Natalie Portman went the extra mile to prepare for her role in Black Swan

Natalie Portman turns 43 tomorrow and, despite such a long career in the industry, no role has pushed her to the limit like Black Swan.

The 2010 psychological horror follows Nina Sayers (Portman), a dancer who is passionate about being a ballerina.

Her dreams look to becoming a reality when an artistic director decides to put Nina ahead of his prima ballerina for their opening production of 'Swan Lake'.

However, Nina has soon faces competition from newcomer Lily (Mila Kunis).

As an intense rivalry develops between the two dancers, it soon turns into a twisted friendship and Nina's dark side unexpectedly emerges.

The role of Nina won Portman an Oscar in 2011, but it wasn't without a bit of sacrifice.

Not only did Portman mainly stick to a punishing diet of almonds and carrots, but she also trained for eight hours a day, seven days a week.

Pushing her body through a gruesome concoction of ballet, miles-long swims and cross-training, it’s no wonder the star dropped more than nine kilograms in the process.

Natalie Portman got into crazy shape for the film. (Fox Searchlight Pictures)

Former New York City Ballet dancer Mary Helen Bowers oversaw Portman’s ballet training and told Shape magazine after the film’s release: “We usually started by swimming a mile a day, doing the front crawl and breaststroke.

“Then we'd do 2 hours of ballet exercises and resistance work."

Portman also spoke candidly about the ‘extreme pain’ she put her body through when speaking to the Evening Standard back in 2012.

She explained: "The physical discipline of it really helped for the emotional side of the character because you get the sense of the monastic lifestyle of only working out, that is a ballet dancer's life.

"You don't drink, 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 you get that understanding of the self-flagellation of a ballet dancer."

The role won her an Oscar. (Fox Searchlight Pictures)

If her brutal Black Swan prep is anything to go by, then Portman no doubt found her routine for 2022's Thor: Love and Thunder a walk in the park.

When filming the Marvel movie in 2020, the actor opened up about her gym schedule during a virtual appearance on The Tonight Show with Jimmy Fallon .

Asked by Fallon: “Are you doing these crazy workouts and stuff?" to which Portman replied: "I’m trying!"

She added: "I’ve had like months of pandemic, eating baked goods and laying in bed and feeling sorry for myself.

"I’m, like, super tired after working out. And during. And dreading before.”