An Oscar winner for her performance in Cold Mountain, Renée Zellweger also won a legion of fans for her performance as Bridget Jones in two hit movies. Since her breakthrough role as kind-hearted Dorothy Boyd in Jerry Maguire nine years ago, the 36-year-old Texan has appeared in such diverse fare as Nurse Betty, Me, Myself And Irene and the musical Chicago. In Ron Howard's Cinderella Man she plays Mae, loyal wife to heavyweight boxer James Braddock (Russell Crowe) during grim times in the Great Depression of the 30s.

What research did you do on the life of Mae Braddock?

There was so much material, we were spoiled in that respect. Ron has a particular fascination with this period in American history so there's not much about it that he doesn't know, or doesn't find interesting. To walk into his offices in Toronto was to walk into a library about that period in the United States. I mean, on the walls, everywhere, were images that I'd never seen before. Compilations of first hand accounts of what it was like to live at the time, film footage, newsreels, radio interviews and of course the personal effects of the Braddocks everywhere. And one of the actors in the film, Rosemary DeWitt, is actually the grandchild of the Braddocks. She brought so many beautiful things that we wouldn't have been privy to otherwise.

Is Mae a woman you came to like the more you got to know about her?

She was an elegant woman with such strength of character to be facing such adversity and yet managing to maintain her composure for the sake of her family. I did admire her the more I came to know her. She had this impish kind of joy that was just beneath the surface, but she was also very elegant and reserved. It was a very introverted sort of characterisation, quite different from what I had done before. I found her fascinating.

What does it add to your performance when you're sparring - as it were - with Russell Crowe in key dramatic scenes?

As an actor, when you go to work, and you sit in the scene in the room and you're working with everyone cooperatively, the least you hope for is that you tell that bit of the story. You've moved it along, you've kind of done your job. But what's rare and sounds really weird is that every now and then the experience transcends whatever's going on in the room. Whatever you're animating, or re-animating, at the time becomes the reality. And it is extraordinary. That happened a lot with Russell because he's there, so you want to go and join him in that place. It's a bit like the writer who doesn't realise that the sun's gone down outside and that he's been sitting there with his pen in his hand for 12 hours. It's that: it's when that focus doesn't break and the creativity just flows.

What, for you, is the difference in playing real characters as opposed to fictional ones?

The responsibility is slightly different in terms of accuracy. You always want to be sure that you don't drop the ball for your co-stars in any case, but in this case there were also Mae's family members and the people who knew her.

When did you first learn about this story?

I read the script in about 1997, I think that's when Russell had it in mind that he was going to get the movie made. I loved it and knew that it was special, not only because the content was so moving but because it was a true story and you didn't have to talk about sensationalising that. These people lived and this was their life story and what it came to represent was a phenomenal hope for an entire generation. They don't make movies like that any more, but those are my favourite kinds of films.

Cinderella Man is released in UK cinemas on Friday 9th September 2005.