Fitness classes follow fashion. The city’s gyms and studios constantly launch new “It” classes. In Class Action we dish on what we’re trying, or what we really want to. And please tell us what classes you’re excited about in the Comments section, below!

We love the fancy boutique fitness experience. But there are lots of less-expensive ways to get your butt kicked in this city, which is what I discovered after visiting the 92nd Street Y for a test run of one of their most popular group fitness classes: Bosu Bounce.

The cardio class revolves around use of a Bosu, which basically looks like a stability ball chopped in half, plus resistance bands. You’ll run on and off the ball, do squats, lunges, and crunches on it, slip your resistance band underneath it and work your arms, and even pick it up for a modified burpee.

The class is a hard, high-intensity workout, mainly because, just like the surfboard workout, you have to activate lots of muscles to stay on the damn thing.

It improves your balance and posture, says Sam Lopez, the class creator. “If you have rounded shoulders, an un-tucked butt, or you’re not tightening your belly button, you’ll fall off!” he says. He’s right—it happened to me.

And while the music stopped multiple times, and I had to clean grime off my Bosu before getting on, it was an overall good time. —Lisa Elaine Held

Who’s it for: The no-frills group fitness lover who likes a challenge.

Book it or skip it: Book it.

Visit www.92y.org for class times and locations. Membership at the 92nd Street Y’s May Center is $950 until March 31, and normally $1,275.