NEW YORK — January is for fitness centers what December is for retailers: a bad month makes for a bad year.

And with people spending less and less likely to overindulge this year, some in the fitness business are working harder to make sure they don't find themselves on the ropes.

"We're all kind of holding our breath," says Ben Quist, co-owner of Form & Fitness in Grafton, Wisc. He said while his club hasn't seen a decline in memberships, he is a little nervous. A third of the club's annual revenue is from new memberships in January, he said.

"You never take anything for granted," Quist said. "These next three months, I need to take in a handsome chunk of our revenue."

Historically, January is the single biggest month for new membership enrollment at health clubs, according to the International Health, Racquet & Sportsclub Association. Many fitness centers introduce some of their best deals, hoping to entice new members and lock them into a yearlong or even longer contract.

The number of gym memberships dropped 3 percent to 41.5 million between 2006 and 2007, according to the association. At the same time, the number of fitness centers is increasing.

There were 29,636 commercial fitness centers in 2007, up from 29,357 in 2006, according to the association. And in most big metropolitan markets, every commercial fitness facility has 10 to 25 competitive fitness operations within its prime target area, the association reports.

Health club memberships tend to skew toward those earning $50,000 or more, who are not the hardest hit by the economy, according to David Lockwood, director of research at Mintel, a market research firm.

But almost all consumers are cutting spending across the board, and for people with lower incomes, a gym is very likely a first cut, he said.

"We have to assume that the 'New Years' Resolve people' who join clubs en masse in January and others who do so for winter months will be fewer in number this year because of the economy," Lockwood said in an e-mail.

In part because of the economy, Curves International deepened its discount for new members, according to spokeswoman Kathy Carr. The original deal was 30 percent off and the first 30 days free.

Now, members who sign up between Jan. 1 and March 6 get 50 percent off the initiation fee, in addition to the first 30 days for free, said Carr.

Equinox Fitness Clubs, with locations in New York and Boston and other cities, are offering 50 percent off the initiation fee, plus a deal that if new members work out 36 times in the first three months they get the initiation fee back.