They hog the treadmills. They clog all the classes. They wander around with journals, writing down every rep.

And, in a few weeks, many of them will be back on the couch.

It is January, the month when the New Year’s resolution throng descends on the gym. For the $20 billion health club industry, it is an annual cash cow as gyms dangle big deals to lure the “I’ve got to lose weight and get in shape’’ crowd into long-term contracts.

But for gym regulars, it is the month of dread, when eyes are rolled and routines adjusted to avoid the long lines formed by the resolution rush.


“It’s kind of the same thing as how people who go to church throughout the year feel on Christmas and Easter when it’s so crowded that you have to get there an hour-and-a-half early to get a seat,’’ said Terry Stone, a 41-year-old management consultant from Charlestown who goes to both religiously. “It’s so annoying.’’

Ben Valentino, general manager of the Boston Sports Club’s Fenway location, looks forward to this time of year, both for the business - “This is our black month, the month that determines our year’’ - and the accidental comedy.

“They’re so easy to spot. They have their iPad in front of them looking at exercises. They have the iPhone apps that are supposed to be personal trainers. They sprint on the treadmill instead of running. They’re just 110 percent gung ho,’’ he said. “But they don’t know how to pace themselves, so they burn out, or injuries arise. Ninety percent of the time, they’re gone in two or three weeks.’’

For the regulars, surviving those weeks - most put the over/under somewhere around Valentine’s Day - is just a part of gym life, said Tim Fraser, a 28-year-old lawyer from Chelsea.


“It’s twice the amount of people, easily,’’ Fraser said as he was entering the Equinox gym next to the Back Bay MBTA station. “This is a big gym, but I haven’t been able to find a place to jump rope since the new year.’’

As Carrie Pennewell prepared to enter the Boston Sports Club in Central Square in Cambridge yesterday, she begrudgingly admitted that it was her first visit in months.

“I’m terrible, I know. I’ll be the one they’re pointing fingers at,’’ joked Pennewell, a 22-year-old public relations professional. “It’s just that the holidays came and work got crazy, so now I’m jumping on the bandwagon. This year I’m going to cook healthier and work out more than one month.’’

Health club memberships in the United States increased by more than 10 percent in 2010, to 50.2 million, according to the International Health, Racquet & Sportsclub Association, based in Boston.

More than 12 percent of new memberships are added in January. Yet the number of days members went to the gym declined by five from the previous year. Overall, health clubs reported just a 70 percent retention rate.

Many gym regulars said they think a part of the membership boom is motivated by sites such as Facebook, Foursquare, and Twitter, where new members love the backhanded brag of “checking in’’ at gyms or using apps that automatically share the number of miles they have run.


But there is a flip side, as well, for social media sites are also the home of the public gripe.

“I’ve noticed a lot of complaining about waiting in line for machines, locker rooms that are filled, parking lots that are full,’’ said Jessica Low, 25, who works in social media at Liberty Mutual and was on her way into the all-women’s Healthworks in Copley Square, where she is a regular.

But it is not all bad blood. Many of the regulars started with a resolution, and most of them stopped griping long enough to applaud the newcomers for making the attempt.

Fraser, who cannot find a place to jump rope, bought his girlfriend a membership for Christmas.

“So I guess I’m part of the problem,’’ he said.

But mostly, said Low, it is a question of “How long till I can get back to the machine I want at the time I want?’’

On Thursday night at the Boston Athletic Club in South Boston, Heather Foley was walking on a treadmill in a crowded cardio room, warming up before a run.

“This is twice as many people as there usually are on a Thursday. People are usually out boozing,’’ she said. “And there’s a Bruins game on.’’

Like most regulars, she looked at the unfamiliar faces with more than a bit of skepticism. “I want to say it’s great, that I support anyone making a healthy choice. But -’’


She looked around the room. “Let’s just say I’ll know in July what you were doing in January when I see you at the beach.’’

And if not . . . well, there is always next year.

Valentino, the manager at Boston Sports Club, said there are actually two types of regulars at his gym: those who come year-round and those who come, again and again, each January.

Billy Baker can be reached at billybaker@globe.com. Follow him on Twitter @billybaker.