Superfast Nike shoes are creating a problem

Last weekend’s extraordinary marathon performances — 1 hour 59 minutes 40 seconds by Eliud Kipchoge in Vienna and 2:14:04 by Brigid Kosgei in Chicago — have focused attention on an already simmering question: Does the International Association of Athletics Federations need a more stringent rule to define legal running shoes?

It appears that running, the original and most elemental of sports, now faces the same tradition vs. scientific innovation challenge that other sports have encountered. Think: tennis rackets, baseball bats and, perhaps most similar, competition swimwear — those polyurethane-based suits that were banned starting in 2010. The outcome of the current running-shoe debate could affect everything from stock prices of global footwear companies to who wins the Olympic marathon in Japan next summer.

Kipchoge, who became the first person to run the 26.2-mile distance in under two hours, and Kosgei, who set a women’s world record, raced in a revolutionary and bizarrely tall Nike shoe that has taken the marathon world by storm since 2016. In the last 13 months alone, male runners in the Nike shoes have recorded the five fastest marathon times ever. Other running-shoe companies are struggling to catch up, and may face patent hurdles.

The current I.A.A.F. rules state only that shoes may not confer an “unfair advantage” and must be “reasonably available” to all. The rule does not explain how these two values can be measured.

This week, the British Journal of Sports Medicine published a commentary that is likely to guide the debate. In it, Geoffrey Burns, a 2:24 marathoner and University of Michigan doctoral candidate in biomechanics, argued for “a single standard in competition running shoes: regulate the shoe midsole thickness.”

With the right material, a thicker sole produces more spring. Without clear restrictions, it is likely only a matter of time before someone comes up with a way to make a shoe with more powerful springs.

Burns called for an upper limit of 31 millimeters — about 1.2 inches — of midsole. Nike’s current Vaporfly 4% and Vaporfly Next% shoes have a 36-millimeter midsole, or about 1.4 inches. Why 31 millimeters? That’s a fairly common midsole height for previous models.

Until 2016, marathon racing shoes were constructed from thin slabs of rubber. In 1960, an Ethiopian runner named Abebe Bikila even managed to win the Olympic Marathon in his bare feet. Everyone understood that less was more; you ran more efficiently when you carried minimal weight on your feet.

In 1968, when shopping for the shoes that carried me to victory in that year’s Boston Marathon, I had only two criteria. They had to be light and thin, and they had to be cheap. I was still in college. I paid $9.95 for my lucky shoes — a pair of Onitsuka Tiger TG-4 Marathons.

Little changed in the footwear for elite marathoners in the next five decades, until Nike introduced its Vaporfly 4% shoes in 2016. These shoes contained a new midsole foam, Pebax, so lightweight that it is almost like running barefoot. Pebax also delivers 30 percent more energy return than the foams used in most running shoes since the 1970s. This allows Pebax to function almost like leg muscles, but without the fatigue that can debilitate the legs after 20 miles.

The Nike shoes also include a carbon fiber plate in the midsole. This plate might increase energy return, or it might improve foot function during the running stride. Either way, the plate is prominently mentioned in Nike’s patent application.

Nike-supported experts soon published papers in scientific journals showing that the Vaporfly shoes could improve marathon times up to 3 percent. That sounds small until you consider it is often the difference between a gold medal and a quickly forgotten fifth-place finish.

The results were so astounding, in fact, that some considered them as just another example of Nike sports marketing.

“I was skeptical at first, but then came the second and third and fourth report,” said Ross Tucker of the Science of Sport website. “I had to change my skepticism. Now I think the effect is real, and large.”

A 2018 New York Times data analysis based on public race results uploaded to Strava, the athlete-tracking and networking company, found that runners in Vaporflys ran 3 to 4 percent faster than similar runners wearing other shoes.

To be fair, Kipchoge, 34, is an otherworldly talent who has beaten the best in the world in last-generation shoes. There probably isn’t another marathoner who could break two hours in the shoes he wore last weekend.

(When I was with Runner’s World, I traveled to Kenya with a group from the magazine in 2005. Our dozen or so runners met with Kipchoge’s training group one day high in the Great Rift Valley. My wife wanted to get in a few miles, despite the altitude and a hilly course. I sheepishly asked the Kenyan runners if anyone was willing to run at a 12-minute-per-mile pace with us. Kipchoge stepped forward, an easy smile on his face, and did four miles with us.)

Still, the I.A.A.F. acknowledges that it has a problem, especially with the Tokyo Olympics coming up fast. In a statement, it said, “It is clear that some forms of technology would provide an athlete with assistance that runs contrary to the values of the sport.” The group has appointed a technical committee to study the shoe question, and make a report in the next two months.

Not every fast marathoner wears Nike shoes. Jared Ward finished sixth in the 2016 Olympic Marathon, and ran 2:09:25 in April in the Boston Marathon. When Ward lines up at the New York City Marathon in two weeks, he’ll be wearing Saucony shoes, as he has for years.

But not ones you can find at your local shoe store. Ward has been working with the biomechanist Spencer White, Saucony’s vice president for human performance, to design a shoe that is, well, a bit like the Vaporfly. Ward believes they have succeeded. “My new shoes feel so good that I know I’m ready to compete well in them,” he said.

Nike is well known in the patent world for its large and increasingly frequent applications. It also has plenty of lawyers, though no one can say what might happen in any patent infringement case until it is litigated.

White said he would be unhappy if the I.A.A.F. tightened its shoe regulation policies. “We could end up limiting creativity and losing the chance to improve running shoes for the everyday runner,” he noted. “I think the ‘must be widely available’ part of the rule is the best answer.”

Tucker’s view is more in line with Burns’s. “The solution is very simple,” Tucker said. “Limit the stack height” — which is the midsole height — “and ban the addition of springlike devices in the midsole.”

Burns would not even go that far. “I don’t want to ban anything,” he said. “We can do most of what needs doing with a simple midsole-height limitation. My fear is, if we don’t do this, in a few years we might end up with footwear that we don’t even recognize as shoes.”

Amby Burfoot won the 1968 Boston Marathon and was the executive editor of Runner’s World from 1985 to 2003. He has published six books on running, including, most recently, “Run Forever.”

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