The 5 Essential Rules of Buying Running Shoes

The fit of your shoe determines how you run. Make sure you're not making these critical sizing mistakes.

June 13, 2017
train runner shoes

Adapted from Runner's World Your Best Stride

While the "comfort filter" covers the performance of the shoe, it also applies to fit. And fit, while often overlooked in our fascination with midsoles, might be even more important when it comes to how a shoe affects your stride.

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"Fit dramatically changes how you interact with the shoe," says Geoff Gray, PhD in physical therapy and founder of the Heeluxe footwear research lab. "And if you change how you interact with the shoe, that's going to change how you run. The shoe should accentuate your ability to interact with the ground, not limit it."

More: How to Start Running

The biggest error people make is in shoe size. Gray tests runners every day, including assessing how their feet move inside shoes. "We have something like 320 people in our database," he says. "Of those people, three-quarters of them are coming in a half size smaller than they should be."

The problem with shoes that are too small is that they limit the ability of your foot to flex and splay, both of which are critical to an effective stride. If your shoe is too short or too narrow, for example, it will affect your pushoff. "If there is some pinching on the toes, and you have good hip extension and you're getting good flex through the toes, your body recognizes that that is when the toes are getting squeezed the most," Gray says. "It is uncomfortable, so you'll start shortening up your stride or you'll start to push off with more pronation. Your body will make these micro-adjustments to get rid of that sensation. Your body is going to create limits somewhere so you don't get there."

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Gray sees several critical areas for fit. 

1. Length. "Your toes are supposed to be a thumbs-width away from the end of the shoe—that's important, because when you flex the shoe, as it bends, your toes are going to get closer to the edge."

2. Top of the foot, the instep. "Laces need to lock down on that area and give a secure fit. If you're not secure there, nothing else matters: It's going to be impossible to get a good-fitting running shoe."

3. Heel. "You want a secure fit to prevent the foot sliding up and down while pushing off, and you also don't want sliding side to side."

4. Ball of foot. Make sure it is wide enough. "The easiest way to determine if the shoe fits well: if you can actively spread your toes out and bring them back together as far as you would if you weren't inside of a shoe."

Natural running expert Mark Cucuzzella, MD, agrees with the emphasis on length and width: He reminds us that your foot under load will lengthen by up to half an inch and will splay by 15 percent—if allowed by the shoe. Get up on your ball in the shoe, put weight on it, and make it flex. Make sure the shoe is not restricting this movement.

5. End toe maiming. This last item of fit is perhaps the most important, and the hardest to find. The idea that shoes need to be wide enough in the forefoot to allow the foot to splay somehow got thrown out with the rest of the minimalist/barefoot movement. But podiatrists, physical therapists, and those who research feet say that crimping the forefoot doesn't allow the foot to operate properly.

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What is more, if the toebox is narrower than the ball of the foot, you are deforming your feet. "More than half of the people in the United States have foot deformity as a result of wearing shoes," says Shorten. "People end up with the shape of the toes looking like the shape of a running shoe." And it isn't supposed to look that way.

"Your foot is widest at the toes—but most shoes aren't built that way," says Cucuzzella. As a result of this shape, podiatrist Ray McClanahan says, "If you're an active adult American, you are slowly maiming your feet—and by extension, the rest of your body." He points out that bunions don't exist where people don't wear constrictive shoes. A bunion, in fact, is not a bone issue but "a progressive dislocation of the big toe joint."

The implications of this dislocation are significant. When your toe is pushing inward, you can't form your arch properly, and you lose foot strength and balance as a result. This then leads to problems up the chain, in the knee and hip. "If you can't stabilize your foot, you can't prepare for propulsion," McClanahan says. "Your brain senses that, and it is not going to let other prime movers do their jobs, because it realizes the foundation is not stable enough to do that."

More: How I Ran 75 Miles With Only Water

McClanahan has devised a plastic insert, Correct Toes, that helps push your toes back to a natural splay, and he agrees that all the foot exercises are helpful. But he feels the most important step to correct your feet is to get shoes that don't perpetuate the problem. "If you're going to wear a shoe for 8 hours with your toes pinched in, I don't know how much good you're going to do [with] 10 to 15 minutes a day doing rehab on your foot," he says. "It has everything to do with periodically kicking your shoes off, and, when you're not barefoot, try[ing] to be in a shoe that lets you spread your toes out a little bit."

Shoes across the board are starting to improve in this aspect, but nearly all are still narrower at the toe. It looks right to us, and companies cater to fashion. A few companies, notably Altra and Topo, and several minimalist shoe companies, treat this seriously and build shoes with room for your toes to align as they did when you were born. If you're serious about letting your feet move naturally, they are worth trying, even if people consider them "clown shoes." If nothing else, take width seriously and get shoes that let your toes moves.

Tags: runningGear