Advocates say running barefoot eases pain and opens up a new world of sensation.
Owen McCall threw away his running shoes and started running barefoot nine years ago.
He's been called crazy more times than he can count, and he remembers when a policeman came up, yelling at him to stop.
"I said, 'Yes officer, what's the problem, how can I help?'" McCall recalled, chuckling. "The officer got kind of contrite and said, 'Sorry I just had this vision flash in my mind that you were escaping from a mental institution.'"
Chelsea French, who took one of McCall's barefoot running clinics in May, said since throwing her shoes away, she's been sarcastically reminded that "she forgot her shoes" as she runs around her Chicago neighborhood.
She's also gotten another reaction: intense interest.
"I actually had a guy run up to me and pace himself with me for about a mile or two, asking me all sorts of questions," she said. "He's run I don't know how many marathons .. so I was kind of flattered."
Both runners said the main reason they run barefoot is to escape the aches, pains and injuries that they routinely experienced when running in shoes.
"I couldn't even fathom putting running shoes back on," said French. "The biggest difference is the bouncing up and down."
Instead of pounding the pavement, she said she's gliding across it when she's running.
"I feel like an ice skater," she said.
As running has become an increasingly popular sport, podiatrist Lisa Schoene said she's seen barefoot running wax and wane.
Right now, because of a new best-selling book called "Born to Run," there's been a resurgence of interest.
Given her profession, she doesn't love the idea, and she believes not everyone is suited for it.
"It's important not to put a blanket statement on it, like everyone should barefoot run. Our feet are genetically preset with a certain type of structure, so not everyone is going to be the perfect barefoot runner," she said.
In fact, Schoene said running barefoot requires really good strength in the core, hips and lower legs, and having good flexibility, which for many may require some focused training.
Whether you run with shoes on or off, Schoene said many people injure themselves.
"They just strap on a shoe and out they go. They have not really been trained to run properly, so many people have very, very poor form."
Like yoga, tennis, or any other sport, she says training is the key.
That's the first thing she suggests if people want to try going barefoot.
That's why McCall started his Chicago area barefoot running clinics.
He agrees that training is important and, like Schoene suggests, that people start slow.
"I don't coach people on how to run barefoot. Their feet feet coach them on how to run barefoot," he said. "In your first hundred yards, you will know more about proper running form than you have in your whole previous running career."
That's because when you wear a shoe, your heel is raised a little bit and that means your heel strikes first and the entire force of the strike gets transmitted upward through your body.
McCall remembers the pain from his running shoes days, but every time his foot has touched the ground in the last nine years, he said the weight has come off his heel and transferred to his foot.
The impact gets distributed in an entirely different way.
"It makes running more sensual. After you run a while, you realize, 'My feet were blind before,' because when you run barefoot you feel the temperatures and the textures, and it's like you have a new sense organ that you didn't have before," he explained.
As for stepping on things and running in the cold: he said on the coldest days he does wear flexible slip-ons designed for boaters, and he's had few problems with stepping on nasty objects.
Humans are designed to look where they're going, he finds, and their feet are designed to toughen up when people go barefoot.
"Anything you're doing that's natural and healthy shouldn't really involve pain," he concludes.
"There's no substitute for barefoot running. It's a conversation between your foot and the ground."