Controversial running shoes developed by Nike to enable the first ever sub two-hour marathon could be declared illegal in the coming months, with World Athletics set to introduce a rule that limits the thickness of a shoe's midsole.
In October Eliud Kipchoge ran a 1hr 59mins 40secs marathon in Vienna - a time ineligible for record purposes due to the use of rotating pacemakers - but the prototype shoes he wore sparked much controversy.
The Kenyan accomplished his feat wearing the Nike alphaFLY, the latest evolution in its Vaporfly series that was first seen at the top level in 2016. Nike did not respond to questions about the prototype worn by Kipchoge in Vienna, but patents filed by the company show that the alphaFLY contains three plates in its midsole sandwiched between layers of foam and forefoot cushioning pods.
The shoe is expected to go on general sale late in the spring marathon season, with an industry insider telling the Irish Independent it provides close to double the boost in running economy as previous editions.
The current rule states running shoes must not be constructed "to give athletes any unfair assistance or advantage" and must be "reasonably available to all", but due to Nike's heavily-patented design many believe that is not the case with the Vaporfly.
World Athletics' technical committee has studied the shoe since its general release in 2017 and a working group it commissioned containing two former athletes alongside experts in science, ethics, footwear, biomechanics and law is understood to have drafted a rule that will limit the allowable thickness of a shoe's midsole. The rule is expected to come into effect in 2020.