Do I Really Need New Running Shoes?

When Should You Buy New Running Shoes?

How long does a pair of running shoes last?

How often should I get a new pair?

These questions are two of the most often asked questions at running shoe stores. It usually comes up after the running shoe salesman has drug out three or four pairs of shoes and the customer likes more than one model. The customer then gathers final facts to come to a decision.

What are we talking about here? It's not whether the rubber on the outsole has peeled off, or stitching in the upper wears out. Rather, these questions are in regards to how long the cushioning and/or support lasts. The heart of shoe cushioning lies in the midsole—that foamy layer of, well, foam. It looks like marshmallow fluff. The most common bed of cushioning in running shoes is a rubberized form of EVA, the acronym standing for ethylene vinyl acetate, a thermoplastic polymer has applications ranging from surfboards to biomedical engineering. When you slip on a pair of untouched running shoes with a soft, bouncy midsole of compressed EVA, it can feel as if the floor beneath your feet has taken on the quality of a trampoline.

But as you and I know, that feeling—best described by Ray Bradbury in Dandelion Wine, with the character named Douglas magically bounding into the summer in a pair of "Cream-Sponge Para Litefoot Shoes"—doesn't last forever. At some point, you notice that they feel flat.

So the question, How Long Will They Last? usually refers to the life of the midsole. . Here are answers I've heard over the years of hanging out in running shoe stores and having worked in running shoe stores.

"Every 500 miles." (back in the 1990s, this is the one I used)

"Every six months."

"Every three months if you can afford it."

"Every 400 miles.

"Every 400 to 600 miles."

"Every 1000 miles."

"Depends on if you run on the roads or the trail."

"You can get more life out of them if you buy two pairs and rotate them in your usage."

No confusion there right? Not surprising since there are multiple variables involved. Not to mention the sticker shocks. Run 50 miles a week in $150 shoes and every two and a half months your gear-and-apparel budget is getting some serious drainage.

"Here are some fun facts," says Jay Dicharry, author of Runner's Anatomy: Unlocking Your Athletic Potential for Health, Speed, and Injury Prevention. Dicharry is a physical therapist and biomechanics expert, and is a key advisor to Ironman champion Linsey Corbin. Reports Dicharry, "One well designed research study shows that shoes lose about 40 percent of their cushioning by the time they've reached 200 miles. So the old adage to 'throw them out at 500 miles' isn't really an an all-or-nothing thing. Shoes break down with use, starting from the first step. And research shows that the body adapts slightly to adjust to these changes."

It's the last part that spurs Dicharry to let us know what can be done to take more control of the situation. Including the likes of Corbin, Dicharry essentially conducts research experiments with his clients and their biomechanics, studying the patterns of movement in fine detail to look not just for injury-inducing flaws that can be corrected, but for real-time, intricate adaptations that can help him better see opportunities for increased power flow.

"In general, people make small adjustments in their motion to minimize the mechanical work they are doing. It's kind of a self-preservation strategy to maintain efficiency."

Dicharry adds that sometimes these minute changes in range of motion are harmless. They allow a triathlete or runner to keep on trucking just fine in lifeless, broken down shoes.

"I had a previous runner that had excellent biomechanics," Dicharry says. "He wasn't really dependent on the shoe for anything, and routinely got 1200 to 1400 miles out of a single pair of shoes."

Right: Dicharry is talking about those runners like Dean Karnazes, who apparently have such perfectly-spun mechanics that they can run across the country and back with nothing more damaging than blisters.

As for the rest of us, one of the ways we know a shoe has lost it's cushioning is that nagging injuries start lighting up in the way of a pinball machine.

"There runners are more sensitive to the small changes in gait—either due to their structural needs as a runner or their biomechanics—and begin to feel symptoms brought on like clockwork every time they hit 'X'-number of miles."

What can we do? Dicharry encourages the latter-type of athlete (most of us, as suggested by injury data) be more like Karnazes and other seamless runners.

"One strategy to prolong the life of your shoes is to improve you," he says. "Make yourself less dependent on the shoes by relying more on your inherent foot stability." This is done, Dicharry says, by strengthening your feet. "Shoes do matter, and make a difference, but 100 percent co-dependent relationships are never a good thing."