CNN  — 

Running is supposed to be one of the purest sports, but a technological arms race in shoes is raising questions about the integrity of competition in athletics.

Times have been tumbling in long distance road races and critics are suggesting some cutting-edge trainers are artificially boosting performances.

The concern is such that World Athletics – the sport’s governing body – has convened a panel of experts to look at the legality in professional competition of a range of modern shoes.

Eliud Kipchoge wore a protype Vaporfly – the Alphafly – when he became the first person to run a sub two-hour marathon last year, although the time wasn’t ratified by World Athletics because it was not set in a proper race.

Kenya’s Brigid Kosgei also wore Nike’s Vaporfly Next% when she beat Paula Radcliffe’s 16-year-old women’s marathon world record last year.

The shoes, along with similar designs from other brands, feature thick soles and carbon plates which act like springs.

NEW YORK, NEW YORK - NOVEMBER 03: Geoffrey Kamworor and Joyciline Jepkosgei of Kenya pose with the Kenyan flag after winning the Mens' and Womens' Division of the 2019 TCS New York City Marathon on November 03, 2019 in New York City. (Photo by Sarah Stier/Getty Images)
Kenyan runners dominate 2019 New York City Marathon
01:10 - Source: CNN

‘Universality of athletics’

While the Nike shoes are perfectly legal, an initial study in the journal Sports Medicine in 2017 suggested Nike’s original Vaporfly 4% offered a boost in running economy – the measure of the amount of work a runner must do at a given speed – of about 4% compared with another Nike model and a top trainer from Adidas.

A New York Times study in 2018 and another independent review in February 2019 confirmed the findings. According to the New York Times, the top five fastest men’s marathon times in history have been set by runners in Vaporflys.

World Athletics’ rules say shoes “must not be constructed so as to give athletes any unfair assistance or advantage.”

Rule five adds: “Any type of shoe used must be reasonably available to all in the spirit of the universality of athletics.” The Vaporfly Next% are widely available at retail at a cost of more than $300.

The wording also says that shoes deemed as being non-compliant “with the rules or spirit of them” could be banned from competition.

In a recent statement, World Athletics said a working group, including officials, athletes, scientists and lawyers are reviewing shoe technology and the wording of the rules.

A decision is likely by the end of this month, but any change must be approved by the World Athletics Council, according to a spokesman. CNN has reached out to Nike for a comment but has yet to hear back.

Kenya's Eliud Kipchoge became the first person to run a marathon in under two hours.

‘We must go with technology’

Kenya’s Kipchoge set the official marathon world record of two hours one minute 39 seconds in Berlin in September 2018, and clocked 1:59.40 in the special INEOS 1:59 Challenge event in Austria. His support runners in Vienna were also wearing the Vaporfly shoes.

Kipchoge likened running a sub-two hour marathon to Neil Armstrong’s historic moon landing in 1969 and the Kenyan sees nothing wrong with the advancement in shoe design.

“They are fair,” he told the Telegraph. “I trained hard. Technology is growing and we can’t deny it – we must go with technology.”

Swimming is another sport that has had to contend with the consequences of technological improvements.

At the Beijing Olympics in 2008, 94% of all swimming races were won by athletes wearing Speedo’s LZR Racer swimsuits, according to Time Magazine.

After 17 world records fell at the European Short Course Championships later that year, the International Swimming Federation (FINA) changed its rules regarding the length and material of swimsuits.

Kenya's Brigid Kosgei won the Chiacgo Marathon in a new world record of 2:14.04 in October.

“We’re talking about performance integrity,” said respected sports scientist Professor Ross Tucker, talking to CNN ahead of Kipchoge’s sub-two-hour attempt in October.

“Is Kipchoge an outlier of immense athletic potential? Or is he a simply a very good runner who is benefiting from the immense improvements that his shoes provide? Perhaps both.

“But the point is we don’t know with absolute certainty. Running, especially marathon running, is supposed to be the purest thing humans put themselves through. It’s just about feet, legs, lungs, heart and brain. These shoes create the same problems that doping throws up.”