A typical Urban Rebounding class consists of five minutes of warm-ups, 25 minutes of choreographed cardio on the rebounder, 10 minutes of jogs, sprints and plyometrics (jumping exercises), 10 minutes of strength work and then a final 10-minute stretch on the rebounder. Christopher Blake Mays, a former Disney acrobat who teaches Urban Rebounding at Crunch Fitness, says it's possible to burn 700 calories in a 60-minute class. "I was drawn to it myself because I was looking for a fun workout that wouldn't hurt my joints," Mays says. People of all ages, even those with arthritis and pregnant women, take his classes. (Always consult with your physician before starting an exercise program.)

Jodi Lin Wiener, a 29-year-old fashion publicist in New York City, has been taking Urban Rebounding with Mays for more than two years. "I just love the fantastic rush I feel when I walk out [of each class]," she says. She even did an "Urban Rebounding marathon" this year to benefit the American Diabetes Association. "No matter how busy I am, I'll always make time for exercise," she notes. "But the opportunity to do something as enjoyable as Urban Rebounding makes going to the gym sheer delight." She also loves the effect this workout has had on her body. "When people notice that I've leaned up and lost weight, I tell them it has to do with rebounding," she says. "I love that you can do this exercise day in and day out because you never feel negative physical effects like you do with step, regular floor aerobics or kickboxing."