On Friday, World Athletics released new rules governing footwear that will put limitations on the technology allowed in competition.

World Athletics modifies rules governing competition shoes for elite athletes.

Details here: https://t.co/IA021EQfzR pic.twitter.com/9k0zgnf8Un

— World Athletics (@WorldAthletics) January 31, 2020

Among the new rules, recommended by a review group and adopted by the World Athletics Council, is a ban on prototypes in competition. Starting on April 30, 2020, shoes worn by competitors must have been available for four months prior to the race.

The days of a mystery shoe showing up on the feet of a top marathoner are soon to be over.

The other notable restrictions are a 40mm cap on sole thickness and a limit to one plate built into the shoe. These rules clearly signal the outlaw of the Nike Alphafly (at least as currently constructed), the prototype worn by Eliud Kipchoge in his 1:59:40 exhibition last October in Vienna. The shoe was never released to the public, but versions of it have been seen in recent weeks on the feet of select Nike pros. The shoe is rumored to contain three carbon fiber plates.

The track and field governing body has been under immense pressure in recent months to regulate shoe technology as Nike’s Vaporfly line of road racing shoes have been associated with precipitous drops in time among the world’s best distance runners. The carbon fiber plate technology in the shoe has been at the center of the controversy, with studies suggesting that the footwear can provide large improvements in running economy. 

However, this ruling appears to have spared the Nike Vaporfly Next%, the shoe that has been worn by droves of Nike athletes in the last year and has been credited, in part, with producing some record-breaking marks. Among them is Brigid Kosgei’s 2:14:04 marathon world record in Chicago last October and Geoffrey Kamworor’s 58:01 half marathon world record in September.

The Next% has a stack height of 36mm, well within World Athletics' new limit. The Alphafly's stack height has been rumored to be 50mm.

Friday’s release also established new rules governing spikes, putting a 30mm cap on sole thickness and allowing for two plates, “but only for the purpose of attaching the spikes to the sole,” the release read.