The Nike ZoomX Vaporfly NEXT%. ( Image)

Almost as swiftly as the records are falling, scrutiny is catching up to the elite marathoners and the Nike shoes they’re wearing.

Axios Sports pointed at the debate in a post on Friday, around the times clocked by Eliud Kipchoge, who ran the first ever sub-2-hour marathon, and Brigid Kosgei, who set a new women’s record of 2:14:04. What was on the runners’ feet — and others who have blazed through the 26.2-mile distance in recent years — is the focus.

The Nike ZoomX Vaporfly shoes, introduced in 2016, have a thicker midsole than traditional running shoes. According to an essay in The New York Times, this foam called Pebax is “so lightweight that it is almost like running barefoot” and functions “almost like leg muscles, but without the fatigue that can debilitate the legs after 20 miles,” Amby Burfoot wrote.

The shoe also contains a carbon fiber plate in the midsole which contributes to energy return.

The Washington Post also examined all that went into Kipchoge’s extraordinary accomplishment — the shoes, a laser-beaming pace car, and a “wind-breaking phalanx of pace-setting runners.”

Meanwhile, other athletes are weighing in, and reportedly complaining to the International Association of Athletics Federations and the Athletics Integrity Unit, in an effort to see whether it can be determined if the shoes provide an unfair advantage.