Get off that boring old treadmill and belt out a cheesy Elvis song on the exercise bike, instead. Strut around in 3-inch heels or work up a sweat on the pogo stick.

As gyms compete with dance studios and adult sports leagues to hold on to members with ever-shorter attention spans, run-of-the-mill aerobics and other classes are getting an injection of creativity.

So, sessions like "Karaoke Spin," "Pogo Bootcamp," and "Stiletto Strength," are springing up in gyms across the country.

"People are putting in longer hours at the office," said Donna Cyprus, who's in charge of programming for Crunch Fitness. "The gym shouldn't be another chore."

But, increasingly, the fitness-conscious view it exactly that way. Since 2000, the average length of a gym membership has dropped from 5.7 years to 4.6 years, according to the International Health, Racquet and Sportsclub Association.

"With so many more clubs, it opens up opportunities for people to leave and seek a better alternative," said Brooke Correia, the industry group's spokeswoman.

Just learning to pronounce the names of exotic classes like "IntenSati" (in-TEN-SAH-tee) and "Budokon" (boo-DOH-kahn) at New York City-based Equinox can take some flexing.

An hour on the stationary bike, by comparison, might seem like a chore.

The classes at Bally's Total Fitness are more predictable -- yoga, Pilates, aerobics. But the Chicago-based chain plans to add options like African dance and Brazilian martial arts by early next year.

"One of the reasons is so we can attract a broader, larger membership base," said Norris Tomlinson, the company's director of group exercise.

For gym members, a hip-hop dance or kickboxing class has a physical benefit besides the mental advantage of staying fresh. People are more likely to flex different parts of the body while learning new moves, lowering the risk for injury, said Richard Cotton, spokesman for the American Council on Exercise.

"You're not walking up and down the same steps, stressing the same muscles," he said.

Working out with others also builds camaraderie, making it easier to commit to regular exercise, he said.

To avoid gimmicky classes with no physical benefit, Cotton said to look for classes that combine moves that build strength, improve flexibility and increase the heart rate for at least 20 minutes.

Group classes -- typically freshened every few months with new moves and music -- have long been a big draw for gyms. Most of the nation's 29,000 health clubs offer some type of group class, according to IHRSA.

"It's what keeps people coming back," said Carrie Kepple, director of programming at Gold's Gym, based in Irving, Texas. "When there were only a couple classes in clubs 10 years ago, people got bored and their bodies would plateau. Nowadays, classes are geared toward allowing choices and tricking bodies into getting a workout."

About half the members at Gold's Gyms renew their memberships after their first year. Among those who take a class, the renewal rate is 75 percent.

Group classes are the "meat and potatoes" of Crunch's business too, Cyprus said, with about 60 percent of members taking a class, and a third of those regularly experimenting with new ones.

"It's stimulating," said Harold Fyvie, who took up Brazilian jujitsu at Excel 180 in Albany, N.Y., four months ago.

Fyvie has joined gyms in the past, but inevitably lost interest after a few weeks. With jujitsu, he's lost 20 pounds in four months and doesn't see himself quitting anytime soon.

"It's always going to be a challenge," he said.

Other gyms might tailor their classes for different groups.

At Albany's Excel 180, owner Joseph Cox said he started offering Brazilian jujitsu to attract more men, who might feel silly signing up for a yoga class.

It's been so successful he's rolling out a new class this month: tai chi.

This time, he says, the hope is to attract older members who might be looking for a gentler workout.