Nike's controversial Vaporfly shoes will not be banned. Instead, all prototype technology not currently on the market will be temporarily suspended, The Guardian reports

• The man and woman who hold the marathon world records both compete in Nike Vaporfly shoes.
• Vaporflys give runners more energetic efficiency because the shoes' foam-and-carbon sole ensures less energy is lost with each step.
• Some researchers and runners think the thickness of the shoes' midsoles should be regulated to avoid unfair advantages.
• The Guardian reported Tuesday that the World Athletics organization (which oversees most international track and field events) will not be imposing a blanket ban on Nike Vaporfly shoes.
• Rather, World Athletics is expected to announce a temporary halt to all new shoe technology ahead of the Tokyo Olympics this summer, according to The Guardian.
• The official decision from World Athletics will be announced Friday.
• Visit Business Insider's homepage for more stories.

The man and woman who hold the world records for fastest marathon have something in common: They both compete in Nike Vaporfly shoes.

Both independent and Nike-sponsored studies have showed that the shoes increase athletes' energetic efficiency by 4% or more. Some runners and experts say the footwear confers an unfair advantage and should be regulated.

But the World Athletics organization, which governs most international track and field events, will not be imposing a blanket ban on the Vaporfly shoes, The Guardian reported. According to reporter Sean Ingle's exclusive scoop, World Athletics is expected to rule that all shoes currently on the market will still be legal.

The organization formed a working group of athletes, scientists, and legal experts to review the shoe and its technology last fall. World Athletics' official decision will be announced Friday.

Rather, according to The Guardian, World Athletics is expected to announce "a temporary suspension of any fresh shoe technology until after the Tokyo Olympics this summer." Going forward, World Athletics will likely insist that companies present any prototypes for approval prior to the shoes' use in competition, Ingle reported.

The Guardian also reported that the organization will launch a deep dive into examining how much more advantageous Nike's Vaporfly shoes are compared to other shoes, at the elite level. World Athletics did not immediately respond to Business Insider's request for comment.

Brigid Kosgei beat the previous world record by 81 seconds when she finished the 2019 Chicago marathon in 2 hours, 14 minutes, and 4 seconds wearing Vaporflys.

Eliud Kipchoge, who broke the men's world record during the 2018 Berlin marathon, donned a Vaporfly prototype named the AlphaFly in October when he ran the first sub-2-hour marathon ever. It's unclear what the expected announcement will mean for the AlphaFly shoe, as it is a prototype that's currently unavailable to the general public.

The controversy comes down to 'unfair assistance or advantage'

World Athletics' current rules say running shoes can't confer any "unfair assistance or advantage" and have to be "reasonably available" to everyone. But the organization doesn't define those standards more specifically.

Nicole Jefferies, head of communications for World Athletics, told Business Insider in an email on January 15, that the working group is also reviewing the wording of the rule.

The challenge, World Athletics said last year, is finding "the right balance in the technical rules between encouraging the development and use of new technologies in athletics and the preservation of the fundamental characteristics of the sport: accessibility, universality and fairness."

For 2 athletes of equal ability, the one wearing Vaporflys will beat the one without

Many runners sponsored by other shoe companies would like to see World Athletics issue rules about Nike Vaporflys. Sara Hall, an Asics-sponsored runner, told Outside Online last year that because of the shoes, "it's hard to really just celebrate performances at face value right now."

"I think it would help to have some limits, just like other sports have, like swimming, or triathlon, or cycling," she added. "They all have limits of the gear. So I think that would help create more of an even playing field."

A February 2019 study conducted independently of Nike found that the Vaporfly shoes improved an athlete's running economy by 4.2% compared to Adidas Adizero Adios 3 shoes.

"The runner runs the race, but the shoe enables him or her to run it faster for the same effort or ability," Geoff Burns, a kinesiology researcher and pro-runner, previously told Business Insider. "So for two athletes of equal ability on race day, the one with the shoes is going to beat the one without the shoes."