Training for and shooting the boxing scenes for Clint Eastwood's Million Dollar Baby turned Hilary Swank into a rabid fan of the sweet science -- and it surprised her.

"In the beginning, it's not like I didn't like boxing," Swank says in a Los Angeles interview, "I just didn't think about boxing. And, when I heard about it, I just thought: 'What is the thing about hitting someone and getting hit?' The pleasure eluded me in the whole thing."

All that changed. Swank plays an aspiring female boxer in the Eastwood picture, which opens today as a bona fide Oscar candidate. That meant the 30-year-old actress from Lincoln, Nebraska -- who already has an Oscar as best actress for her stellar performance in Boys Don't Cry -- had to get serious about the sport she had long ignored.

Swank attended both men and women's bouts and got hooked. Meanwhile, she worked rigorously for months, training for four-and-a-half hours a day, six days a week, wolfing down egg whites, raw fish and protein shakes and bulking up from 110 pounds to a muscular 129 for the film.

"I lived, sleeped, ate, breathed, drank boxing," Swank says.

Some nights, she would wake and find herself punching her husband of seven years, actor Chad Lowe, as a reflex action.

"Like anything else in life," Swank offers, "when you have to dive into something deeper than you would (otherwise), you gain respect for it because you learn about it in some different way. I learned that boxing is so much more than anything physical. Obviously, the physical aspect of it is huge, but it such an unbelievably mental sport.

"It is so deep and it is really hard to explain, but I love boxing now and have an enormous amount of respect for boxers as athletes, because boxing is also the most physically challenging thing I have ever done. So getting to step in those people's shoes for that moment was amazing."

For Swank, the mental aspects of the role and of the story in the film were and still are more important than the boxing. While she jokes that Eastwood called the project "a female Rocky with a twist," the most serious part of the film involved mapping out a complex series of friendships in the film. Her co-stars, Eastwood and Morgan Freeman, both get involved with her character's training and ultimate fate -- as friends. The relationships are strictly father and daughter-like and platonic. But they are charged with emotion.

Swank says the film had her thinking about what makes her own marriage so rich and dynamic and lasting. She has known Lowe for a dozen years and they married in 1997.

"Obviously, sex is good," she says when that part of a relationship is mentioned. "Sex with my husband is great! Yeah!" But the real key, she adds, is a blend of three ingredients: "I would say communication and respect and believing in another person ... Because that makes you feel like you can do anything!"

That mental strength got her through the obstacles she faced in getting into a believable physical condition, a process that was both exhausting and exhilarating. "As my body started to get physically stronger, I felt so powerful -- and not in a 'I'll kick your ass!' type of way. But what happens is that you just realize your body is a machine."

The other challenge of the film is its challenging moral dilemma, says Swank. She cannot discuss the specifics without giving away the shattering plot twists involved. But she says that she does not have to agree with her character's beliefs on the issue just because she plays the role.

"Why I became an actress is because I love people and I love people stories and every person has a story -- every person. And it's my job to tell those stories, whether I agree with their stories or believe in that way of life.

"The great thing about it is that I get to learn a lot constantly about life and it helps me discover what I believe and what I don't believe, and that's always ever-changing because we grow all the time."