Hilary Swank exercises to see how far she can push her body.

The 'Million Dollar Baby' star always makes time for her work-outs because she considers it as essential as eating or breathing.

She said: "I love getting the opportunity to recognise what your body's capable of. Being an athlete is something I enjoy. I don't even think of not exercising. It's like the air you breathe and the food and water you need."

The 35-year-old beauty says she was inspired to work out more after becoming mesmerised by the muscular form of African tribe members.

She explained: "You see these incredible bodies in Africa that are all muscle. They're running to hunt in these tribes. And you think: 'How does the body look like that?' But if you're utilising your body, you recognise it is a machine and it can be capable of whatever you need it to be.

"Maybe there was a point where I was a perfectionist. Probably up until I reached my thirties. I do set big goals for myself and push myself very hard but there is no such thing as perfection. You'd drive yourself crazy."