Seeing how Cosmic Book News reviewed Black Swan, I thought I would give this a gander.
There is a bit of controversy regarding just who did the dance steps you saw in the Darren Aronofsky directed movie.
Portman has been credited with giving a stellar performance, winning an Oscar for best actress, with reportedly doing up to 85% of the required moves.
According to an article from EW, Portman's dance-double, Sarah Lane, was the one dancing.
Sarah Lane, of the American Ballet Theatre, claims she was the one you saw in the full body shots, with Portman's face digitally imprinted on her own, and that Portman's finacee and choreographer, Benjamin Millepied, has been lieing to the press in regards to how much Portman really did. Lane spoke up as a result of Millipied telling the LA Times that Portman was the one doing the work - in reponse to various articles stating Lane did.
“They wanted to create this idea in people’s minds that Natalie was some kind of prodigy or so gifted in dance and really worked so hard to make herself a ballerina in a year and a half for the movie, basically because of the Oscar,” says Lane. “It is demeaning to the profession and not just to me. I’ve been doing this for 22 years…. Can you become a concert pianist in a year and a half, even if you’re a movie star?”
“I mean, from a professional dancer’s standpoint, she doesn’t look like a professional ballet dancer at all and she can’t dance in pointe shoes. And she can’t move her body; she’s very stiff,” says Lane. “I do give her a lot of credit because in a year and a half she lost a lot of weight and she really tried to go method and get into a dancers head and really feel like a ballet dancer.”
EW notes Portman has stated that she did use a body double for the difficult sequences, but nothing to suggest that Lane did this much.
Lane also comments that she was told to downplay her involvement with the press and wasn't too happy with the credits she received on the film - which basically amounted to zip.
There is even the following video which shows how they added and changed various effects in the movie.