Drinking too much champagne must cause spontaneous exercise. How else do you explain the annual boom in elliptical usage on Jan. 2?

But wait until the hangover wears off before you sign a contract for a new gym membership: There are a few factors that take serious thinking.

The big one is price, but that number isn’t entirely straightforward.

Sure, there are bound to be new year’s promos (and some December holiday specials, if you’re planning to get a head start), but the deals don’t have to stop there.

We’ve heard from plenty of gym members who have managed to negotiate a better price than the first one that’s offered. Clubs count on January to bring in massive business, so in this economy, you may find some willing to trim the enrollment fee or monthly charge.

It’s no bargain, though, if you don’t go. Think about location: A place that’s walking distance from your home might be worth an extra 10 bucks if it translates into extra gym time.

And really consider when and how you plan to exercise. The gym near your office might be awesome Monday through Friday, but what happens if you get a hankering for Zumba over the weekend?

And what amenities does a cheap gym have? A measly pool or a shortage of evening classes can be deal-breakers. What if you want personal training? Ask for schedules and quiz the management about staff credentials.

Sarah Lengyel, vice president for business development for Results the Gym, suggests looking for staff on the gym floor, preferably of the friendly, helpful and available variety.

“Some clubs have folks at the front desk and that’s it,” she says. And, of course, make sure the place is clean.

Don’t just peer from afar — poke around corners and pull back shower curtains. “There’s no worse feeling than signing up for a gym and knowing you’re grossed out by it. It’s hard enough to get there in the first place,” Lengyel says.

Be sure to swing by about the time you plan on doing most of your exercising. The resolution rush will make things crazier over the next few weeks, but that’s no excuse for not having enough equipment to accommodate the members.

Timing might also change the vibe of a place, as a gym can morph from Zen retreat to bumping nightclub to casual community center as the day goes by. See who else is there at your time and if you’d feel comfortable sweating alongside ’em.

And, of course, check what you’re signing up for. Some memberships are month-to-month, others are for a year or more, and clubs have very different policies on what happens if you move, change jobs or just want to cancel. The only traps you should have to be thinking about are your trapezius muscles.