Nike's revolutionary athletics shoe, Vaporfly, has sparked the next great technology versus fairness debate in sport.
The shoes have been around since 2017 but Kenya's Eliud Kipchoge wore a prototype of a new version in October, becoming the first person to run a marathon in less than two hours (albeit pace-assisted). They were also worn by Kenya's Brigid Kosgei when she broke the women's marathon record last year.
Those successes have produced complaints the shoes give an unfair advantage — and calls to have them banned. The largely unspoken context, of course, is that athletes who are contractually committed to Nike's competitors can't use them.
Why are they special? They have a carbon fibre plate packed in foam. The thick soles and the plates act like springs to give runners more bounce, more carry. They apparently save more energy with each pace, pushing the runner forward with every step, making them more efficient over long distances; so efficient, some athletes are crying foul.
The first shoes were called Vaporfly 4% — as Nike maintained they saved the wearer four per cent in energy usage, a huge advantage in long distance races.
But hang on just a shoe-lacing second: we've all been here before. Technology has made huge, performance-enhancing and potentially unfair steps in other sports.
There's titanium and graphite golf clubs and hi-tech golf balls, huge (but light) cricket bats which have helped batsmen prosper over bowlers and the large-headed composite tennis rackets which took over from the smaller, wooden jobs (amid the usual chorus of "not fair").
So why not this time? World Athletics are deciding what to do about the shoes; various reports say they will ban them, others say they won't.
Surely such technology should be allowed because of what happens next. The competitors simply copy or advance the technology and everyone is back on a more or less level playing field.
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The comparison most made is with swimming's LZR body suits, designed by Speedo ahead of the 2008 Beijing Olympics and the 2009 world championships in Rome. Swimming's world body allowed the suits at both events and the impact is still felt.
The body suits saw a total of 108 world records fall before and during those events, leading to the world body banning them after Rome. However, the suits' impact was such that 11 of the swimming world records set then still stand.
The body suits gave an edge to wearers with polyurethane panels, helping swimmers become more streamlined. They also had neoprene flotation aids which gave them more buoyancy.
At Beijing, Speedo made their revolutionary LZR suits available to any Olympic swimmer — and they metaphorically knocked down old ladies in their haste to get one (94 per cent of all Beijing swimming golds went to swimmers wearing the LZR).
But what happened next was interesting. At the Rome world championships, Germany's Paul Biedermann beat the legendary Michael Phelps (everyone's choice as the world's best swimmer ever) in the men's 200m freestyle — wearing a new, even more technologically advanced, Arena body suit.
That caused further gnashing of teeth as many felt the better body suit had beaten the better swimmer; Fina banned the suits not long afterwards.
Biedermann's world record still stands — and probably will for many years.
It proves the point: technology marches on quickly; Speedo's suit was superseded by Arena's. So banning technology is probably not as desirable as ensuring everyone can get their hands on it — admittedly not always easy when sponsors, contracts and endorsements are involved.
Technology can't be uninvented, only uninvited. And let's face it — people like seeing world records being broken.
It's a thrill; a world record which is out of sight because it was set with banned technology is no fun for anyone. Sport can always use a few thrills.
Nike's shoe should be permitted — and competing shoe companies urged to come up with something equal or better before the Tokyo Olympics begin on July 24. Failing that, issue a Speedo-like credo making the shoe available to all.
The alternative: if the shoe is banned, Nike will appeal and the whole thing will drag through the courts, almost certainly undecided before the Olympics start, meaning the shoes would be prohibited there.
For spectators, which is the more interesting scenario?