The initial appeal of hooping is that it's fun, but its lasting value is that it works. An hour of intense hooping can burn as many calories as an hour-long run on a treadmill. Exercisers can get a full-body workout with moves like HoopGirl's "pulse," which stimulates the entire core; the "limbo," which targets the back and thighs; and the "Wild West," which helps tone biceps and triceps. "Anything that gets people off the couch and burning calories is a good thing," says Pete McCall, an exercise physiologist for the American Council on Exercise. "Hooping can be a good way to mix up your routine and keep it from being boring."

"I could bend in ways I haven't been able to since I was a teenager," the Nashville-based star tells Shape magazine for its December issue (on sale Nov. 10). "My husband [Tim McGraw] loves it!" Her new routine is done with an instructor, and comes after years of waffling when it comes to working out. "I was always very athletic, playing basketball and softball and running track," she says.

"But in my 20s and 30s, I'd go through phases with exercise, working out for four weeks before a big tour or video shoot and not doing much afterward. Then I had three kids [with McGraw, daughters Gracie, 11; Maggie, 10; and Audrey, 6] and turned 40, so I decided to make a lifestyle change."

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In July she and McGraw began a daily routine that included four miles on the elliptical, light weight lifting, crunches and push-ups. "I found I slept better, had more energy and was stronger," says Hill, who then increased her regime to include Pilates classes three times a week.

"It was so hard, but ultimately so worth it. My core is much stronger, and my arms are more toned. In fact, wearing a bikini on a magazine cover is my 41st birthday present to myself."

Fitness experts estimate that less than 15% of Pilates students are men, but that number is growing rapidly as more men begin to see the benefits such training can provide. Many professional sports teams have added Pilates to their training regime -- as have well-known male athletes and celebrities (golfer Tiger Woods among them).

There are two basic types of Pilates workouts: mat workouts and equipment-based workouts. Mat workouts are often done in a class setting with little or no equipment and can be found at most gyms. These classes contain a variety of calisthenic-type movements with very specific instructions. Equipment-based workouts are usually conducted in private or in small group settings and use large machines that make the most of straps, springs and railings. Mat workouts are often included in gym memberships; equipment-based workouts usually cost extra.