The Rapid Rise of ‘Illegal’ Running Shoes
More runners are going for models with huge, cushy soles—even though some run afoul of racing rules
When a new breed of super shoes hit the distance-running scene nearly a decade ago, they turned the sport on its head.
No one was prepared for the Nike shoes with chunky soles injected with a carbon-fiber plate to suddenly make runners more efficient and so much faster. As other brands raced to catch up, world records were tumbling left and right.
The governing body of running, World Athletics, scrambled to rein in the Frankenshoes. One rule capped a shoe’s sole thickness, or “stack height,” at 40 millimeters—about 1.6 inches.
But recently, something strange has started to happen. Shoe companies started going over that limit, again and again, on purpose. Soles are now rising like cheese souffles, and runners are snapping up the super-sized shoes—even if they carry the risk of being disqualified from races.
“It’s just very simple biomechanics,” said Patrick Nava, global VP of running product at Adidas. “The more foam you have under your foot, the more comfortable it is, and the longer, usually, you can run.”
The brand boasts that its super-stacked Adizero Prime X2 Strung model is “not allowed in elite races.” It goes for $300 a pair and often sells out, Nava said. Adidas is preparing a new version of the shoe for this summer, also with a sole about 10 millimeters over the legal limit.
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Adidas also plans to make more shoes that ignore the rules. But there is a practical limit to how high they’ll climb before they worry about the shoes becoming unsafe.
“We tend to find that around 50 millimeters is probably a safe height to go to,” Nava said, “while minimizing the chance of falling over.”