by SIMON CABLE

Last updated at 00:23 02 April 2008

In one she is willowy, feminine and seductive.

In the other she has bulging biceps that would put many a he-man to shame.

As these two pictures of Madonna show, she can either change her shape at will - or the airbrush has been busily at work.

As she stepped out of the gym next to her London home yesterday, she showed an even more muscular and veiny upper body than usual.

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Slimmed down: Madonna, who is 50 in August, as she appears in Vanity Fair

Pumped-up: The singer emerging from the gym after a workout yesterday

While in a photoshoot for Vanity Fair to celebrate her half-century, appearing in only a basque, briefs and knee boots, she looked remarkably skinny and smooth by comparison.

Chris Bickmore, a top airbrush artist, said: "Obviously none of the veins on her arms are there. All lines and wrinkles have been removed. The same applies to her face.

"There are no marks or smile lines, which has made her look years younger."

Cover girl: Madonna on the cover of prestigious magazine Vanity Fair, out Friday

A Vanity Fair spokesman said retouching had been minimal - "just a little work on skin tones and blemishes".

Madonna, who is famous for her punishing exercise regime, works out for two hours, six days a week.

The pop star was joined by her pint-sized personal trainer and constant gym companion Tracy Anderson, whom she was referred to by best friend Gwyneth Paltrow.

Of the star, Tracy will say only: "It comes down to whether or not you are a hard worker and someone who puts in 100 per cent.

"I prefer to train with the dedicated and these women aren't afraid to work."

With her impending 50th birthday, Madonna seems more determined than ever to be in great shape, but her increasingly muscular appearance suggests she may be trying too hard.

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Coach: Madonna was joined by her personal trainer Tracy Anderson in London yesterday

Last month there was even speculation the image-concious star had undergone plastic surgery after she was seen with a bruised face and eyes.

The mother of three is currently preparing to embark on a promotional tour for of the release of her new album Hard Candy, which sees her duetting with Justin Timberlake.

Read more at www.vanityfair.com