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Machine Design

Putting A Spring In Your Step

Over the past few years, footwear manufacturers have been trying to design a shoe that reduces the impacts associated with running by using soft foams and viscous gels.

Putting a spring in your step

And although soft materials disperse energy and are softer on the feet, they make wearers feel like they are running in sand. As a result, runners have to exert even more energy to keep going. Engineers at Spira El Paso (, have come up with alternative that really works. They install a series of stainless-steel wavesprings from the Smalley Spring Steel Co., Lake Zurich, Ill. ( They also add a plastic midfoot support and a stable, two-density midsole to the shoe. In tests, the springs were shown to return over 87% of the potential energy that can used during running or walking to improve performance, more than any other shoe tested. The springs should never wear out and actually outlast the rest of the shoe, giving users a "new-shoe" feel for as long as they wear them. And proof that they do give runners and athletes an advantage is that the U.S. Track and Field has banned them from competition.

"We will be petitioning the USATF for a rule change," says Andrew Krafsur, president of Spira. "While we agree that proper interpretation of the rules prohibits use of shoes incorporating our wavespring technology for competition, we hope USATF reconsiders the rule in light of technological advances. So long as our shoes are widely distributed and available to all competitors, there should be no prohibition against their use."

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