Is the highly engineered Nike Vaporfly just a shoe?

World Athletics, the governing body for track and field, is set to announce whether it’ll ban certain types of shoes. In particular, Nike’s Vaporflys have been prominently on the feet of athletes responsible for tumbling race records recently. Nike says that the $250 sneakers shave up to 4% off a runner’s time. But is that technology some sort of doping? 

I spoke with Iain Hunter, professor of exercise science at Brigham Young University, as he was with athletes training at BYU’s indoor track. He said the shoes work by combining foam in the sole with a carbon fiber plate. The following is an edited transcript of our conversation.

Iain Hunter: I think the plate mostly allows for some structure of the shoes. If that plate wasn’t there, and you have a 44 millimeter height off the ground that’s just foam, and you try running around a corner, that’s going to collapse on you. The plate mainly gives structure to the shoe, but it [also] gives a small benefit in terms of energy costs. Combine that with higher foam, because you can hold everything together with the plate, and you’ve got a really good pushing into the ground, big displacement of the foot while it interacts with the ground and then pushes off really effectively.

Jack Stewart: So it quite literally puts a spring in your step?

Hunter: Yeah. It’s not a coiled spring like we’re used to, but any foam is really a spring. This one’s just really effective at it. But where’s the line? That’s what the question is now. I think these are either at the line where I’d feel comfortable or a little bit beyond.

Stewart: So you’re saying that there could still be some innovation allowed in shoes? We’re not going to say everybody must wear the same type of shoe, but there must be a limit to it.

Hunter: Yeah, I think it’s wonderful to have the innovation on what Nike has done [to] propel other companies to catch up, and they will catch up. We could have the standard for marathon and a road racing as a shoe like the Vaporfly, but then Nike or someone will go a little further with it, and we’ll end up with 16 millimeter foam and enough carbon fiber to hold the structure of it so you’re not collapsing. It will just continue on. At some point, the rules need to standardize what a shoe is.

Stewart: The price of these shoes to us amateurs out there seems incredibly high. Is it what you would expect for a top-of-the-line running shoe?

Hunter: When they say $250 for a pair of shoes that Nike has mentioned probably will last about 90 miles before it’s losing some of its effectiveness. That is getting to the point of not outrageous, but people are going to be restricted by the cost of that, and they’ll be looking for cheaper options. If New Balance, Saucony and others start competing with the same quality and performance of shoe and are charging $150, Nike is going to have to start dropping their costs down. I think it’s naturally how marketing works, and it’ll all come to an equilibrium over time.

Stewart: I remember reading about the advantages that some forms of artificial legs could give runners potentially over runners with natural-born legs. Are we just reaching a point where sport is hard engineering?

Hunter: It is, and I think it should be, but there has to be some restrictions to how far you go. We don’t want people to be tempted to amputate their lower legs so they can go from a 2:15 marathoner to a 2:05 marathoner. Our legs aren’t built just for running, they’re built for climbing and swimming and jumping and all kinds of activities. If you tune the leg to be tuned just for running, they’ll be great at running but not good at other things. That’s where you could go if you didn’t have rules established.

Stewart: Given that these shoes do have a limited life, do athletes train in them and actually run in them in races, or do you hold them off for that performance boost when you really need it?

Hunter: If they’re sponsored by Nike, they’ll do all of their race pace work in those shoes. But if they’re buying their own shoes, what I typically see is they buy the pair, do maybe two workouts in them before the race — they probably have about 15 to 20 miles on them — and then they do the race. Then, they’ll maybe workout in those ones, but buy a new pair before the next race they do. That’s if it’s someone that cares about saving a couple minutes on a marathon time. I think it’s somewhere around one or two minutes, the benefit that most would get from this shoe.

Related links: More insight from Jack Stewart

Nike’s shoes first came to prominence in 2016 and were worn by the first three finishers in the Rio Olympics men’s marathon. An estimated 95% of the first 100 finishers in last year’s Valencia Marathon were wearing Vaporfly shoes. That’s just two of the statistics that Reuters has pulled together to show the dominance of this tech in different versions. There are also some graphs for my fellow data nerds. 

I also got lost in a new Wall Street Journal video on the shoes and the controversy around them, which some are calling a seismic shift.

Nick Thompson, editor in chief of Wired Magazine, is also a keen marathoner who set out to put these sneakers to the test himself by running the New York Marathon with them, all while crunching the data.

“They felt strange and wobbly at first,” he said. “My initial steps reminded me of putting on ice skates and then walking on a rubber mat to the rink. But once I started running, the strangeness disappeared, and I forgot I was wearing them.”