Good news for those people who equate slouching with the moral disintegration of the nation and the abrupt rise in crack-addled toddlers. Good deportment, once the preserve of prissy finishing schools, has made a last-minute entry onto the most fashionable wish lists, sliding in alongside cashmere ponchos and younger-looking skin.

The spiralling popularity of yoga (see Madonna's arms and all of Gwyneth Paltrow) and trendy movement classes such as Pilates, the Alexander technique, the Norris technique of body alignment and the Feldenkrais method, speaks volumes about an increasing concern with the way we stand and walk. The young and hip, who once embraced the slouch as the last word in yawning ennui, are having to reconsider their position.

As for the rest of us - who know the slouch as the inevitable conclusion of a day spent slaving over a hot computer with a telephone tucked un-ergonomically between chin and ear - well, it's only a matter of time.

Fashion harpy sensibilities aside, the importance of good posture is gaining increasing credibility on medical grounds. On Sunday, BackCare (formerly the National Back Pain Association) and the TUC launched National BackCare Week with a report claiming that back strain in women employees costs this country 44m working days a year. According to Dr Peter Skew, GP and BackCare patron, between 60 and 80% of the population suffer from back complaints, and bad posture both results from these problems, and exacerbates it. "Back pain has become so common, it's virtually normal," says Skew. "Abnormal posture will only accentuate back pain."

Physical therapist Deborah Ellison agrees. "Most aches, pains and non-contact sports injuries are related to postural imbalance," she says. "The most common of these imbalances is a forward head posture, often with rounded shoulders."

Postural problems tend to kick in the moment an individual embraces desk culture. Sitting is second only to the common cold as the reason for lost days at work. "Children tend to have good posture until they reach school age, at which point they start sitting in chairs and modelling their habits on adults," says Richard Rosen of the Yoga Research and Education Centre in California. "In traditional cultures, where people don't sit in chairs, move around all day and squat frequently, they don't have posture problems or the aches that accompany them."

Current ergonomic thinking has it that perching - the position favoured by practitioners of the Alexander technique and martial artists - is preferable to sitting, because muscular exertion is balanced between the back and front of the spine. As for standing, correcting your posture is not as simple as throwing your shoulders back, making your spine ramrod straight and thrusting your chest forward.

Skew insists that rigidity is an enemy of good posture. "The spine is designed to be flexible and stable, and rigidity reduces flexibility," he says. "It's also designed to be symmetrical. As we age, we become increasingly left or right-handed, and therefore lose symmetry. The best thing we can do for our posture is swap our telephone from hand to hand when we use it, vary the hip we carry our children on, and work with free weights at the gym rather than machines to ensure that we work each side of our body equally."

Pat Norris, lycra-clad age-defying septuagenarian, insists that it's a matter of identifying different sections of the body as building blocks. "From the first moment we learn to stand as children," she says, "we splay our feet outward, which immediately puts our body out of line. From then on, people assume that by arching their backs and splaying their feet, they are standing correctly. This couldn't be further from the truth."

Her alignment technique involves slotting each building block into place, rotating your hips forward to fight the clenched buttock effect which pinches the nerve at the base of the spine, and pushing your shoulders down to free up your neck. "If you exercise on top of a body that is out of line, you will just build muscles on top of a shape which is wrong," she says. "That's why body-builders lose their necks."

Many factors conspire to make you slouch while standing. The naturally slopey-shouldered among us, for example, are more inclined towards bad posture because we hunch to keep our bra straps or shoulder bags in place. The paraphernalia of modern living - mobile phones, laptops, work documents - can combine to weigh upwards of two kilos. Unfortunately, the urban chic posture-friendly bumbags and backpacks which graced last season's catwalks were replaced by huge Louis Vuitton shoulder affairs during recent shows. There are fashion issues to be overcome here.

A pain-free back isn't the limit of the potential benefits of good posture. Depending on who you talk to, standing right can also get you the following: sleep if you're an insomniac, stress relief if you're tense, a flat stomach if you're pot-bellied, a few extra inches if you're short, better sex whatever , a sharp jaw line if you're multiple-chinned, and a pain-free existence if you're prone to headaches. But more toned? Thinner?

"Oh yes," says Norris, who begins her private seminars and corporate coaching sessions alike by twisting her leg slightly at the hip, and instantly and dramatically losing several inches. "I am not going to teach you how to get rid of your belly," she says. "That would be stupid. You need your belly. I am, however, going to show you where to put it." Richard Rosen agrees. "Many people in our culture think they're overweight," he says. "But when they learn how to stand with good posture, it's like they've suddenly lost five pounds."

If that isn't enough to send you screaming to your nearest Pilates class, then the psychological impact must. It's not for nothing that "standing tall" has been an analogy for self-respect in power ballads since the dawn of cheesy pop. A friend who makes heads turn and instils respect in everyone he meets simply insists: "Walk like a pop star, and people will treat you like a pop star."

&##149; Society of teachers of the Alexander technique: 0171 351 0828. Norris technique of body alignment: 0181 441 0826.