When Renee Zellweger showed off her super-toned frame at this week’s “Fashion Oscars” in New York, her muscular back was almost as much of a talking point as the fabulous dresses.
After all, this is the same Renee whose weight fluctuates nearly as regularly as she takes on new film roles.
The slender actress famously embarked on a 4,000 calorie-a-day diet to load on 20lbs in just a few months to play Bridget Jones (twice) - then, as swiftly as she gained the curves, her weight plummeted to a sinewy size zero.
Meanwhile, her turbulent love life has also caused her weight to drop dramatically. But this week, she was looking sleek and toned as she stole the show at the Metropolitan Museum of Art Costume Institute Gala in a backless gold Carolina Herrera gown.
So just how does the 42-year-old actress achieve her extraordinary physique - and would you really want to get the same muscly results? After all, numerous surveys have revealed that men prefer a curvy size 14 woman to a super-skinny size zero.
Here, we give you the run down of her gruelling diet and exercise tips ...
You don’t get a body like Renee’s by sitting on your bottom, and the actress admits she has to stick to a strict routine to achieve her toned physique.
Since hitting 40, Renee has honed her super-firm figure and those amazing legs with gruelling two-hour workouts, six days a week.
She’s also a running devotee who covers a minimum of three to six miles every day, happily admitting that she’s addicted to the “runner’s high”.
When running in the gym, Renee watches television to keep herself entertained while clocking up the miles, including regular sprint intervals on a treadmill.
However, Renee admits that she does sometimes have a tendency to overdo it. Despite problems with her hip and being warned by her doctor to stop, she says: “I run until it hurts.”
Nor does she let travelling or a busy schedule get in the way of her workouts, confessing: “Wherever I move, wherever I’m stationed or whatever phase of life I’m in, the gym is my common denominator.”
As well as running, Renee uses hiking, swimming, yoga and cycling sessions to tone up her bottom, thighs and, of course, those fabulous calves.
To prepare for her role as dancing queen Roxie Hart in the film of Chicago, she was in the gym every day working on her stamina.
She admitted: “I was using muscles that I never knew I had.”
Fitness expert Iain Reitze, of prestigebootcamp.com, says: “Yo-yo dieting can be very dangerous for women and cause long-term damage to their health.
“It can raise blood pressure and possibly lead to heart disease, while starving then bingeing can impact mood and self-esteem.
“The best way to maintain a healthy, fabulous figure is regular exercise and a balanced diet.
“But unlike Renee, for most women, a two-hour workout every day is not realistic. Build cardio into your day by walking or cycling instead of driving, where possible.
“Or try to sprint on the spot as hard as possible for 20 seconds then rest for ten seconds and alternate this repeatedly for four minutes, twice a day.
“This high-intensity exercise can be as effective as Renee’s daily three miles, as it pushes you to maximum strength, increases your heart rate and is just as good as running for miles. It will also increase your metabolism, so you continue to burn more calories throughout the day.”
Weight-training is the most important secret weapon behind Renee’s super-toned back and arms.
While the star is notoriously secretive about her exact regime, experts say it would be impossible to achieve this shape without some serious dedication to working out with weights and the help of a committed personal trainer.
“Renee has very defined latissimus dorsi muscles, which are what give her the V-shape that makes her back muscles appear wider at the top and narrower at the bottom,” says Iain Reitze.
“She’s worked out intensively to achieve this look. To get this defined shape safely, focus on the back muscles at the gym by doing pull-downs using a weight machine.
“To shape the top and sides of your back, try the lateral raise technique, holding dumbbells and raising your arms outwards to shoulder height.
“If you don’t have dumbbells, a baked bean tin will work. This creates the round shape to your shoulders.
“Great arms like Renee’s also require serious attention to both your biceps and triceps.
“The triceps are located at the back of the upper arm and are used whenever you push something, i.e. a baby pram or shopping trolley.
“The biceps, located at the front of the upper arm, are used for lifting light objects.”
Famous for her fluctuating weight after piling on and losing the pounds for the two Bridget Jones movies, Renee has previously been a devotee of the Zone Diet - which involves eating a 40:30:30 ratio of carbs to fat to protein.
She has also been rumoured to have tried the Atkins Diet, the strict eating regime famous for shunning carbohydrates.
To achieve her post-Bridget Jones rapid weight loss, Renee’s meals were mainly tuna or cold meat coupled with dressing, salads and raw vegetables.
Currently, Renee is reported to be following a macrobiotic regime of fish, rice and vegetables.
Macrobiotic diets consist of low-fat, high-fibre foods, with grains typically making up about 50 per cent of each meal.
These diets might not sound like much fun, but Angela Walker, nutritional therapist at the London health clinic Fabulous Nutrition, says they are nutritious.
“A balanced diet is crucial for keeping your muscles defined and a macrobiotic diet is very effective at this. But - as with all restrictive diets - you need to be careful about skipping food groups.
“The amino acids in proteins, such as fish, eggs and meat, really help to build muscle, so it looks to me like Renee’s been eating lots of these to achieve this sinewy look. Her slim frame also suggests she has been restricting her portions.
“Eat plenty of well-sourced, organic proteins, leafy vegetables and whole grains, such as brown rice, in combination with exercise if you want to get a similar silhouette.
“But always be careful to eat a wide variety of different foods to get the best possible mix of fatty acids, vitamins and minerals that your body needs to function healthily and effectively.” - Daily Mail