When they want to tone up, Marisa Tomei, Liv Tyler and Beyonce Knowles go for a spin.

They pick up a hula hoop, that '50s and '60s staple that's twirled around the waist, limbs or neck. And courtesy of the fitness-extolling efforts of first lady Michelle Obama, plus the endorsements of various A-listers, this basic, no-frills childhood toy is making a comeback in the ever-changing world of fitness.

Last week during a White House event promoting healthful living, Obama showed off her hula hooping skills. "We don't just want our kids to exercise because we tell them to. We want them to exercise because it's fun and they enjoy it. And we want them to learn now how to lead good, healthy lifestyles so that they're not struggling to figure out how to do that when they're older," she told parents and kids.

Celebrity fitness trainer David Kirsch expects that after Obama's public whirling, "hula hoops will start flying off the shelves. The fact that she is the living embodiment of health and wellness in a very real and accessible way sends a very powerful message."

Sure, Obama's spin of approval is a good thing. But that aside, hula hooping has exercise benefits. "It engages the core and the butt and hips. It's a little bit of cardio if you do it long enough," Kirsch says. "It's full-body. It's cheap, fun, portable and engaging — and you can do it with your kids."

Knowles has been whirling since childhood. And Oscar-winning actress Tomei never leaves home without her hoop.

"I bring one to all sets now. You're waiting and you have all that extra energy and you want to stay focused and relaxed, and something about that hoop — you do it and it calms you down," she says.

Her green hoop sits in the living room of her Manhattan apartment. "Someone gave me a hula hoop two years ago. It feels really good, and it's really calming. Honestly, it's the best thing. It massages your organs."

Kirsch's longtime client Tyler also hoops, because "it's something she can do with (her son) Milo, and she likes to move. It's not like doing bicep curls and crunches. They're effective and good for us, but they're boring. She wants to get outside."