Biggest Loser' Trainer Jillian Michaels Worries for Contestants' Medical Safety

'The Biggest Loser' trainer Jillian Michaels is about to face her most difficult challenge this season. The show's producers are bringing the biggest contestant ever to the show: Michael Ventrella, who weighs in at 526 pounds. His size and the size of other contestants this year has Michaels worried.

The tough-love trainer shows her concern for the contestants' medical safety. "The contestants keep getting bigger and bigger," Michaels tells Ladies' Home Journal. "As the trainers we have no say over the challenges. We worry about them too."

Last season, contestant Tracey collapsed after valiantly trying to finish a one-mile run with the other contestants. Turns out, she suffered from heat stroke. Dr. Robert Huizenga explains that because of the amount of body fat, her body holds onto heat too efficiently and can't cool off. Tracey's collapse put the show under much scrutiny as viewers and medical professionals wondered if 'Biggest Loser' had gone too far.

The show's executive producer Todd A. Nelson says, "We all worry," but adds that the show is learning how to safely manage the medical conditions of the heaviest contestants, "and this allows us to fine-tune the process and reach out to a heavier population."

But the show will go on -- with the heaviest contestants yet, says Michaels.

As the show's new season kicks off Tuesday (8 p.m. EST) on NBC, Michaels reveals that it's a whole lot more work than anyone sees on TV. "You never see what's going on in its entirety," she says. "For every 10 minutes we're on the show, acting like insane people, there are a hundred hours of training you don't see. The stretching, the icing. Nobody wants to watch that."

"I'm passionate about helping people rebuild their lives," she says. "When someone feels strong physically, they feel strong in every aspect of their existence. If they have endurance and achieve in the gym, then I can redefine their entire self image. I can wipe away years of negativity."