Although t

[Labi1995]

Hoogkamer and Kram’s next study, published that fall with the innocuous title “A Comparison of the Energetic Cost of Running in Marathon Racing Shoes,” offered a more definitive assessment. The prototype shoe, compared with two top existing models—Nike’s Zoom Streak 6 and the Adidas Adizero Adios Boost 2 that Kimetto used in 201 4—reduced the metabolic cost of running by four percent. That savings, Hoogkamer and Kram calculated, “should translate to ~3.4 percent improvement in running velocity at marathon world record pace (20.59 km/h).” What’s more, because they normalized shoe weight across all three test samples, the benefit they found wasn’t from lighter weight.The study was instantly controversial. It was funded by Nike, for starters (Kram is also a paid consultant), and two Nike employees, Geng Luo and Emily Farina, were listed as coauthors.

Subsequent studies not associated with Nike have validated the results, although sample sizes have all been small and the resulting effect varied.Immediately, people questioned the role of the carbon fiber plate. “Any device inserted into the shoe, and which purports to add to energy return…should be banned,” wrote exercise physiologist Ross Tucker on his Science of Sport blog. Tucker maintains that the plate is essentially a spring, pointing out that this is how Nike refers to a carbon plate in a previous patent.Lost in the clamor over the benefit of the carbon plate was the role of the foam itself. In both their initial study and an early 2018 follow-up on the biomechanics involved, Hoogkamer and Kram pointed to one major contributor to the improvements in running economy: “That sounds like bland corporate jargon, but there may be more to it. And he’s a little wary of improvement that isn’t earned.

In plain English: The new foam was noticeably springier, which made runners faster.This foam, which Nike branded ZoomX, helped usher in a new era in shoe design and materials, especially midsole foam. Although the race for a breakthrough foam started in earnest in 2013 with Adidas’s first Boost-equipped shoe, Nike’s bold performance claims around the Vaporfly 4% and Next%, right down to the names, have changed the conversation. “When we started doing our outsoles, our focus was reinventing cushioning,” says Olivier Bernhard, cofounder of On Running. “Everyone you talk to nowadays, it’s about durability and resilience, rebound.”