Nike says that its Nike Zoom Vaporfly 4% are about 4 percent better than some of its best racing shoes, as measured by how much energy runners spend when running in them. That is an astonishing claim, an efficiency improvement worth almost six minutes to a three-hour marathoner, or about eight minutes to a four-hour marathoner.
And it may be an accurate one, according to a new analysis by The New York Times of race data from about 500,000 marathon and half marathon running times since 2014. Using public race reports and shoe records from Strava, a fitness app that calls itself the social network for athletes, The Times found that runners in Vaporflys ran 3 to 4 percent faster than similar runners wearing other shoes, and more than 1 percent faster than the next-fastest racing shoe.
We found that the difference was not explained by faster runners choosing to wear the shoes, by runners choosing to wear them in easier races or by runners switching to Vaporflys after running more training miles. Instead, the analysis suggests that, in a race between two marathoners of the same ability, a runner wearing Vaporflys would have a real advantage over a competitor not wearing them.
The Vaporflys — which retail at $250 a pair — were widely released to the public by Nike last summer. Unlike most running shoes, they have a carbon-fibre plate in the midsole, which stores and releases energy with each stride and is meant to act as a kind of slingshot, or catapult, to propel runners forward. Compared with typical training shoes, the Vaporflys are believed to wear out quickly: Some runners have said they lose their effectiveness after 100 miles or so.
The apparent effectiveness of the shoes highlights an issue that has vexed sports officials for decades: how to determine which technological advances constitute an unfair competitive advantage. Golf officials barred the use of certain balls that fly straighter, the N.F.L. barred the use of a sticky substance that helped players catch the ball, and swimming officials barred high-tech suits that were said to have enhanced buoyancy and speed.
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