London, Jan 18 (Agencies): Hollywood actress Natalie Portman has admitted she found the sets of her latest movie 'Black Swan' challenging because she never had an opportunity to relax.

The 29-year-old actress, who won the Goldern Globe Award for Best Actress for the role of a ballet dancer in the film, could not detach herself from the character due to the high amount of training that she had to undergo, reported Contactmusic.

"It was challenging, you know, I like to shut off the character as soon as I'd finished, whether that's finishing a take or going home for the day. It was really difficult because I had so much training outside of work to do.

"When work was done then I had to go to the gym, and then I had to get up at 5am and workout before. There wasn't really any time to just relax and be myself," said Portman.

The 'Closer' star, who met her ballet dancer fiancé Benjamin Milipied on the sets, found it tough to balance the demands of physicality with emotion and often ended up with her tongue hanging out.

"Balancing the physical with the emotional because sometimes just to do a certain move you need so much concentration, my mouth would be hanging open and I'd have a concentration face, it'd be all furrowed.

"Half the time they were trying just trying to get me to not have my tongue sticking out. And then to add on to that I have to be acting!" added Portman.