Tracy Anderson's vanity exercise

Tracy Anderson says vanity is the "most powerful motivator" when it comes to exercise.

The fitness guru - who is Gwyneth Paltrow's personal trainer and has previously worked with Madonna - claims that once women have seen how good they look, they will be determined to keep up their work-out regime because they feel so much better about themselves.

She said: "Everyone knows you need exercise to be healthy, but health is not enough. I have seen that vanity is the most powerful motivator, because once these women see what my method does for their looks, that's it. Then, because they see their bodies changing, their mind-set changes. They're in a better mood. Focused. They learn to love to sweat, to detoxify. They crave it.

"The boyfriends and husbands are angry when they first sign up, because its custom and costly, but then later they come to me saying not only has their wife never looked so good, but her confidence has changed their sex life dramatically. Women learn not to be afraid of using their bodies."

Tracy also says it's important for women to have some muscle because it improves their skin tone.

She told Style magazine: "You do need some muscle, because you can't have great skin tone without it - you just can't. I train a lot of models who did waif chic. You might be able to do the waif look by restricting food intake when you're 20, but when you're 60 and you haven't worked your muscles, your skin tone is gonna look like hell. It's like with Gwyneth. I would never want to bulk her up, but giving her some definition is sexy."