On a Thursday evening in early September, the Upper West Side Run Club met on the steps of the American Museum of Natural History in Manhattan. It was 6:30 p.m., and temperatures were hovering in the low 90s. But despite the extreme heat, over 25 people, ranging in age from teens to late 60s, showed up to run a four-mile loop around Central Park.

They made frequent stops at the water fountains. They also played a game called “Liars” to keep their minds off the brutal conditions.

Usually the group heads somewhere after to wind down with a coffee or beer. It was the women’s semifinals of the U.S. Open, so about three-fourths of them went to Gin Mill, a gastro pub on Amsterdam Avenue, to cheer on the American players Coco Gauff and Madison Keys. Still in their running clothes, the crew, high on endorphins, drank beers and ate burgers, some staying until the matches ended after midnight.

“Every running club is different, but ours is very social,” said Maddy Nguyen, 25, a tech recruiter who started the club in February. “It’s very loose and very easy to hang with us.”

Running clubs — in which people meet to run and often do something social after — have exploded in New York City, offering runners of all boroughs, skill sets and goals the opportunity to be part of a community.

Those who join are finding not only health benefits — it’s easier to stick to a running regimen when you have people holding you accountable and helping the miles pass faster — but social ones. They are meeting best friends, neighbors, activity partners, even future spouses through the clubs.

“I think it was the merging of two things,” said Kristopher Imperati, 36, who works in a luxury hotel and lives in West Harlem. He heads Front Runners New York, a running club for L.G.B.T.Q. people and their allies, that currently has almost 1,200 members.

“I think a lot of people took up running during the pandemic because it was one of the few things you could get up and do,” he added. “But the pandemic also spurred this desire to be part of groups, to do social things.”

Indeed, according to a report by Nielsen Sports released in the spring of 2021, 13 percent of all surveyed runners began during the pandemic. Twenty-two percent of respondents who were already running before the pandemic said they started running more once it started.

As they experience growth spurts, New York’s running clubs are struggling with how to keep their communities intact and deal with breakoff factions. Some clubs have chosen to organize with an elected board, sponsors and membership dues, while others criticize those steps as alienating or acts of selling out.

Then there are the turf wars and rivalries that naturally arise with so many runners trying to operate in the same parks and spaces — sometimes annoyingly, as when other run clubs take up an entire path — and sometimes with civility.

“There is kind of this unspoken code among run clubs,” said Ryo Yamamoto, 47, a creative director and a co-founder of the Old Man Run Club, which meets on the Lower East Side. “It’s understood that the Brooklyn Track Club does track workouts on Tuesday, so we wouldn’t take that space because it’s their thing.”

The turf issues have even extended to the all-important social media handle. Ms. Nguyen started the Upper West Side Run Club in February because she was looking for people with whom to train for a marathon. “I made an Instagram page and posted a bunch on Upper West Side Facebook groups,” she said.

The exact same week, coincidentally, Oliver Barrett, 33, a classical musician who also lives on the Upper West Side, was trying to start a club for the exact same reasons. “I actually was going to call mine the Upper West Side Run Club, and I saw it was available on Instagram, but I thought about it for too long and when I went back to grab it a week later, it was taken,” he said, laughing. He named his club the Upper West Side Runners instead.

‘You See People at Their Lowest’

Felipe Toribio, 35, who works in accounting and lives in Brooklyn, met his wife, Ting Li, 31, through a club named NYC Bridgerunners that runs on Wednesday evenings out of the Lower East Side.

“We met there once, and then she messaged me through Instagram a few days later and asked if I wanted to go on a run together,” he said, explaining they were both training for the New York City Marathon. “Then we would see each other at least once a week at the club. I definitely tried to impress her.”

“It is very easy to get to know someone through running because it’s easy to get emotional,” he added.

For Sarah Sibert, 24, a film writer who moved from Indiana to Manhattan three years ago, in the early months of the pandemic, her run club, the Dashing Whippets Running Team, which has chapters in Manhattan and Brooklyn, is her main community.

“I literally had no one in New York City — my roommate was even someone I found online,” said Ms. Sibert, who ran track in college. “Now everything I’ve experienced in New York City has been with someone from the Whippets. We go to Broadway, we go to birthday parties, we go to bars.”

She said running was particularly conducive to bonding. “You see each other without makeup; you see each other exhausted,” she said. “Running is such a challenging sport mentally, so you see people at their lowest. I think it creates this sense of security even more than you have with other friends. It’s like family.”

Too Big to Bond?

In May, Will Truettner, 32, a creative producer who lives in the West Village, started the Village Run Club because he wanted a sober activity. “In New York City, it can feel like the only way to socialize with people is to go drinking or go to a restaurant,” he said.

He came up with the tagline “New York’s Slowest Run Club.” “I wanted it to feel like the average person can come and meet new people and have fun,” he said. The club does a three-mile run up the West Side Highway and keeps a slow pace.

The run club now has eight to 10 people show up each week, which, to Mr. Truettner, feels like an ideal size. “When we have seven or eight people running, everyone has a group chat,” he said. “But when it gets more than 15, everyone starts breaking off into groups, and it becomes harder to meet people,” he said.

Indeed, other run clubs are seeing the repercussions of getting too big.

Mr. Yamamoto, from the Old Man Run Club, used to pride himself on creating such a close-knit community. “We had one member going through health stuff, and the whole running community rallied behind her,” he said. “They did a GoFundMe.”

Now that the club attracts over a hundred people for each run, he has noticed smaller groups breaking away after the run to do their own activities. “I hate saying cliques, but there are cliques,” he said. “There are six people who always go off to do something after, and it kind of bothers me, because I love the idea of family.”

To Charge, or Not to Charge

“It’s an operation, for sure,” said Mr. Imperati, the Front Runners president. The club has an elected board of directors and several committees (among them, social and coaching), and members pay $30 in annual dues. The Dashing Whippets also charge $30 a year.

Mr. Yamamoto of the Old Man Run Club feels strongly that runners in his club shouldn’t have to pay to join. “It’s a free club, a come-as-you-are kind of thing,” he said. The club, however, is supported by Nike and Oakley, so members get glasses and merchandise throughout the year, though there is no requirement to wear them.

When Stephen McGowan, 37, who works in graduate admissions at Fordham University, started the BX Pints and Pavement running club in the Bronx in 2019, he swore off dues. “The membership fee is that you show up with an open mind,” he said.

“I think it’s really important in the Bronx to have no barrier to entry,” he added. “If you have a fee, even a small one, you are holding someone back from participating, and then there is no point.”

‘I Just Found My People’

While some clubs are trying to make a name for themselves by offering free merchandise, social benefits or “owning” a day of the week, others are content just to be one of many clubs in the city.

“I think that for me personally, a rising tide lifts all ships,” Mr. Imperati said. “The more people are out there running, whether they are with our club or another club or not at all, it creates more resources for others. There are more stores that cater to runners. Some of the clubs are putting on races.”

“I know people who are like ‘Upper West Side or die, I’m never going to another run club,’ but also people who attend more than one club because it’s a great way to meet new people,” Ms. Nguyen of the Upper West Side Run Club said.

But some people just find the right fit. “The first one you try is usually the one you stick with,” she said.

That’s what happened to Shahin Behnamian, 34, who works in cybersecurity, when he joined the Village Run Club. He had been looking at other clubs, he said, but “I started with this one, and it ended up being a good one. I just found my people.”