Kym Johnson and Mark Cuban, <EM>Dancing with the Stars</EM> Kym Johnson and Mark Cuban, Dancing with the Stars

Everyone talks about weight loss on Dancing with the Stars (tonight at 9 pm/ET, ABC), and for good reason. If you stay in the game long enough, the long hours of practice — some are putting in as many as six hours a day — can't help but whittle away any extra pounds and inches. Marie Osmond is over the moon about losing 3 inches from her waist. Jane Seymour, who has lost 16 pounds, is glowing after hearing that people at the show were comparing her new body to one of the exceptionally beautiful and streamlined pro dancers. "Everyone's calling me Edyta today," says Seymour, referring to Cameron Mathison's (All My Children) partner, Edyta Sliwinska. "And I'm loving it. Can you imagine?"

But this season, because so many of the celebrities have been physically challenged by their health histories, the focus is not only weight loss but their new feeling of well-being. "Lots of the dancers this season have suspect body parts," says Dancing executive producer Conrad Green. "We had Wayne Newton's bad knee. We've got Cameron Mathison, who had trouble with his hips as a child. We've got Jane's bad back. And Mark Cuban [who had a hip replaced at the end of June]. If Heather Mills [who danced last season on a prosthetic left leg] and someone who's just had a hip operation can dance, then anyone can dance."

"You can't believe the difference in my mobility," says Cuban, who looks thinner every week and cruises the Dancing hallways like a sleek panther. He shows no trace of the arthritis that was crippling his left hip. "I was so crooked before because I was compensating for my hip," says Cuban. "For a couple of years before the operation, people would ask me why I was limping and I didn't even know I was doing it." He knows he's rushing the rehab, but Cuban thinks dancing is the greatest physical therapy in the world. "I feel like I'm 21 again. People walk by now and don't even recognize me."

Mathison says his hips have been very tight but he ices them every night and the dancing workouts actually ease his discomfort. He suffered from a childhood disease that forced him to wear braces for several years. As an adult, he feels no ill effect, except the stiffness he's lived with his entire life. "Once I get stretching, I'm fine," he says. "And my hips have been getting better and better."

Seymour has spent years trying to protect her sore back. She was taken in for an emergency herniated-disk operation six years ago. Now, her pro partner, Tony Dovolani, is an exceedingly proud teacher who wants to show off his student's new physique. "Look at this," he tells you, turning Seymour around and pointing to her lower spine. Seymour, Dovolani and her doctor got together before she started training for the show, all concerned that she not do further injury to herself. "She had no muscle on the left side at all, and now, look, there is equal definition to the muscles on both sides. We straightened her out and strengthened her back. We've created a new back!" Seymour is thrilled. "It doesn't matter what happens on the show," she says. "Because I've already won."

Even world champion boxer Floyd Mayweather is showing changes from dancing. His weight hasn't changed, but his manager, Leonard Ellerbe, says he's noticed changes in Mayweather's posture. "He's standing up straighter, I have noticed that," says Ellerbe. Mayweather puts in the most punishing training schedules of all the celebrity dancers. "He was in the gym at 4 o'clock this morning, training for his December fight," says Ellerbe. Because of his added practice hours on the show? "No, that's what he usually does," says Ellerbe. "He's always done that. He thinks like this: 'What are my competitors doing at 4 in the morning? Sleeping. That's why I'm gonna win.'"

But Ellerbe says that Mayweather has been so impressed by the dancing workouts — and the effect the show has had on his fans — that he's thinking about opening up a dance studio for kids in his hometown of Grand Rapids, Michigan. "People are talking to him about the dancing all the time," says Ellerbe. "And the kids look up to him so much. If they see Floyd dancing, they figure it's OK to dance. So he wants to do something to help them."

Grand Rapids is one of those Michigan towns feeling the pain from the ailing automotive industry. "The parents are calling me up now all the time," says Ellerbe, "asking me how they can get their children involved in dancing."

After all this talk about good diet and wonderful exercise regiments, it's refreshing to see Edyta Sliwinska — in her bathrobe — at the backstage crafts services table, wolfing down corn chips. You'd think her diet would be perfect, but she begs to differ. "I have to have sugar or I'll crash," she says. "I want some of those sour gummy bears right now."

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