(Cover) - EN Showbiz - Emily Blunt says watching Natalie Portmans toned body in Black Swan give her an anxiety attack.

The Hollywood actress spent months in 2009 training to be ballerina for her film The Adjustment Bureau, a sci-fi thriller due out next year, and seeing Natalies physique playing a dancer in her movie Black Swan put pressure on Emily.

The 27-year-old has revealed that Natalies muscles made her jealous.

I had a full anxiety attack after it but still loved the movie," Emily said. "That girl has some serious guns. I was like, 'Wow, her back looks like a barrel of snakes.' She truly worked out and she looks incredible in the movie."

Black Swan tells the story of the relationship between a veteran dancer and her rival, whereas The Adjustment Bureau looks at an affair between a politician and a ballerina.

Emily admitted training for the role was crippling to her body and believes it is the hardest challenge she has undertaken yet.

However, the actress says the task was character-building and will benefit her later on in life.

"It's definitely an endurance test, learning how to be a dancer," she told MTV News. "That is some lifestyle. That is day in, day out, hours and hours and hours a day, just crippling your body. It was the hardest thing I have ever had to do in my life. I am so happy I did it because I think it's probably a good thing, soul-building, to do something every day that terrifies and embarrasses you. (C) Cover Media