The modern running shoe appeared three decades ago, when companies began adding foam to cushion the runner's foot. Now, manufacturers are busy ripping it out again, replacing it with more sophisticated materials. Suddenly, the recreational runner has a world of choice in running gear: solid composites, new forms of compressed gas, and air.
"You're going to see more and more companies trying to become less dependent on foam," says Steve Young, a marketing manager for Nike Inc.
The reason: Foam gets permanently compressed after a repeated pounding and ceases to offer much cushioning.
Nike for years has pushed its Air line of shoes as an alternative to foam-based footwear. (Nike Air isn't really air, it's compressed gas). Now, the Beaverton, Ore., manufacturer is pushing more advanced versions that use air modules at different pressurization and a new line of ultra-thin gas-filled soles called Air Zoom.
Puma AG claims that foam is dead. The German manufacturer is touting a foamless shoe, which uses a cushioning material called polyurethane elastomer instead.
The company that has made the biggest splash with a new cushioning technology is Reebok International in Stoughton, Mass. On April 1, it began selling its DMX running shoe, which has two layers of air cushioning. The air not only protects the foot, it controls its movement.
That control is crucial. For years, running-shoe designers have had to make a basic compromise. They had to put enough cushioning in their shoes to protect the heel, but not so much that a runner's foot would "wobble" and get out of sync with the working of the knee. In the late 1970s, Barry Bates, a professor of biomechanics at the University of Oregon, was one of the inventors that came up with a solution using foam.
Reebok's DMX innovation is to use air (real air this time, not compressed gas) that moves to various parts of the sole at specific times.
For example, when the outside of the runner's heel touches ground, it lands on a cushion of air. As the runner's weight bears down, that air is pushed to the inside of the heel, which keeps the foot from rolling inward too much.
Meanwhile, another air-filled layer is forcing air toward the forefoot. When the runner's weight is on the forefoot, the air travels back to the heel. Spencer White, director of research and engineering at Reebok, calls it the biggest innovation in running-shoe technology since manufacturers started cushioning their products three decades ago.
Dr. Bates at the University of Oregon is skeptical. All shoe technologies are partly marketing programs. Still, there's no question the company has gained a lot of attention with DMX.
"This is like no other shoe that has come out on the market," says J'eannette Davis, a customer relations representative at a San Diego mail-order running-shoe company who has tried out the new shoes. "It's very cushioned, very comfortable. I liked it."
Reebok hopes publicity about DMX will help it regain market share against industry-leader Nike. The company will come out with a DMX cross-training shoe in July and a basketball version next fall. Since the current running model costs $110, Reebok also hopes to come out with a lower-cost version later.
So far, Nike is sticking with its current Air technology by adapting it for ultra-lightweight shoes for runners who need little cushioning and dual-pressured pods that cushion and stabilize at the same time.
But more innovations will come in the next year or two. "There are some things that we are very, very excited about that have taken us further than today's technologies go," Mr. Young says.
So foam is on its way out - unless Reebok succeeds in a version so durable, it wouldn't even need a rubber sole.
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