“You’ve seen the five-toed running shoes?” This was political commentator Keith Olbermann during an appearance on the Late Show with David Letterman in May. He had limped onto the stage with a cane and his left foot in an orthotic boot. When Letterman asked about the injury, Olbermann blamed it on the toe shoes. “They’re great for your knees. They’re great for your hips. They make you actually feel younger,” he said. “Unfortunately, if you try to run in them and you weigh more than 175 pounds, you will break something.”

Olbermann was talking about Vibram FiveFingers, a kind of glove for the foot made by the Italian rubber-sole specialist. For Vibram, this talk-show banter was a small public relations headache. It also was a signal of how popular its toe shoes had become since the company began peddling them six years ago. Back then nobody was interested, says Tony Post, chief executive officer of Vibram’s U.S. division. He first showed the design to his biggest sole customers to see if they wanted to partner on a product. They passed, so he brought it directly to retailers. They also balked. “It was just a little too strange,” says Post. This year the company is on pace to sell some $100 million worth of FiveFingers—a sum that will account for more than half of its North American revenue.

In between, barefoot running happened. A subculture of distance runners who consider the average shoe to be an affront to the human foot gained a broad following through a bestselling book and, along the way, created a market that is fast approaching half a billion dollars. In other words, people who believe you should run without shoes have kick-started a running-shoe boom. At the 750 running specialty stores tracked by the Leisure Trends Group, “minimalist shoes,” which did not exist as a category until 2008, now account for 9 percent of the market, with more than $24 million in sales so far this year. The mainstream retail chains, according to SportsOneSource analyst Matt Powell, are slated to sell $350 million worth of minimalist shoes for 2011. If you include “lightweight” shoes, a category created in 2009, sales could hit $1.8 billion. The trend toward less shoe, says Powell, is accounting for virtually all the growth in the $6 billion running market. The demand has shoe companies hustling to bring new products to market and wrestling with two big questions highlighted by Olbermann’s appearance on Letterman: Will people get hurt? And will barefoot shoes become everyday footwear?

At the moment, no one can agree on what makes a shoe barefoot or minimal in the first place. Powell reports he sent out 25 requests to industry sources for help to craft a definition and “got 27 different answers back.” Among barefoot enthusiasts, however, there is a simple litmus test: the heel strike. Their claim is that runners were never meant to land on their heels. We only began doing so about 40 years ago when cushioned shoes interfered with pain signals from the nerves in our feet. Blocking this information, the argument goes, disrupts natural, midfoot striding form and causes injuries.

The measure of barefoot belief, then, is how much padding shoemakers are willing to shave from the heel. A traditional running sole has 12 millimeters more cushioning in the heel than in the forefoot, or a 12-millimeter “drop” in the industry parlance. Vibram, Vivobarefoot, and Merrell—all newcomers to the running business—have courted the purists with flat profile, or zero drop, shoes. Established players New Balance and Saucony have taken a gradual approach and introduced 4-millimeter drop models before going to flats. Nike both anticipated and sidestepped the trend when it introduced the Free line in 2004. The shoes promised a “natural motion” with flexible, segmented soles and lightweight uppers, but left about a centimeter of extra cushion in the heel. Reebok basically did the same with the launch of its RealFlex line in April. Asics, meanwhile, has staked its place as a barefoot denier. In a video for Asics’ new 33 line, which can be found on Powell’s list of minimal shoes, Brice Newton, the company’s product manager for performance running, boasts that the shoes “provide a cushioned ride from heel-strike all the way through toe-off.” It may as well have been a declaration of war to the barefoot crowd. “If somebody’s running barefoot,” Newton says of the trend, “they’re running barefoot. We don’t really have a product for [that person].”

On this last point, Asics is in agreement with the hard-core disciples of barefoot running, whose bible is the 2009 book Born to Run by Christopher McDougall. Born to Run, which sold some half a million copies, is widely regarded as the catalyst for the barefoot boom. (Peter Sarsgaard has signed on to direct a movie adaptation.) The book tells the story of a group of ultra-distance runners who travel to a remote stretch of Mexican desert to race against members of the Tarahumara tribe. It also argues that “running shoes may be the most destructive force to ever hit the human foot” and that shoe marketing is a corruption of the sport. “Running isn’t about making people buy stuff,” McDougall quotes one of his main characters. “Running should be free, man.” McDougall says he’s been flooded with e-mails from people who say they read his book and went out and bought “the shoes,” which he answers with “When did I ever say buy shoes?”

