One year ago, longtime recreational runner Nancy Mize of Raleigh decided to ditch her trainers and try running in bare feet.
Vexed by foot and knee problems, she stopped in the middle of a track workout, took off her shoes, and ran several laps in just her socks.
Mize's recurring running injuries soon cleared up.
"I haven't worn regular shoes since," she said.
She's among a small but devoted band of barefoot advocates that is trading the cushioning and stability of traditional running shoes for bare feet or minimalist footwear.
Converts argue that running barefoot - or close to it - improves form and reduces injury. Could they be right?
Researchers at UNC-Chapel Hill are trying to find out.
"Everywhere I go people ask me: 'What's the deal about barefoot running?' " said UNC-Chapel Hill physical therapist Michael Gross, P.T., Ph.D.
Like many physical therapists, Gross has spent years counseling patients on orthotics and corrective shoes.
With a "back to basics" movement now afoot, Gross and his Ph.D. student Donald Goss are studying the risks and benefits of this fast-growing fitness trend.
The McDougall effect
Today's athletic shoes offer loads of features to cushion and correct the feet - from stiff arch supports and super-cushioned soles, to roll bars, thrust enhancers, memory foam and microchips.
For all their high-tech features, the incidence of injury has stayed the same.
"Roughly half of the 36 million runners in the United States get injured every year. It's been that way since the 1970s when running shoes were introduced," said Goss, who treated soldiers in the Army for 14 years before accepting a scholarship to pursue a Ph.D.
If running shoes do little to prevent injury, some say we may be better off in no shoes at all.
One of them is Christopher McDougall, author of the best-selling "Born to Run."
McDougall's book tells the tale of the Tarahumara people in northern Mexico, who routinely run 100-mile races in little more than thin-soled sandals. According to him, encasing the foot in cushioned or corrective shoes allows our muscles to atrophy and prevents sensory information from reaching the feet.
Soon after McDougall's book came out, the American Podiatric Medical Association released a statement cautioning runners against jumping on the barefoot bandwagon, noting the lack of scientific studies and warning that stray rocks or rusty nails could mean disaster for naked feet.
A new line of "barefoot" shoes with thin flexible soles has emerged to mimic the feel of going barefoot while protecting against cuts and scrapes, but some are still skeptical.
"Personally I think the barefoot shoes are more of a marketing gimmick," said UNC Charlotte cross country coach Ed Schlichter.
Some researchers have begun to wonder if it's not what's on your feet that's important, but how you run.
For most of human history, humans ran in thin-soled sandals or moccasins, or in no shoes at all, notes Harvard anthropologist Daniel Lieberman.
To find out how people managed to run comfortably before running shoes came along, Lieberman and colleagues traveled to the Western Rift Provence in Kenya - home to many world record holders in distance running - to compare people who grew up wearing shoes with those who had never worn shoes at all.
Those who grew up wearing shoes tended to hit the ground heel-first.
In contrast, those who had never worn shoes landed lightly on the middle or ball of the foot rather than heavily on their heels.
"Barefoot running forces you to run more lightly and gently. You can't crash into the ground the way you can with a shoe," Lieberman told attendees at the 2011 meeting of the American College of Sports Medicine this June.
Experts agree that running barefoot - or close to it - forces you to change your form. But what does that mean for injury?
Last year, Gross and Goss launched an online survey to look at injury trends associated with different shoe types and foot-strike patterns. They've gotten more than 2,400 respondents so far - people between the ages 18 and 50 who run at least six miles per week.
Although not yet published, preliminary results suggest that different shoes and running styles may make people prone to different injuries.
"We're seeing differences in the rate and location of injuries among people with different foot-strike patterns and shoe preferences," Goss said. "Are we just trading one set of injuries for another?"
This summer, Goss and Gross started bringing runners with different running styles into the lab to measure the impacts on their legs and feet.
They're studying traditional and barefoot runners, but they're also looking at people specialized in other running techniques, such as the "pose" method and ChiRunning - the latter developed by Asheville running coach Danny Dryer.
With eight high-speed cameras peering on, a study participant in minimalist shoes runs on a treadmill in the Human Movement Lab at UNC-Chapel Hill.
A computer uses light reflected by silvery gray markers on the runner's hips, legs, ankles and feet to build a 3-D model of his legs in motion.
"Notice that he's landing with his foot nearly horizontal, and taking short, quick strides," Goss says. "A typical heel-first runner does 140-150 strides per minute, but in midfoot and forefoot runners that goes up to 180."
Goss points to a graph showing the pounding forces on the runner's legs, from the instant his foot touches the ground to the moment it pushes off.
"We experience forces equivalent to two to three times our body weight each time we land," Goss says.
Landing on the ball or front of the foot avoids the hard heel strike and softens the initial blow.
"Someone who has a history of knee injuries may be able to save their knees if they run with more of a forefoot-strike pattern," Gross says.
But there's a tradeoff, he adds, holding up a plastic model of a foot and pointing to the long bones leading up to the toes.
"Shorter strides also means more steps per mile, which means more cumulative stress to the foot. People who already have a history of metatarsal stress fractures are asking for trouble."
More than a fad?
Barefoot advocates point to top-tier runners like 1960 Olympic marathon champion Abebe Bikila and to 5,000-meter world record holder Zola Budd, both known for barefoot racing.
But UNC cross country coaches still use barefoot running sparingly as part of their training programs.
"We do some barefoot strides in the grass once a week at the end of our workout to strengthen the feet, but we limit it to 400 to 800 meters," said UNC Asheville cross country coach Jesse Norman.
So is barefoot or minimalist running more than just a fad?
Before tossing aside traditional shoes, experts say to start small, gradually increasing your speed and distance.
In the end, what running shoes and styles are right for you will depend in part on your past injuries, they say.
"Your injuries, but also your genetics, whether you're bow-legged or knock-kneed, what activities you choose to do - all of those factors play a role too," Gross said.