MADISON, Wis. -- About the time that New Year's resolutions start to wear off, the thought of wearing a summer swimsuit snaps nearly everyone back into their fitness routine.

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Fitness experts said if the treadmill isn't cutting it anymore, it might be time to sign up for a class.

At Bally's Total Fitness, instructor Eddie Carrington gets his clients in shape with Kwando, a full-body workout.

"It's focused on different martial arts," said Carrington.

He also teaches a hip-hop dance class, which he called a cardio powerhouse because of the fast beat and nonstop movement.

"Because it's so fun, they forget that they're working so hard," said Carrington.

Many gyms are also offering fitness classes in African dance, or a military-style workout, WISC-TV reported.

"It's hard core with lunges, squats, squat thrusts and push-ups," said Kevin Creegan of Crunch Fitness.

A newer exercise from Russia is also swinging into health clubs. The class uses a weight called a kettleball that the Russians have used for 200 years to train their top athletes.

"You're winded after 20 swings," said class participant Diane Baird.

"It's probably the most efficient workout that I've come across," said personal trainer Kathleen Aicardi. "It combines cardio, core and strength training all in one."

Belly dancing is also catching on as a fitness craze.

"You're working everything, your legs, your arms, your core, your back," said instructor Oreet Sharqui.

Fitness experts said shaking up an old routine is the best way to maximize weight loss before the summer.