Beauty

When it comes to exercise, interest tends to be exhausted long before stamina. If you do the same routine repeatedly, your body learns how to complete the exercises more efficiently, and results will be ever more elusive. That's why it's best to keep finding new forms of exercise and integrating them into your workout. Ari Nunez has evolved her Gotham Box at Equinox into a less flailing, more controlled martial-arts-based class that allows you to work through your muscles, which means a leaner look and probably fewer injuries. Moves include kicks, punches, pliés, lunges, and those froglike plyometric jumps that really elevate the heart rate. By the end of the hour, there's not a dry T-shirt in the room.

Nancy Hirsch and Greg Cook at Crunch
1109 59th Street
212-758-3434

At Crunch, a class on mini-trampolines called Rebounding has really taken off. Both Nancy Hirsch and Greg Cook incorporate exhilarating choreographed moves and jumps on the trampoline with weight and floor work. The rebounder, not your legs, absorbs the shock, and the vertical motion pumps lactic acid out of your body, so there's less discomfort after a workout. The one drawback: It's getting so popular you'd better get there early or you won't get a trampoline.