The answer is a tale for the annals of product placement. In early 2006, says Vibram’s Post, a California man who goes by Barefoot Ted called him out of the blue. He had heard about the company’s yet-to-be-released toe shoe and was convinced it would be ideal for running. Marco Bramani—grandson of Vibram founder Vitale Bramani—and the industrial designer Robert Fliri, who designed the original FiveFingers, had no distinct purpose in mind. Bramani thought he might like to wear a pair on the deck of his boat.

As it happened, in the weeks before Ted called, Post had been experimenting with running in the shoes on the snowy roads outside his home near Boston. He was training for the Boston Marathon but had been hobbled by knee surgery. A friend suggested he try running barefoot. Post realized he had just the thing to protect his feet from the weather. “I ran a mile and then 2 miles,” he says, “and before long it was like, wow, maybe my knee pain is gone.” Post agreed to send Ted a pair and to pay his way to Boston to run in the marathon in April. In between, Ted went to Mexico to run in the 50-mile race that serves as the climax of Born to Run. Ted and his funny shoes became one of the book’s subplots.

Vibram officially launched the FiveFingers at the 2006 Boston Marathon. In the first year the company sold $430,000 worth, about 8,000 pairs. Sales roughly tripled in each of the next three years and then, following the publication of Born to Run in May 2009, leapt from $11.4 million to $54 million. At that point, Vibram couldn’t make them fast enough to keep up with demand. (Still, they aren’t for everyone. In June, the U.S. Army banned them, stating that they “detract from a professional military image.”) And Barefoot Ted (last name McDonald) has since launched his own company, Luna Sandals, and partnered on a new chain of Born to Run shoe stores that he reports will have 17 branches open by the end of next year.

Danny Abshire in Boulder, Colo., has watched the craze unfold with interest. A co-founder of Newton Running and longtime apostle of the midfoot stride, he helped pioneer a shoe that took the barefoot idea in a seemingly opposite direction. The sole of a Newton shoe looks like the X-ray image of a foot. Four small “lugs,” like rubber erasers, protrude from the bottom roughly in a line with the metatarsal bones that run the length of the foot. On contact with the ground, the lugs recess into matching chambers inside the sole and, as they pop back into place, help propel the runner forward. “If we go up to the second floor here and shove a piano out the window onto the concrete, ka-bam, a million pieces,” Abshire says, pointing out the window of his office. “That is like impacting concrete with a Vibram FiveFinger or barefoot.” In this piano analogy, the traditional running shoe is a foam mattress, while the Newton is a trampoline. Newton introduced its shoes in March 2007. In the first year, says Abshire, Newton sold about 30,000 pairs. This year they are in 280 U.S. stores and headed toward 150,000 pairs sold. In June, Fireman Capital Partners, the private equity firm run by Reebok founder Paul Fireman, took a minority stake in Newton. Abshire shrugs at the stripped-down shoes crowding the market. “Everybody else just minimized what they had,” he says. The Newton is “the foot plus.”

Whether they adopt “barefoot shoes” or Newton’s augmented soles, everyone in the business agrees that runners risk injury if they don’t change strides along with their shoes—and do so slowly. “If you try to do too much, too soon,” says Post, “it could ruin the experience.” For shoemakers it won’t matter where the fault lies. As long as runners blame their shoes, as Olbermann did on Letterman, they probably won’t be back for a second pair. “We’ve seen some of it already,” says Asics’ Brice Newton. “People getting injured and then moving back into the more traditional products.” In Olbermann’s case, Post says somebody from the company contacted his agent, who told the company that “Keith loves the shoes” and that his comments on air were just “his way of being funny.” In an e-mail, Olbermann disputes this: “Nobody’s called, written, visited, or expressed the slightest concern.” (“Maybe his agent didn’t bother to mention it to him,” responds Post.) While he calls the FiveFingers “the greatest shoes in the world to walk in,” he still blames his stress fracture on running in them. “I wore them for a year, walking and doing just short jogs—a minute or less—as part of workouts on treadmills,” Olbermann adds. “The day I suffered the stress fracture I had increased the duration of one of these sprints to three minutes. If that’s somehow my fault, what should one expect for a longer ‘misuse’? The Vibrams spontaneously combusting?”

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