Katherine Jenkins and Mark Ballas

It's the best four semi-finalists we've ever seen. Graceful, powerful, athletic — and, except for one, broken. The level of competition this season on Dancing With The Stars is so high that the winner may be whoever still has two good working legs next week.

Classical singer Katherine Jenkins' back went out at the end of her second dance Monday night, the salsa, and she stood on the dance floor with her face in her hands, devastated. "Her leg gave out, and then her back kind of tweaked," says her pro partner, Mark Ballas, after the show. Why was she so upset? "I think it was a mixture of panic and pain," says Ballas. "I felt her slip, so I rolled myself under her and stood her back up so she wouldn't hit the ground."

After the show, Jenkins was being looked after by doctors. Though it's still not clear how serious the injury is, or whether she'll be able to continue, Ballas looked crushed. "We've had a good run. What a way to end it, huh?"

Maria Menounos, who has been performing with injuries from the beginning of the season — two broken ribs and severe foot strain verging on stress fractures — performed a near-perfect jive and then limped up the stairs to the skybox, holding her right leg. "I ripped something in my quad," she says after the show, holding on to pro Derek Hough so she could rip off her 3-inch dance heels and slip her ace-bandaged feet into fuzzy slippers. "I had a pain patch here on my thigh, earlier today.  But I couldn't wear it with my tango dress. And when we were standing there getting our judges' scores, I thought:  I think I'm gonna collapse right now." 

Latin heartthrob William Levy is just recovering from a torn ligament in his ankle. Only Green Bay Packer Donald Driver is injury-free. "He takes really good care of his body," says his pro partner, Peta Murgatroyd. "He'll work out before and after our rehearsals."

But, says pro Cheryl Burke, "We're all on the edge of having a physical and emotional breakdown. Dancing seven, eight hours a day, without a day off in months, it's not normal. It messes with your head, and it's really, really hard on the body."

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