LOS ANGELES—Natalie Portman has been a movie star since she was 13 years old. However, it was the life she led just before she signed on to the movie The Professional that influenced her decision to take on what has probably been her toughest role. In Black Swan, which opens Friday (December 10), she plays a 28-year-old prima ballerina who suspects that someone wants to stop her from playing the lead in the iconic Swan Lake.

In an L.A. hotel room, Portman says she did ballet as a child and had always been interested in taking it to the movies. And although she’s managed to do that now, she admits that the ballet world depicted in the movie isn’t the one she saw through her lessons.

“I danced when I was young, until I was about 12, and idealized it, as most young girls do, as this most beautiful art, this expression without words,” Portman says. “I always wanted to do a film related to dance, and so when [director] Darren Aronofsky had this incredible idea that was not just related to the dance world but had this really complicated character, it was a great opportunity. I loved the story, and he is a director I would do anything for. So it was something completely exciting.”

Be careful what you wish for. The movie required months of training. Portman says that although she could see from the first reading of the script that it would be painful to find the character of Nina Sayers, she knew that if she wanted it to be an accurate portrayal of a modern ballet dancer, she was going to have to go places she hadn’t been before.

“It was a great challenge,” she says. “I had really great support from all of the teachers and coaches and choreographers who were shaping and pushing along the way, but I started with my ballet teacher a year ahead of time. She started very basically with me, but we would do two hours a day for the first six months to strengthen me so that I would feel confident doing more work and so I wouldn’t get injured. Then, later on, we did five hours a day that included swimming and toning and three hours of ballet class a day.

“Two months before we started shooting, we added choreography. So at that point we were doing probably eight hours a day, and the physical discipline of it really helped to find the emotional side of the character, because when you are doing the training, you get the sense of the monastic lifestyle of only working out that is the ballet dancer’s life. You don’t drink and you don’t go out with your friends. You don’t have much food, and you are constantly putting your body through extreme pain. So the training helped me to understand the self-flagellation of the ballet dancer.”

School helped as well. Portman has a B.A. with a major in psychology from Harvard and says she learned that the rituals of a ballet dancer’s life are somewhat similar to obsessive-compulsive behaviours. “Ballet lends itself to that because there are so many rituals, like the wrapping of the shoes every day and the preparing of new shoes for every performance. I think the process is almost religious in nature, similar to Catholics with their rosary. Their director [in the film, played by Vincent Cassel] is a godlike character, so it comes across as a devotional ritualistic art, which you can relate to as an actor because when you do a film, you submit to your director in much the same way. You devote yourself to them and you want to help create their vision.”

That vision may have been Aronofsky’s, but Portman was determined to find the diva at its centre. She says that she has always moved in and out of character with ease but realized early on that there were new risks in taking on a ballerina with the devotion of Sayers. She managed to eventually get back to being herself, and she says that Aronofsky got her through the tough parts.

“My approach has always been that as soon as I finish a scene, I am back to being me. I am not someone who likes to stay in character, but this film is clearly about a discipline that was going to lend itself to me being more like my character than past experiences. I was able to go back to my regular life afterwards, but one of the reasons I was able to do that was because Darren was as alert and disciplined and focused as I was. I am not a perfectionist, but I am definitely obedient. I work my hardest and try to be kind to everyone I work with, and that was the goal here: keeping focused on that and staying true to myself.”