They are thundering down Bayshore Drive, bouncing along Brickell, climbing the Rickenbacker Causeway bridge, huffing through Hollywood, puffing through Kendall.

They are running — hundreds upon hundreds of South Floridians logging hundreds upon hundreds of miles in large, chatty herds.

Whether it’s dawn on a Saturday in Coconut Grove or Happy Hour on a Thursday on Lincoln Road, runners are gathering to train and socialize in sweaty support groups moving at a 6-10 mph pace.

The number of running groups has proliferated and their attendance has ballooned in lockstep with the growth of the ING Miami Marathon and Half Marathon, which will be at full capacity of 25,000 when the gun goes off downtown Sunday morning for the 26.2 and 13.1-mile scenic but grueling tours on blistered feet.

The annual race has become the incentive for locals aiming to set personal bests or get fit.

Miami is no Boston or Portland or New York, and it will always be too hot and too flat to be a running mecca, but the loneliness of the long distance runner has evaporated in the past five years.

“It’s taken a long time and we have a long way to go here, but we are becoming a real running city,” said Frankie Ruiz, co-founder of the marathon. “We’re looking a little like Central Park on the weekends. Our biggest asset is that we can be a 365-days-a-year playground.”

Ruiz, a man in motion, is the pied piper of the running group phenomenon. In addition to his job with U.S. Road Sports and Entertainment and as coach of the Belen team’s state championship dynasty in high school cross country, he leads three running groups.

He started with one group of six people four years ago. Now, on Thursdays, the Nike South Beach Run Club group of 150 takes off from Mr. R Sports. On Wednesdays, the Muscle Milk Kendall Run Club group of 200 gathers at SOLErunners. On Tuesdays, the Baptist Hospital Brickell group of 400 starts at Fortune International’s patio. Each has its own personality: Lots of young professionals and University of Miami medical students at Brickell; families in Kendall, and a “loud, festive and diverse” bunch on Lincoln Road. It’s all free and includes a core workout and the occasional scavenger hunt.

“I have observed a tremendous need for people to connect with people who share a passion for exercise as well as a desire to belong to a community that nourishes fitness via its public parks, sidewalks and safe places to run, walk and cycle,” Ruiz said. “Do you know that I cannot think of a single stretch of running path in Miami — outside an actual park — that goes for more than a mile without being interrupted by a parking entrance or intersection?”

Strength is in numbers, as the venerable Footworks staff has learned during years chaperoning groups from its South Miami store.

Then there’s Team FDC, as in Fernandez de Castro, as in Ralph, a Miami workboot salesman who started running in 2008 with friends and relatives and watched his group morph into a mass of 500. They meet Saturdays at 6 a.m. at Lot 67 near Miami City Hall. Some head toward Matheson Hammock on 20-mile runs. Others jog three miles around the Grove. Fernandez de Castro ran his first marathon in 2009, and 45 people from the group joined him. This year, 350 have registered for the half and full.