Forty thousand runners. Eighty thousand tootsies. And nearly as many theories about the best shoes to put on them for the annual 10-mile stampede down Broad Street.
Neutral? Minimalist? Stability? Motion control? Cushioned heel?
Confused? Of course you are. Well, sports medicine specialists have good news. Stop worrying about fallen arches, overpronation, and putting your feet on a paleolithic regimen.
The latest thinking about how to choose the best running shoe is to let comfort be your guide.
Since the 1970s, running shoes have evolved from puny slabs of rubber sewn to canvas shells into engineering feats rivaling 3-D-printed surveillance drones.
Far beyond the latest Nike Flyknit Lunar 2 are plans for running shoes made of computer-generated molecules that will link to living organisms and conform to your foot's ever-changing needs.
In the somewhat-less-distant future are Google Bluetooth-enabled shoes that talk to you and tell you how your run is going.
For now, runners have a hard enough time picking from hundreds of mute, inorganic options.
"Historically, the push has always been to look at foot pronation," said Bryan Heiderscheit, a professor in the department of biomedical engineering at the University of Wisconsin-Madison. Runners were told to wear shoes that would correct for the foot's tendency to roll inward or outward, on the theory that this would correct biomechanical flaws and prevent injuries to the knees and lower back.
"But the best studies that have been done in the last 10 years," said Heiderscheit, "have not substantiated that claim."
In 2010, the American Journal of Sports Medicine published a study of 1,400 Marine Corps recruits. Half the group was given shoes based on a careful evaluation of the shape of their feet. The control group's shoes were chosen randomly.
"Assigning shoes based on the shape of the plantar foot surface," the authors concluded, "had little influence on injuries."
When Heiderscheit tries to explain this to members of the running-shoe industry, he gets "pushback."
Not surprising, he said, considering that the $20 billion athletic-shoe market sustains itself on innovation. Most companies release new models twice a year, offering features designed to improve performance and prevent injury.
The idea that almost any shoe is fine if it's comfortable is also apt to meet resistance from runners for whom theory has become dogma. Believers in barefoot running or minimalist shoes, for instance, are unlikely to be convinced.
Both are fine, said Heiderscheit, as long as recent converts do not make the switch too abruptly.
Speaking from personal experience, Heiderscheit said, it is easy to get injured if you decide to toss your cushiony sneakers and immediately start racking up miles in a pair of barely-theres.
It can take months to adapt, he said. He recommends exercises to strengthen muscles in the calf and foot and using the minimalist shoes for short, easy runs at first.
"You should feel so comfortable in a shoe that you could sleep in them," said Jon Woo, a sports medicine specialist at the University of Washington in Seattle.
Having competed in the Broad Street Run several times during his years at Jefferson Medical College, Woo knows the race attracts runners with an unusually wide range of experience, form, and training.
And although the pink tutus and "Will Run For Beer" T-shirts provide vital athletic support, without shoes that fit properly, those 10 miles can turn into a trail of tears.
Experts say that just as everyone's feet are unique, so are their running styles. "There is no absolute biomechanical ideal," said Heiderscheit.
One of the world's fastest marathoners, Pescah Jeptoo, has a knock-kneed gait that has carried her through 26.2 miles in a blazing two hours, 20 minutes, and 14 seconds.
Still, Heiderscheit said, there are "flaws" to avoid.
"You don't want to bounce too much. You don't want to overstride. And the one thing we absolutely don't want people to do is a hard heel strike - truly coming down on your heel with your foot pointed high in air."
Jeptoo, for the record, runs in Nike Zoom Streak 3s, a lightweight, breathable shoe with some support and cushioning. Online reviews of the shoe range from "I got huge blisters" to "Perfect!"
If this proves anything, experts said, it is that the one true authority on which shoes are best is the runner who wears them.
"That sounds about right," said Danielle Tolbert.
Nine days before her first Broad Street Run, Tolbert, a 37-year-old trade specialist from West Oak Lane, went to Philadelphia Runner on Sansom and 16th Streets to buy a new pair of running shoes.
Before pulling out shoes for Tolbert to try on, the saleswoman, Liz Foster, asked her to take a walk so she could evaluate her gait.
Foster, who is a serious runner herself, agrees that comfort is the overriding factor. But she rejects the notion that shoes do not prevent injuries.
"Anecdotally, I've seen a lot of injuries from bad shoes," she said. Runners who come to her complaining of knee and ankle pain get the proper shoes and return six months later feeling better.
"Try these," she said, loosening the laces on a pair of Sauconys for Tolbert. "This is going to feel much different."
For 10 weeks, Tolbert had been training for the race in Adidas Energy Boosts, which she'd bought online after getting recommendations from fellow members of her running group, Black Girls Run.
But then her ankles started hurting.
After trying on half a dozen brands and styles and testing them on the store's treadmill, Tolbert chose a pair of Mizuno Wave Paradoxes.
"I bought them," Tolbert said, "because they felt the most comfortable."