Bob Harper

"The Biggest Loser's" Bob Harper (NBC UMV)

Bob Harper isn't going anywhere.

Season 11 of "The Biggest Loser" starts Tuesday on NBC with the biggest twist the weight-loss show has ever seen: Contestants must choose between working out with Harper and Jillian Michaels or with two unknown trainers.

Why would anyone choose the latter? Because it comes with four weeks immunity from elimination — the most valuable prize the show has to offer short of the $250,000 payday awaiting the contestant who loses the largest percentage of his or her body weight.

The introduction of the two new trainers — as yet unnamed, although the blogosphere is already buzzing about their identities — comes shortly after Michaels announced that this season will be her last. Which raises the question: What about Bob?

"People keep coming up to me and asking, 'What are you doing next?' and 'When are you leaving?' And my response is, 'I'm not going anywhere, there's still plenty of work to do here, folks!'" Harper said.

Contestants this season include Arthur Wornum, 34, a stay-at-home dad from Portland, Ore., who is the unhealthiest contestant ever. The 5-foot-8 Wornum weighs 507 pounds, and that's after losing nearly 140 pounds on his own. His body fat ratio dwarfs that of Season 9 winner Michael Ventrella, who was the single heaviest contestant at 526 pounds but stood over 6 feet tall.

Harper says Wornum represents a segment of the population that viewers haven't seen before — someone who is so morbidly obese he's nearly housebound. "Here's a guy who, even if he loses 100 pounds, still has 200 more pounds to go," Harper said. "So how do I keep someone like that motivated and focused … when they have such a long road ahead of them?"

This season will also see its most famous competitor yet: Olympic Gold medalist Rulon Gardner, who piled on the pounds after retiring from competitive wrestling. "I still can't believe what I did to myself," Gardner said recently. Harper said audiences will especially identify with Gardner: He followed a strict diet-and-exercise regimen for much of his career, but it was ultimately unsustainable, much like the overly strict diet that many Americans will adopt as they resolve to lose weight in 2011.

Don't do it, Harper warns. Instead, wake up each day and resolve to simply make better food choices and find ways to "move around more," he said. "If you trust in that process, and just focus on what you can do today, the rest will take care of itself."

What's less certain is what Michaels' departure will mean for the show. "The Biggest Loser" boasts devoted fans that have turned the series into a franchise that includes DVDs, CDs, cookbooks, a line of kitchen appliances, fitness wear, weight-loss resorts and more, but the show's ratings are off roughly 20% when comparing Season 8, which aired in fall 2009, with the recently completed Season 10. Nonetheless, it's one of the network's best performers.

"The show is at an interesting crossroads," said Brad Adgate, TV analyst for the advertising-buying firm Horizon Media. "It really depends on who they get to replace Jillian Michaels. She's not exactly Simon Cowell, but she's an important part of the show."

Executive Producer J.D. Roth said he's not concerned about the trainer shake-up. He said that although Bob and Jillian attained first-name-only, rock-star status among the show's fans, the "real" stars are the contestants who bare their souls and mirror the struggles of many Americans.

Harper said that he too is curious about how the two trainers will work out. "The worst thing they could do is come in and try to do what Jillian does." Audiences won't go for that, he said. The trainers need to usher in their own unique style. "We can't have screaming for the sake of screaming."

Michaels said that while she will always be indebted to "The Biggest Loser," she needs a break from the show that has consumed her life since 2005, and wants to focus on adoption and motherhood.

Harper, however, said he feels like he's just getting started, and joked about signing on through Season 30. In fact, it's not at all unusual to find him swinging by the ranch outside Los Angeles on a Saturday — even though it's a non-shooting day, and technically his day off — just to check in on the players.

"It just never gets old for me," Harper said.

'The Biggest Loser'

Where: NBC

When: 8 p.m. Tuesday
