Eliud Kipchoge captured the imagination and admiration of millions when he broke the mythical two-hour barrier for the marathon distance in Vienna last October.
For 26 miles and 385 yards, the Kenyan ran faster than most can sprint, crossing the line in 1 hour 59 minutes 40.2 seconds. Broadcast live on mainstream TV, it was a piece of sporting theater enjoyed by millions.
But did Kipchoge cheat? During the race he was wearing the Nike "Alphafly" shoe — a prototype of the "Alphafly NEXT%" that Nike said last week will be sold to the public and legally eligible for official races.
The shoes are thick-heeled with spring-like carbon fiber plates in the midsoles which help to push energy back into an athlete's stride. The new version is said to be even more beneficial to a runner than the 2016 Nike "Vaporfly" shoe which has seen official men's and women's marathon records tumble.
Kipchoge, speaking only a few weeks after his sub-two-hour marathon, defended the shoes.
"I respect technology. I respect innovation," he said. "The world is moving, and you can't stop. We are moving with the world, and the world is changing."
Closer to home, British athlete Laura Muir took five seconds off a 31-year-old British indoor mile record in February last year. The shoes appeared similar to Kipchoge's and the new record was briefly called into question.
Her coach denied their impact, claiming Muir could "run in high heels" and it wouldn't make a difference.
Nike Chief Executive John Donahoe has also rejected the idea that the technology gives athletes an unfair advantage.
"It's simply using the same materials that go into a shoe and putting them together in an innovative way that allows the athlete to do their very best in a safe way," Donahoe told CNBC last week.
But others aren't so sure. Robert Johnson, who edits the running site LetsRun.com, went so far as to say those who have benefited from the shoes in previous competitive races have been guilty of "mechanical doping."
And non-Nike athletes have petitioned World Athletics as to their fairness. Responding at the beginning of February, the sports body has set a maximum sole thickness of 40mm on trainers for the first time ever.
Nike's new shoe will, somewhat conveniently, have a sole thickness of 39.5 mm. That means it can be legally worn at the Tokyo 2020 Olympics by Nike-sponsored athletes.
While rival manufacturers will look to rush out their own versions, it seems possible that with only months to go, Nike's middle- and long-distance athletes will hit the start line in Tokyo with a serious advantage.
But this isn't cheating. This is the same forward crawl in sports technology that saw some sprinters first wear elasticated cycling shorts or put spikes on shoes for better grip.
Lighter shoes, gel inserts and improved grip have all been part of the advancement of the running shoe, and not all professional runners benefited from those developments at the same time.
And where is the line in the sand? Must we also strike modern records from the history books because they were achieved on springy tracks rather than the grass or sand of ancient Greece?
Nike has clearly pushed the technology on in one big bound. The firm will reap the benefit after Tokyo with casual runners — dreaming of improved speeds — heading to their stores.
It's a new race and the rivals will just have to catch up.
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