Zoe Saldana says playing Nina Simone was a huge ''responsibility''.

The 35-year-old actress portrays the late jazz legend in an upcoming biopic, 'Nina', and despite facing criticism for not looking enough like the singer, Zoe felt the most important thing was to stay true to the memory of the iconic star, who passed away in 2003 aged 70.

She explained: ''I felt a huge responsibility and a lot of pressure to be true to her, to respect her legacy because she was real and so iconic and one of the most beautiful women to walk this earth.

''So in a way it was a difficult role for me. It was heartbreaking at times as it demanded a lot of emotional work and some days and becoming this person; to walk in her shoes was sometimes not a happy place to be.''

The actress has been able to work with great personal trainers thanks to her roles in action flicks 'The Guardians of the Galaxy' and 'Avatar' and has begun to associate keeping fit with her career.

She told Britain's HELLO! magazine: ''Recently I began to associate working out with work, so I took a break as I was tired. I swear by reformer Pilates as it gets you fit in a very balanced and healthy way because you use your own body weight.

''It can help back, knee, shoulder and hip problems, ease joints and get you in shape. Garrett Warren has been my stunt trainer in films for years; he gets me in shape for action roles, then I rely on Steve Moyer in LA who I met on 'Avatar'. They are my go-to trainers for life.''