Toymaker Wham-O's Hula-Hoop may be 50 years old, but the quintessential suburban-sidewalk pastime has reinvented itself as a core-tightening workout that's actually fun.

"The hoop can teach you to move more freely and creatively—most of us don't have a lot of opportunities to throw our hips around like that in everyday life," says San Francisco hoop instructor Christabel Zamor, author of the new book Hooping! A Revolutionary Fitness Program. What's more, you can burn 300 calories in a half hour of vigorous hooping.

Experienced hoopers effortlessly move the hoop up and down their bodies, twirling it along their arms, even jumping in and out as it spins. If you're struggling to keep a kid-size hoop around your middle, there's hope: "Put one foot forward and keep both feet planted on the ground, then rock your hips front to back instead of side to side," Zamor suggests. "But your best option may be a larger hoop, which you can order online—they're easier for adults to keep going." (Visit Sports-Hoop.com for a variety of sizes.)