This September, when a local blogger mapped the 30.61-mile route Sylvester Stallone would have taken to complete Rocky 2's geographically improbable running montage, most readers took it as the ultimate punch line to a long-running cinephiles' joke.

Rebecca Schaefer, however, took it as a challenge.

The 25-year-old Center City resident quickly put up a website and organized what's known, in ultra-distance-running circles, as a "fatass" run. About 350 people have indicated on Facebook that they plan to join the Rocky 50K (that's not an extra zero), which will crisscross the city Saturday, using the route of that original post.

Such races - which often bear the catchphrase "No Fees, No Awards, No Aid, No Wimps" - are proliferating across the region. Think double-marathons, 100-mile challenges along busy city sidewalks, and grueling trail-running trials that incorporate creek dives and rock climbs - all without the hoopla.

Call it a running counterculture. Proponents eschew the high fees, competitive vibes, and commercial trappings of organized endurance races; they'd rather just get up off their you-know-whats and run.

"It hearkens back to the start of ultras," said Schaefer, noting the dramatic growth of long-distance running (and corporate race organizers) in recent years. "Rocky wasn't running for a medal; he was just running to train. So it kind of just fit."

Schaefer got a taste for no-fee runs last year when she joined the Great New York Hundred-Miler, a loop through four boroughs of New York City, beginning and ending in Times Square.

"If you've been running for 27 hours, it's an amazing place to finish," she said. "What cooler way to see New York City than running through it."

Other races of this kind range from casual training runs for a dozen runners to rugged competitions for a few hundred.

Still other events occur almost spontaneously.

Eva Basehart, 46, an Amherst, N.Y., ultra runner, this summer joined a handful of others in their own unsanctioned version of the Back on My Feet 20in24 Challenge Run (ideally, 20 laps of the 8.4-mile Schuylkill loop in 24 hours), after race organizers canceled the race due to extreme heat and expected lightning.

Basehart ultimately completed 75 miles, partly on the racecourse and partly on her hotel treadmill.

While Basehart had signed up for an official, supported event, she said she prefers the DIY ethos and camaraderie of no-fee runs. "Someone throws a challenge out, and somebody brings ice, somebody brings water, somebody brings oranges - and we got a race."

But whether it's running through Queens at 3 a.m. or scrambling up a trail as dusk falls, there can be risks as well.

Hunt Bartine, of Kennett, a member of a local running group called Trail Dawgs that organizes no-fee races, admitted that the group's most iconic event, the Mason-Dixon Longest-Day 100K, "can be a little dangerous."

Runners are challenged to complete a treacherous stretch of the Mason-Dixon trail during the 15 daylight hours on the summer solstice. Only about 10 people have actually met that challenge, out of about 200 attempts in the last eight years, said Bartine, 60. He has never finished the course by dusk, and is thinking of starting at 3:30 a.m. this year to give him extra time.

Interest has grown exponentially since Trail Dawgs began holding races in the late 1990s.

The first Mason-Dixon 100K in 2006 drew only two people, including Bartine. Now, registration is capped at 25. This past January, the group was caught off-guard when 350 people showed up for their annual Phunt 50K run, a no-fee event in Elkton, Md.

That has attracted the attention of authorities as well, to organizers' chagrin.

"It's getting harder and harder to organize these events, because parks services and other entities, like [the Pennsylvania Game Commission], have started to frown on the unorganized, not-for-fee unpermitted events," said Bartine, who has seen state authorities shut down races in recent years, sometimes at the last minute.

But that doesn't make the challenges any less tantalizing.

It's that mentality that drives Emir Dedic, 33, and his wife, Amy Dedic, 32, of Flourtown, who began running marathons a few years ago and quickly graduated to ultra distances. In April, they're heading to the Blue Ridge Marathon in Roanoke, Va., a sanctioned race over three mountains that they plan to make even tougher: They're going to do it twice.

The plan is to start about 2:30 a.m. to fit in the extra lap.

Why would a person want to do such a thing?

Louis D'Onofrio, another ultra runner, explained that participants want to test themselves, both physically and mentally - even if, as in the Dedics' case, it means their official finishing time will suffer.

"People who do these things tend to pride themselves in having a high discomfort threshold," D'Onofrio said.

The Center City lawyer often runs with a local group called the Animal Camp, which - among other events - celebrated Thanksgiving with an unsanctioned, two-hour trail run through the Wissahickon, featuring swims in the Wissahickon Creek and cliff dives into Devil's Pool.

"It's a big-challenge, big-reward kind of mentality," he said. "In a society and a culture where there's convenience and comfort and quick fixes, ultra running and trail running are challenging. It's kind of like exploration. It's like: Why do people climb mountains? It's not necessarily comfortable to be at 20,000 feet and climb Everest. You don't it for the view. You want a sense of accomplishment."

Basehart has been charged by bears on no-fee runs. Others have gotten dehydrated to the point of delirium, or cold to the point of hypothermia. And almost everyone has gotten lost - including Bartine, even on courses he marked himself.

"There's no shame in coming in last," Basehart said. "In fact, usually the ones that come in at the back have the best stories."