Eliud Kipchoge, the world's best marathon runner, wears Nike shoes — but do they help him run faster? You'll be truly astonished to learn that Nike says they do, however, until now, the full data and research upon which it makes this claim have remained pretty much private.

Kipchoge wears a souped-up version of the Vaporfly 4%. The "4%" name is taken from a Nike-funded study at the University of Colorado, Boulder’s “Locomotion Lab” that found test subjects wearing a Vaporfly prototype ran an average of 4 percent more efficiently than they did in other shoes. This weekend, the results of the study were finally published in the peer-reviewed research journal Sports Medicine.

The published report is quite staggering. Every runner tested — 18 out of 18, which, though it sounds small, is an above average number of participants for a study of this nature — had better running economy in the Vaporflys than when they ran in two other models (Nike's Zoom Streak 6 and adidas's Adios Boost 2). "We didn't want to compare the Vaporfly to Walmart specials," biomechanist Rodger Kram, director of the CU Boulder Locomotion Lab and the study's principal investigator told Wired. "We wanted to compare it to the best marathon racing shoes out there."

Running economy is a measure of the amount of work a runner has to do to maintain any given speed. If running economy improves, then the runner can go longer without building fatigue. The study did not show the participants ran faster when wearing the Vaporflys, but that they would run faster in a real-world setting, because they wouldn't have to expend as much energy to continue running at a given pace. The subjects included eight rearfoot strikers, and 10 midfoot/forefoot strikers, with the heel runners gaining a slightly greater advantage. The study also showed that running economy is improved no matter what speed you're running at, which is good news for amateurs.

The researchers attribute the shoe's performance not to its weight, as you might expect, but to its unique materials. The Vaporfly uses a light, compressible, and — most importantly, according to the research — springy foam. When the researchers simulated the running impact by pressing the shoes into a force-sensing plate, they found that the foam in the Vaporfly returned 87 percent of the energy it stored on impact. The Boost 2 returned 76 percent. The Streak 6 returned 66%.

Read more about the study over at Wired.

In other news, this health tracker sticks to your clothes and never needs charging.

What To Read Next