Helen Hunt says her stark sex scene in her new movie 'The Sessions' is ''extraordinary''.

The 49-year-old stars as sex surrogate Cheryl in the real-life story of how she helped paralysed journalist and poet Mark O'Brien, played by John Hawkes, to lose his virginity.

She told Stylist magazine: ''Mark's disability is the thing that allowed the sex in this movie to be like the sex we all have; in a real way, rather than a choreographed, weird way.

''There's no fancy lighting and music swelling. It's just happening; it's kind of extraordinary.''

The emotional nature of its story made the film easier for Helen, ridding her of any embarrassment at showing full-frontal nudity.

She explained: ''I used Cheryl's desire to make [Mark] comfortable to balance the nerves.

''She wanted him to know she was comfortable with her body to allow him to think, 'Maybe I can be comfortable with my body.' That helped; that got me through.''

The film takes its story from 'How I Became A Human Being,' the autobiography of Mark O'Brien, who was forced to wear an iron lung for most of his life after contracting polio aged six.

It's a challenging role for Helen, who admits it is a definite departure from anything else she's done over her 40-year career.

She said: ''[Cheryl is] unlike any real person I've played before. And I've played a lot.''