The ever conscious world of celebrity appears to have fallen victim to a new addiction, and this time it's not illegal.

Madonna appears to be one of the key members at the forefront of the trend for punishing workout schedules.

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Bony Madge: Madonna's intense fitness regime has resulted in supremely low body fat revealing every bulging vein and a bony frame

But it appears the results are less than pleasing to the eye, as the singer regularly exhibits intensely veiny hands, and pumped up forearms which would not look out of place on a professional bodybuilder.

The 49-year-old's fear of getting older dictates her vigorous fitness drive. She begins her punishing routine with a three-hour session of Ashtanga yoga, followed by a Pilates session before lunch.

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Uber-muscular: Sex and the City star Sarah Jessica Parker's exercise regime includes running, climbing stairs and yoga. But she says she'd rather go to a dinner party

She then alternates her third daily session between karate, pumping iron, running, swimming, cycling and occasionally horse-riding. Fitness expert Cornel Chin said: "She clearly works out with weights to define her muscles."

Renee Zellweger drew gasps at the Oscars as the actress famous for her role as curvy fictional heroine Bridget Jones revealed her knobbly shoulders in a strapless evening gown.

Following her role as the big-pant wearing character, 38-year-old Renee shrank to a shocking size zero on a macrobiotic diet of lean fish, rice and vegetables, as well as enduring a gruelling two-hour daily workout with her personal trainer to shed all traces of rotundity.

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Me and my biceps: Tara Palmer-Tompkinson hates her bulging biceps which would put many a man to shame

Renee also did a lot of running, hiking, yoga and swimming. The actress said: "I like fun exercise. But I need physical exertion of the sweating kind. I go for a run. That's my thinking time. That's where I get it out, any frustrations or whatever."

But judging by recent pictures of her, it looks as if she's taken her exercise habit too far.

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Gym bunny: Superfit Nell McAndrew shed 2st by running, cycling and swimming after the birth of her son, even going for a run after her 6.30am feed

Bony: Renee Zellweger, here last year in LA, also has protruding muscles due to extreme exercise

Sex and the City star Sarah Jessica Parker has attempted to downplay her daily exercise timetable claiming she's more inclined to "go to a dinner party than slave away in the gym" but it's clear the mother-of-one doth protest too much.

The actress often reveals her bulging veins and sinewy arms in the designer gowns she loves wear.

Enviable though her slim figure may be in her red carpet frocks, her tough daily exercise regime of running, climbing stairs, yoga and Pilates has left her looking scrawny and leathery, and prematurely aged.

Richard Cormley, a personal trainer in Kensington said: "Sarah has obviously done high-resistance training to get her arms sculpted. She has a low body-fat percentage – you can tell by the definition on her arms – and she has started to develop chest muscles."

The pressure for A-listers to stay extra slim for their starring roles appears to have crossed the Atlantic, as British celebrities fall victim to the over-exercising trend.

Tara Palmer-Tompkinson, 36 has always been naturally slender. Recently though she's displayed uber-defined biceps that she hates but any man would be proud of.

"I tell my friends I'm on the doughnut diet, but I can't put the weight back on. If I went to the gym I'd bulk up. I hate my muscles. They're all very veiny", said the socialite.

Harley Street surgeon Apostolos Gaitainis said: "She may be genetically prone to having large veins, but this appears to be a result of overtraining. There is no fat to disguise them."

And marathon runner Nell McAndrew has been a self-confessed exercise bunny for years. The 34-year-old mother of one admitted: "When I feel blue or things aren't going well for me, I go running or take to the gym.

"I cannot imagine my life without exercise. It helps me to think positively."

Just six months after the birth of her baby boy Devon, Nell shed 2st by cycling, walking and swimming. She even went for a run after her baby's 6.30 morning feed.