Adidas has launched a new shoe in its Adizero line with two carbon plates and a super high 40mm stack height for maximum leverage, energy return, and speed. The Adizero Prime X 2 Strung doesn't comply with race regulations, which specify that a shoe can't have more than one rigid element running the full length of the sole or a stack height greater than 40mm, but it should be a lot of fun for runners who want to enjoy speed outside of competitive events.
Freed from the confines of race rules, Adidas's designers have really gone to town, packing as many speed-enhancing features into the shoe's midsole as possible. That includes three layers of Lightstrike Pro foam (more than any other Adidas shoe to date) to help reduce weight and provide extra springiness. It's all finished off with a Continental rubber outsole for grip.
The upper is reinforced in the midfoot and heel where durability is most important, with a little stretch in the forefoot for support and comfort. There's also a gusseted tongue to make your foot feel nicely locked in.
The Adizero Prime X 2 Strung will be available to buy from September 15 for $300 (about £240) via the Adidas app, direct from the company's website, from physical stores, and selected online retailers.
Why are dual plates illegal in races?
Whether they're made from nylon, carbon, or some other stiff material, rigid plates in running shoes act like a lever, meaning the ankle does less work, as BBC Science Focus explains.
The Nike Vaporfly shoes worn by Eliud Kipchoge during his 2019 sub two-hour marathon attempt contained three plates, plus Pebax foam, which is much lighter than conventional EVA and can compress and expand more quickly.
According to a peer-reviewed study (funded by Nike), the resulting footwear delivers a 4% increase in running efficiency, and an estimated 3.4% increase in speed. The impact is so great that similar shoes have been classed as a form of doping and banned from elite competitions in the interests of fairness.
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