Doing your own stunts. It's the mark of a truly studly actor. Tom Cruise and Russell Crowe do it.

And now you can add Renee Zellweger (search) to that list.

In her new movie, "Bridget Jones: The Edge of Reason," (search) the petite actress throws herself into the action. If that doesn't sound impressive, you obviously haven't seen the first Bridget Jones movie.

Playing the tragically clumsy (and totally adorable) Bridget has always meant a lot of tripping and tumbling over, since her whole character is about being embarrassed.

And in the new movie, the pratfalls are even broader.

The sequel, which opens Friday, picks up just eight weeks after the end of "Bridget Jones's Diary."

Our heroine is still with Colin Firth's Mark Darcy, the human-rights lawyer/perfect man that she bagged at the end of "Bridget Jones's Diary."

But the fairy-tale romance is already showing signs of strain (as you'd expect). Inside, Bridget still considers Darcy out of her league, and can't believe she got him. He has to tell her not to stare at him while he's trying to sleep.

Bridget keeps trying to impress Darcy and winds up in a series of ever-goofier misadventures that usually end with her falling flat on her face -- literally.

Though she's never skied in her life, she dons a silly pink snowsuit and rides the lift to the top of the Tyrolian Alps with Darcy, and soon she's flying down the mountain -- backwards.

Director Beeban Kidron had hired two stunt doubles to help with this scene, but in the end, Zellweger (who is actually a very excellent skier) did the stunts all by herself.

"She goes careening down the slope backward, with her bum in the air, and beautifully falls over at the feet of the other characters," Kidron recalls.

But that was nothing compared to the first scene in the film, when Bridget goes skydiving and winds up landing in a pig sty.

It was the first scene the 35-year-old Texan shot, and it put her in a very undignified position, especially for someone who won the Best Supporting Actress Oscar just nine months ago.

"At one point, I was lying flat in the pig poo in the pen," she says, recalling the moment when she watched a cameraman very carefully wipe some of the muck off his hands.

"I was like, 'Oh, Clive, did you get a mess on your hand?'" Zellweger recalls.

"And meanwhile, my cheek is right there in the feces."

Not that she really minded all that much.

"It was actually hilarious to me," she says. "And it kind of set the tone for the movie."

Despite all these adventures, the most impressive stunt Zellweger pulled for the second "Bridget" movie was gaining 30 pounds -- again.

For the original "Bridget" movie, Zellweger famously plumped up from a size 2 to a size 14 with a several-month diet of French toast, pizza, milkshakes and chocolate.

And, as anyone who reads the gossip pages knows, she lost the weight almost immediately after the movie wrapped. By the time of the 2001 Oscars, she looked almost skeletal in that famous yellow chiffon gown.

Zellweger's diet drama became juicy fodder for tabloid-magazine editors, to the actress's chagrin.

"It was so silly," she says now.

"The 20-doughnuts-a-day rumors, and the 'Does she look better Bridget-y or bony?' questions.

"I didn't understand the fascination with it. It's just my job. You're supposed to look like the characters you play, and that's all I was doing."

Zellweger was more concerned about how the yo-yo diet had affected her health - especially after watching the 2004 documentary "Super Size Me," in which New York filmmaker Morgan Spurlock gained 25 pounds on a month-long diet of nothing but McDonald's fast food.

"I never thought about it as a health problem or a potential threat until I saw that," Zellweger says. "I listened to doctors give him advice about stopping what he's doing immediately because of the severe long-term repercussions."

Given the risks, it should be no wonder that Zellweger took her time signing on to the second "Bridget Jones" movie, even though producers were ready to start right away.

Still, Zellweger insists she was reluctant because of artistic -- not health -- reasons.

"It took me some time to get comfortable with the idea of bringing the character back to life," says the star.

"Bridget is so special to so many people around the world that I didn't want to do anything that could compromise how people feel about her."

In the end, Zellweger came around and signed a reported $11 million contract to reprise her role.

But when she gained the weight this time, she consulted with a doctor who helped her do it as healthfully as possible.

Zellweger quit her rigorous exercise schedule last May and let her metabolism slow down for three months, then started eating a high-calorie diet with a lot of flaxseed-oil salad dressings and "delicious" protein weight-gain shakes.

By last October, when filming started in London, the 5-foot-3 actress had beefed up to 140 pounds.

But as soon as the shoot wrapped in January, she made a beeline for the treadmill.

"It feels good to finally go to the gym after nine months of not getting to," Zellweger told Oprah Winfrey just last week.

Ten months later, the actress is back to her normal weight, about 115 pounds, and the magazines are bashing her again.

Zellweger is also sporting long, brown and decidedly un-Bridget-like hair, which she grew for her latest role, in Ron Howard's drama "Cinderella Man."

When filming wrapped on "Cinderella Man" last month, Zellweger found herself in a very unfamiliar situation, without a new gig for the first time in four years.

"I haven't committed to do another film, and I'm not aggressively seeking one at this point," Zellweger says.

"It's essential. I need to collect some experiences as a person and not just as a person who's emulating someone else. I've been living in somebody else's apartment in somebody else's country, in somebody else's body.

"Now I just need to take a little time and be a girl.

"I need to go see girlfriends."

Not to mention a boyfriend -- Jack White, the 29-year-old indie-rock icon from the White Stripes.

The pair hooked up last year on the set of "Cold Mountain" and seem to have been together ever since, even though Zellweger steadfastly refuses to discuss the matter with the press.

"Yes, I know Jack White," was all she'd tell a reporter during a recent interview, adding only that "he is doing groundbreaking things" and that "I don't talk about that area of my personal life."

But this summer she was regularly seen around Detroit, where White lives, hanging out at his shows and partying with his friends.

And when Zellweger went on Oprah with "Bridget" co-stars Hugh Grant and Colin Firth last week, Grant accidentally let the cat out of the bag when he teased Zellweger on national TV that "your present boyfriend looks terrifying to me."

He's a "real hard-core kind of rocker," Grant added.

"I was introduced to him the other day and actually fled. I fled the room."

Grant babbled on for a while until he noticed Winfrey's amused face and Zellweger's shocked one and finally realized he was out of line.

"Oh, I'm sorry," he said. "I'm really sorry. I'm really sorry. It's not anyone. It was her assistant."

But the secret was out.

"Yeah," Zellweger muttered. "Thanks, man."