In Vienna on October 12, 2019, Kenyan runner Eliud Kipchoge undertook his latest marathon attempt, which he completed at 20 seconds under two hours. However impressive, the record wasn't counted as official, as it was not in open competition and he used a team of pacemakers. In Berlin back on September 16, 2018, Kipchoge achieved an official marathon world record with a time of 2:01:39. To put this astonishing feat into context, that’s the equivalent of running 100 meters in 17.3 seconds and continuing at the same pace for another 26.2 miles.

Kipchoge, 34, is now regarded as the greatest long-distance runner of all time. He is a seasoned marathon winner, including an Olympic gold in Rio de Janeiro and three victories in the London marathon.

To top it off, he also seems like a genuinely wise, happy, and humble kind of guy. A New York Times profile tells of how he never ducks chores at his training camp high in the Kenyan hills: “He is a wealthy man, but he still scrubs the toilet.”

But his record-breaking marathon attempts (official or otherwise) have thrown up a few interesting questions. They don’t relate to performance-enhancing drugs — dozens of Kenyan runners have tested positive for banned substances, but Kipchoge's record is clean and few would suspect him of involvement — but they do concern what does or does not constitute an unfair advantage.

Kipchoge has something most other runners in the field did not: the benefit of Nike's latest and greatest technology.

Nike says the $250 Vaporfly 4% Runner, which was conceived as part of the brand's ambitious Breaking2 project (also featuring Kipchoge) to attempt a two-hour marathon, is named 4% because it offers an average 4 percent running economy compared with other top runners. Or in other words, how much energy runners use while running in them.

If you’re not a runner, that might seem small or inconsequential, but even small improvements in running economy can equate to shaving off minutes, not just seconds, over long distances. It’s an astonishing claim, and one that could easily be dismissed as yet more marketing hype to sell more shoes. But this time it actually appears to be true.

In Vienna, Kipchoge was dressed in a future edition of Nike’s NEXT% marathon shoe, which features a unique cushioning chamber in the forefoot, as well as ZoomX foam. The upper looks to be made of Flyprint 3D, which has been used on previous marathon shoes like the Zoom Vaporfly Elite. Nike has made no further details available about that particular shoe.

The New York Times analyzed data from around 500,000 marathon and half marathon running times — taken from public race reports and fitness app Strava — over the last four years. It 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.”

The same argument was made for the even newer Nike ZoomX Vaporfly NEXT%, which allowed Nigeria’s Brigid Kosgei to blow away the women’s world record for a marathon attempt made in two hours fourteen minutes and four seconds, shaving 81 seconds from the previous record.

If you’re a runner who takes races seriously, it's likely you're at least considering getting the these new Nike shoes. These innovations could arguably turn out to be the biggest step forward in athletics since rubberized artificial running tracks replaced crushed cinders — and for that Nike deserves tremendous credit.

But what does it mean for Kipchoge and Kosgei, who are breaking records using Nike's new shoes? Well, as sport scientist Ross Tucker pointed out after the Kipchoge's Berlin record, if what Nike says and what the NYT found are true, it essentially explains the record-shattering run.

Speaking about Kosgei, former marathon champion Gianni Demadonna told The Times, “They think the shoes are maybe allowing elite athletes to run two minutes quicker in the marathon. Understandably they are troubled by what is happening in their sport because the times being run are so fast. Even older runners are taking huge chunks off their best times.”

In Berlin, Kipchoge improved on the previous world record by 1.07 percent, which suggests Kipchoge and previous holder Kimetto were equal runners wearing unequal shoes. Lets Run's Jonathan Gault noted that, if you go by the New York Times study, you could even argue that Kimetto is the superior runner: "The Vaporflys were 1 percent faster than the next-fastest shoe in the study, but they were about 2.5 percent faster than the adidas Adizero Adios — the shoes Kimetto ran [in] during his world record run."

The effectiveness of Nike's new footwear is just another chapter in a saga that has plagued sporting officials for decades. At what point does new technology create an unfair or unsporting advantage? The International Association of Athletics Federations is certainly not turning a blind eye to the issue. The IAAF recently issued a statement to The Times noting, “Recent advances in technology mean that the concept of ‘assistance’ to athletes… has been the subject of much debate in the athletics world. The IAAF has established a working group to consider the issues.”

The US Golf Association banned balls that fly straighter than others, the NFL prohibited the use of a substance that helped players catch the ball, and swimming officials barred high-tech suits that reduced drag and increased buoyancy.

The difference between the Vaporfly or the ZoomX Vaporfly NEXT%, and other running shoes is that they have a carbon fiber plate in the midsole. That plate stores and releases energy with every step, meaning the runner expends less energy as the shoe propels them forward.

The International Association of Athletics Federations (IAAF) rules around footwear state that “shoes must not be constructed so as to give athletes any unfair assistance or advantage” and that they “must be reasonably available to all in the spirit of the universality of athletics.”

In a statement, Nike told Highsnobiety, "The Nike Zoom Vaporfly 4% meets all IAAF product requirements and does not require any special inspection or approval. The IAAF has also offered public support of the innovation. Furthermore, the shoe is available to every athlete via and stores."

It seems unlikely that the IAAF will ban carbon fiber plates, nor do most runners think they should. At least not yet. But the issue does throw up some interesting dynamics for the future of running shoes.

Will other brands try to catch up by using similar technology to level the playing field? How far can manufacturers push the technology? At what point does a world record become a creative technological feat rather than an outright physical one? Is the Vaporfly any different from, say, improvements in our understanding of nutrition?

As David Epstein asks in his excellent 2014 TED talk, are athletes really getting faster, better, stronger?

Nobody can really answer any of those questions right now, nor does anybody seem all that willing to try. To do so would unfortunately take some of the sheen off Kipchoge's incredible achievements.

In terms of the sport in a wider sense, it has been suggested that Kipchoge (and the Nike innovations on his feet) has effectively ended the era of other athletes chasing world records — simply because it seems unlikely that anyone but Kipchoge himself could seriously hope to improve on the official record now.

For more about Nike, check below.

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