Despite the cold and many other potential hazards, naked from the ankle down is the way Anna Toombs likes it, and she gets plenty of catcalls in the street as a result.
The 35-year-old co-founder of the personal training company Barefoot Running UK says she's lost count of the times people yell "where are your shoes?" as she and partner David Robinson negotiate London's parks and pavements to indulge their passion and train their clients.
"People give you a lot of weird looks," says Robinson.
They are also getting a lot of inquiries.
A surge of interest in "natural", or barefoot, training has seen runners around the world kick off their arch-supporting, motion-controlling, heel-cushioning shoes and try to feel the ground beneath their feet.
Top scientists - from sports physicians to podiatrists to evolutionary biologists - are jumping in too.
At a recent sports science conference in London, hundreds of participants, many of them shod but a few daringly barefooted, flocked to a two-hour long discussion about the merits or otherwise of running without shoes.
"It's a really polarised debate - there are what you might call the barefoot evangelicals on one side and the aggressive anti-barefoots on the other," says Ross Tucker, an expert in exercise physiology at South Africa's University of Cape Town and a middle- and long-distance running coach.
Born to run?
The current barefoot trend has its roots in the book "Born to Run", by Christopher McDougall. In it, he tells of time spent with Mexico's Tarahumara tribe who can run huge distances barefoot, often very fast, apparently without suffering the injuries that plague many keen runners in the developed world.
The debate centres on whether running in shoes with cushioned heels and supportive structures changes the way people move so dramatically that it's more likely to cause injuries.
Proponents of barefoot running say the natural way is more likely to prompt a runner to land on the padded and springy part of the foot, towards the front, rather than strike the ground with the heel as many shod runners do.
In a study published in the scientific journal Nature last year, Daniel Lieberman, an evolutionary biology professor at Harvard University, sought to find out how our ancestors, who ran and hunted for millions of years in bare feet or simple moccasins, coped with the impact of the foot hitting the ground.
Lieberman and colleagues from Britain and Kenya studied runners who had always run barefoot, those who had always worn shoes and runners who had abandoned shoes.
They found that barefoot endurance runners often land on the fore-foot before bringing down the heel, while shod runners mostly rear-foot strike, prompted by the raised and cushioned heels of modern running shoes.
In a series of analyses, they found that even on hard surfaces, barefoot runners who fore-foot strike generate smaller "collision forces" - less impact - than rear-foot strikers in shoes. Barefoot runners also had a springier step and used their calf and foot muscles more efficiently.
Lieberman, who spoke at the conference after an early-morning barefoot run along the banks of London's Thames, is keen to stress that the scientific evidence on whether barefoot running is better in terms of injuries is still very unclear.
"A lot of people are arguing on the basis of passion, anecdote, emotion or financial gain - but what's quite true is there are no good data saying whether it's better for you or worse for you," he said.
Having said that, he has already voted with his feet.
As has fellow biology professor Daniel Howell, who teaches human anatomy and physiology at Liberty University in the United States.
Howell, dubbed the "Barefoot Professor" by his students after he began living his life 95% shoe-free, admits he's an extremist.
He's spent almost all of the past six years in bare feet, he's run thousands of miles in all weathers and across many terrains without footwear, and he refers to shoes rather suspiciously as "devices".
"Barefoot is the natural condition. It's the most natural way to be," he told the conference. "Walking and running are extremely complicated from a biomechanical perspective ... and if you add a device to your foot, it alters it."
"When you put on a device, it changes the way you stand, the way you walk and the way you run. Those changes are unnatural, and generally negative."
(Reuters, December 2011)