There are many ways to stretch a muscle and iron out the knots of everyday life. You can do it on a yoga mat, flexing your spirit as you go. You can lengthen your limbs with precision in Pilates. Or, in the latest approach to this element of fitness, you can have your hamstrings pushed to the point of mild discomfort and beyond by a therapist intent on exploring the limits of your body's bendiness. At the UK's first dedicated flexibility centre, Stretch, which opens in London next week, do not expect soft lighting or scented candles. Here, the setting is clinical (its base is a medical centre off Harley Street) and the techniques more forceful than those typically practised in mind-body studios.

Using a method called Active Isolated Stretching (AIS), its "stretch therapists" promise to "realign your posture, boost your energy, improve your flexibility and even make you feel younger". So far, so much like yoga, you may think. Yet the key difference is that you flex a single muscle at a time. "We put the body into the correct position to isolate just one muscle and then help someone to hold that stretch for around two seconds," explains therapist Courtney Radcliff. "If you stretch for longer, the body's protective reflex kicks in and causes your muscle to contract." Each stretch is repeated eight to 10 times in a "pumping action", which serves "to boost circulation, fill your muscles with energising oxygen and flush out waste products".

In America and Hong Kong, clinics from the Stretch chain already have a huge and dedicated clientele, ranging from those looking to prevent or treat alignment problems to people who want to enhance their sports or gym performance. The fitness industry has placed such emphasis on the benefits of stretching that few imagine we can do without it. Sedentary lifestyles mean our range of movement is restricted and the resultant lack of flexibility is responsible for an increase in back, neck and postural imbalances. Yet, as the popularity of stretching has risen, so has the number of scientific experts questioning its merits.

Some suggest even general stretching is unnecessary and that a poor technique can do more harm than good. "Most normally active individuals only need to maintain normal range of motion to function at a high level and to function safely," says Cedric Bryant, chief exercise physiologist at the American Council on Exercise. Too many people, however, don't stop there. "They think that if being able to touch your toes is considered normal, then being able to touch four inches past your toes must be better," Bryant says. "There is evidence to suggest that hypermobility in some people can be a risk factor for injury."

Professor William Roberts of the University of Minnesota, a former president of the American College of Sports Medicine, agrees: "Sitting at your desk in good posture will do more to decrease your risk of repetitive injury." While Dr John Buckley, a physiologist at Keele University and a spokesperson for the British Association of Sport and Exercise Sciences, says: "There is a belief that stretching will improve performance or prevent injury. Unfortunately, the evidence on this front is debatable. In fact, poor stretching can lead to decreased muscle function."

Indeed, last year, Dr Ian Shrier of the centre for epidemiology at the Jewish General Hospital in Montreal, a past president of the Canadian Academy of Sport Medicine, reviewed the evidence for the Physician and Sports medicine journal. He concluded that when performed immediately prior to a workout, stretching causes a small, albeit temporary, reduction in a muscle's power and force. For anyone needing to perform kicks or jumps (in football or martial arts) or who wants to lift weights, this could be limiting.

In spite of this glut of negative evidence, experts are keen to stress that stretching can still play a role in good health. That role is just more limited than once thought. Buckley says: "Regular teasing of the joints as a result of stretching may lead to improved joint position feedback mechanisms, otherwise known as muscle proprioception, which are essential for good balance and coordination."

Ultimately, however, the goal of stretching should be to counteract normal stiffness and ensure full range of motion, making day-to-day activities easier. Light stretching most days is "enough to maintain and/or improve muscle and joint mobility," Buckley says. "And the best time to stretch is at the end of a training session or at the end of the day when the muscles are warm and the joints well lubricated."

· Stretch opens at the Queen Anne Medical Centre, 18-22 Queen Anne Street, London W1G 8HU on April 18 (020-7034 3340 or www.stretch.co.uk).