Rachel Weisz thought the most difficult part of starring in the 'The Bourne Legacy' was to stop running like a girl.

The 42-year-old actress portrays scientist Marta Shearling in the forthcoming action film, and she had to work hard to run in a more masculine way in scenes which see her alter-ego and lead character Aaron Cross (Jeremy Renner) attempt to avoid being hunted down and killed.

She told Britain's HELLO! magazine: ''I have to do a lot of running in the film and the hardest thing I had to learn was how not to run like a girl.

''Apparently, because women's hips are wider than men's it means our feet turn out when we run and I really had to work on that. It was difficult.''

Despite having a movie star for a mum, Rachel's six-year-old son Henry - from her previous relationship with director Darren Aronofsky - wasn't interested in watching her during filming for fantasy motion picture 'Oz: the Great and Powerful' because he has been around movies his whole life.

The brunette beauty - who is married to James Bond star Daniel Craig - added: ''He's not really interested. When I was shooting 'Oz', I said, 'Come and see me, Mommy's going to fly, want to come and watch?' and he just didn't care.

''That's fine - he has his own fantasy life, which is much richer than anything he can see in the movies. And why should movies be so special to him? His dad makes them all the time. And ... well, his stepdad is James Bond, isn't he?''