When Eliud Kipchoge made history by beating the two-hour mark for the marathon, the Kenyan was wearing a pair of controversial Nike running shoes that has sent rival companies scrambling to play catch-up in a business worth billions of dollars.
The likes of Adidas, Asics, Brooks, Hoka, New Balance and Saucony have recently released or are about to unveil their own carbon-fibre versions of running shoes.
Critics claim the new shoes are the equivalent of mechanical doping, while supporters hail them as a revolutionary technical advance in footwear after decades of stagnation.
Nike said its Vaporfly range, unveiled in 2016, was an "example of how product design can capture the fascination of an entire sporting community and, more broadly, inspire new benchmarks of athletic potential", boasting an improvement in times by up to four percent.
Elite athletes wearing versions of the Vaporfly, the carbon plates of which lend a propulsive sensation to every stride, have set a rash of personal bests and Nike runners have practically swept the board in long-distance events -- they took 31 of the 36 podium places at the six marathon majors last year.
Kipchoge was wearing an AlphaFly prototype boasting three carbon-fibre plates when he dipped under two hours in Vienna on October 12, while fellow Kenyan Brigid Kosgei was in ZoomX Vaporfly Next% shoes featuring a single plate when she set a startling new women's record of 2hr 14min 04sec in Chicago a day later.
Critics have been quick to question the advantage Nike-wearing athletes suddenly enjoyed. That led to World Athletics eventually stepping in to limit the thickness of the sole to 40 millimetres (Vaporfly are 36mm) and one embedded plate, while also insisting that running shoes had to be commercially available from mid-March to be allowed in elite competition -- that is, no more prototypes.
- 'Technology made other sports evolve' -
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"The key is that, at some point, all competitors must have access to similar or equal technology to ensure an equal playing field."
"The new foam allowed engineers and biomechanists to re-think the architecture of what was on someone's foot, and they demonstrated that substantial gains in performance were still on the table with equipment modifications despite having been largely stagnant for the better part of four decades."
- 'Absolutely unfair ' -
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"Others don't, as they see it as distorting the purity of the human performance. Everybody falls somewhere along that spectrum."
He said the controversial shoes were "by far" the leaders in performance and sales "because Nike is a successful marketing machine" and with a large percentage of the world's best runners under contract "their visibility and hype is much greater."
"The world woke up to a new reality. But it wasn't easy for other shoe companies to catch up to Nike -- it took time, and trial and error--and we still don't know how much they have closed the gap."