Concerns over shoe technology grow after recent feats by Eliud Kipchoge and Brigid Kosgei

Growing concerns over the current technology in some running shoes could lead to tougher rules.

The spotlight has been thrust on footwear after Eliud Kipchoge's successful bid to break the two-hour men's marathon barrier in Vienna last weekend and Brigid Kosgei's obliteration of the women's world record 24 hours later in Chicago. Both Kenyans were wearing variants of Nike's Vaporfly, a shoe that laboratory tests claim can add up to a 4% improvement in running economy and oxygen usage.

Jake Riley, the leading American finisher in Chicago (but not sponsored by Nike), described the shoes like "running on trampolines."

The official marketing campaign of the shoe states that the construction consists of a patented foam and a carbon fiber plate that adds an extra spring in the step.

While not addressing the current controversy directly, a spokesman for the IAAF [the sport's governing body] said in a statement to ESPN.com that "it is clear some forms of technology would provide an athlete with assistance that runs contrary to the values of the sport.

"The challenge for the IAAF is to find 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."

Kipchoge's camp, however, suggested there is no real advantage.

"He feels there is less impact from the ground, which helps mainly with the recovery process after training/racing," Kipchoge's agent said in a statement to ESPN.com.

Nike could not be reached for comment.

While Kipchoge did not capture an official men's record, the purported marginal gains from the shoes are raising questions on what the limits should be following myriad concerns raised by athletes and rival manufacturers.

"Shoes need to be regulated with strict rules so that it's an even playing field for elites across all brands," U.S. half-marathon record-holder Ryan Hall said in a social media post. "I'm all about advances in technology that help us run faster. But I don't think athletes should be losing races because they are in a shoe that doesn't have a spring-like mechanism in them."

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CLARIFICATION: I feel the need to make a few clarifications on that last post as apparently people can't read without projecting their assumptions on it . • 1) I am no way trying to takeaway from @kipchogeeliud amazing performance this past weekend. I am continually blown away and impressed by his performances, which I thought I made clear by saying he is the GOAT "REGARDLESS of shoes". He did it. He broke 2 and I'll be the first to celebrate that. If you don't believe me listen to my interview on the @bbcnews. • 2) The only reason I posted was simply to state my opinion that shoes need to be regulated with strict rules so that it's an even playing field for elites across all brands. I'm all about advanced in technology that help us run faster. But I don't think athletes should be losing races because they are in a shoe that doesn't have a spring-like mechanism in them. This isn't about unreleased prototypes not being available, it's about mechanical advantage. Other sports have limits they place on the gear- cycling, triathalon, golf. So needs track and field.

A post shared by Ryan Hall (@ryanhall3) on

Although it seems certain Kosgei's time of 2 hours, 14 minutes and 4 seconds will be officially ratified, the IAAF will carefully examine this particular sneaker.

An advisory group composing of former athletes alongside experts in science, ethics, footwear, biomechanics and law was set up in April. It will establish whether the current wave of shoes violate the IAAF's Rule 143.2, which asserts that athletes cannot wear anything that provides "any unfair assistance or advantage" and also insists any product "must be reasonably available to all."

This could impact the lucrative global marathon circuit with some race chiefs privately fearing an unsporting domination amid this apparel arms race. They will await any judgment with interest despite the fervor generated by Kipchoge and Kosgei. "Their achievements were truly remarkable and have driven huge global engagement, which is great for the sport," Abbott World Marathon Majors executive director Tim Hadzima said. "The rules of the sport are governed by the IAAF, and we will continue to abide by those guidelines."

Said Hall: "This isn't about unreleased prototypes not being available; it's about mechanical advantage. Other sports have limits they place on the gear -- cycling, triathlon, golf. So [should] track and field." The advisory group is due to report back by the end of this year, raising the prospect of new regulations ahead of the Tokyo 2020 Olympics.