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02/07/2020 Kevin A. Kirby, DPM
NJ Podiatrist Comments on Nike Vaporfly 4% Flyknit Shoes
The big story about the Nike Vaporfly 4% running shoes are not its upper material. Rather, it is the revolutionary combination of a compliant, resilient, and lightweight midsole foam along with a carbon-fiber plate embedded within that midsole foam that makes the Nike Vaporfly shoe so special. The name “Vaporfly 4%” came about since Nike’s own research by Hoogkamer et al, published in 2018, showed their shoe reduced the energetic cost of running in all 18 subjects tested, with the Vaporfly 4% shoe being about 4% more energy efficient compared to two other popular marathon racing shoes, the Adidas Adios BOOST 2, and the Nike Zoom Streak 6 (Hoogkamer W et al: A comparison of the energetic cost of running in marathon racing shoes. Sports Medicine, 48:1009-1019, 2018). The Nike Vaporfly 4%, and its newer model, the Nike Vaporfly Next%, both have a full-length carbon-fiber plates that are embedded within the midsole of the shoe. However, the most important feature that has made the Vaporfly more energetically efficient for runners is a new, more compliant, and resilient midsole foam, called polyether block amide, or "Pebax" foam. In their mechanical testing of shoe midsoles, Hoogkamer et al (2018) found that the Pebax foam of the Vaporfly shoes returned nearly double the amount of energy to the runner than the two other popular marathon racing shoes tested. In addition, the Nike Vaporfly 4% and Next% both have very thick midsoles which are ultra- lightweight which has allows these unique shoes to presumably store and more release more energy with each running step than other marathon racing shoes, being 40% thicker than other comparable marathon racing shoes. Without this thicker midsole, it is likely that the Nike Vaporfly models would not be able produce the same performance-enhancing effects that they have shown in elite marathon racers over the past 3 years it has been available to runners. This knowledge that shoe sole thickness helps determine the energy return potential of a running shoe, as long was shoe mass is kept to a minimum, is important when considering the recent ruling from World Athletics, published on January 31, 2020, which now bans running shoes from having a sole which is greater than 40 mm in thickness (https://www.worldathletics.org/news/press- releases/modified-rules-shoes). The Nike Vaporfly 4% and Next% are not just cool new running shoes. These shoes now currently hold the top five marathon times in the world. The Nike Vaporfly running shoe, by itself, has totally changed racing events in distance running to the point of where we are asking, was it the shoe, or the athlete, that allowed that record-breaking marathon performance?! Kevin A. Kirby, DPM, Sacramento, CA
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