When runner Eliud Kipchoge made history last October, he had a secret weapon—super shoes! The world-class runner completed a marathon in less than two hours. No one had ever done that before. Mr. Kipchoge was wearing shoes that have been making the news.

The exact materials and design of Nike’s Alphafly super shoe are super secret. But what we do know is that the shoes are made with two air “pods” in the forefoot. Extra foam pads the heel. That cushions the foot against shock. It helps keep the foot from growing tired and gives a little bounce.

The shoe also contains a carbon-fiber plate. Energy from the runner’s leg would normally stop at the ground. The plate redirects that energy. It travels back upward. The runner is propelled forward with a little boost. 

What does it feel like to wear super shoes? One famous U.S. runner, Jake Riley, tells the BBC it’s like “running on trampolines.” 

During his historic marathon, Eliud Kipchoge wore an early Nike Alphafly model. America’s best male marathoner, Galen Rupp, won the U.S. marathon trials in March in a pair of Alphaflys.

But wait—marathons are supposed to be running competitions. Are they becoming shoe competitions instead? And is it really fair for runners to get such a big leg up from their shoes?

World Athletics is the governing body of track and distance running. It made new shoe rules. A shoe’s sole may be only so thick. It may contain only a certain number of plates. And any shoe headed to the Tokyo Olympics must be available to the public by April 30 of the year of the games. That’s so that anyone—not just big-money, company-sponsored athletes—can get a pair.