Bent out of shape London - Arabstoday Downward dog for back pain, sun salutations for an energy boost - yoga has become the workout for a healthy mind and body, and is the exercise of choice for endless celebrities including Brad Pitt and Jennifer Aniston. But is the ancient art form as healthy as we’d like to think? On yesterday’s Today programme on Radio 4, New York Times science writer William Broad, the author of a controversial new book, The Science Of Yoga: The Risks And Rewards, asked whether yoga - when taught incorrectly - might actually have the potential to kill. During his research Broad - who himself practised yoga for many years before getting injured doing it in 2007 - uncovered endless documented examples of injuries to backs and limbs such as strains, broken bones and trapped sciatic nerves. He also found to his ‘horror’ that while some poses were low risk others could have extremely serious consequences. These risks, he says, occur as a result of hyper-extension - over-stretching - of the head and neck. It’s not just doing advanced postures such as headstands, where you balance your legs straight up in the air, resting on just your head and hands, that are risky, says Broad. He’s gathered evidence that even traditional yoga moves, or asanas, practised at beginner and intermediate level, can lead to serious problems. ‘This is not anecdotal and they are not freak accidents,’ he says. ‘Postures like the shoulder stand, in which you lie on your back and raise your legs into the air, and the plough, in which you lie on your back and put your feet over your head on the floor behind you, that are widely performed can crank the neck around in a risky way.’ Reductions of blood flow in one of the vertebral arteries, called the basilar artery, are known to cause strokes in some people and can be fatal. ‘If the clots that form go to the brain, you can have a stroke,’ Broad says. ‘And one in 20 people who have these vertebral artery problems can die.’ He explains that the first real evidence of yoga injuries was initially published in credible medical journals several decades ago. As long ago as 1972, a respected Oxford University neurologist, Professor Ritchie Russell, wrote an article in the British Medical Journal arguing that some yoga postures had the potential to cause strokes in healthy, young people. He had found evidence that yoga students typically turned their necks as far as 90 degrees, double what is considered a normal, healthy rotation. Such excessive extension of the head and neck, Russell said, could harm the fragile arteries running along the neck, causing clots, swelling and constriction. In theory, he said this could produce serious problems in the brain. In 1973, a spinal rehabilitation expert at Cornell University Medical College described the case of a 28-year-old woman who suffered a stroke while doing a yoga move known as the wheel or upward bow in which a person lies on their back and then lifts their body into an arc, balancing on the hands and feet in a sort of back-bend. Instead of allowing the head to hang in this position, many people tense and move their necks in an attempt to create balance, a move which can dangerously backfire. A few years later another paper, this time in the Archives of Neurology Journal, detailed the case of a 25-year-old man who was rushed to hospital with loss of control in the left side of his body and blurred vision. Again, yoga was to blame. The patient had been performing daily asanas every morning, including spinal twists in which participants lie or sit on the floor and twist their upper body in the opposite direction to their lower body to stretch the spine, as well as shoulder stands, often maintaining the positions for five minutes. 'One man suffered a stroke after his artery was blocked'Doctors wrote that a series of bruises down his lower neck were a result of trauma ‘caused by repeated contact with the hard floor surface on which he did his yoga exercises’. Examinations revealed he had suffered a stroke after his left vertebral artery became blocked, preventing blood from reaching his brain. While he recovered the ability to walk, his hand function remained damaged. Over the years, Broad says that there is an increasing amount of ‘real data that medical and government communications have gathered’ confirming yoga’s risks. In 2001, the prestigious New England Journal of Medicine published an article citing yoga as one of the many possible causes for arterial damage in susceptible patients. Broad also cites a 2009 survey of US yoga therapists, teachers and doctors that looked at the most common yoga-related injuries. The researchers from Columbia University found that while back injuries were, predictably, the most usual, the next most common in declining order of prevalence were shoulder injuries, knee problems, neck injuries and then strokes. ‘The respondents noted four cases in which yoga’s extreme bending and contortions resulted in some degree of brain damage,’ Broad writes. ‘The numbers weren’t alarming, but the acknowledgement of risk pointed to a decided shift in the perception of the dangers yoga posed.’ So common are yoga-related injuries that they are even being recognised in medical dictionaries. Broad highlights the case of a young man who was relatively experienced at yoga and spent several hours a day in a kneeling position known as vajrasana - something that is not advised for long lengths of time. After a few weeks, he had difficulty walking or climbing stairs and went to see his doctor for an explanation. He was told that the kneeling posture had prevented oxygen from reaching a branch of the sciatic nerve that runs from the lower spine through the buttocks and legs. As a result, the nerve had become temporarily deadened and, after seeing several other cases of the same injury, doctors named the condition ‘yoga foot drop’. Glenn Black, a yoga teacher for nearly 40 years, who spoke to Broad when he was doing his research, says he has seen everything from pinched nerves, lower back tightness and injuries to hips and knees - and worse - among yoga regulars. He says moves such as the chaturanga - a challenging pose similar to the plank in which all four limbs and the core abdominal muscles support the body - can create repetitive use injuries in the shoulder. He adds that moves with deep knee flexion such as deep squats, which are a feature of many standard yoga postures, can strain ligaments and tendons. 'Yoga's not bad for you but bad teaching is'Lifting the head - instead of letting it hang - during arm balances, in which you support the entire body with the hands on the floor, can also restrict blood flow to the brain and around the body, Black says. Any asanas involving flexing, extending and rotating the lower back and cervical spine can cause problems. ‘It’s a myth that it’s safe to do an asana without awareness and consciousness,’ Black says. Indeed he has come to believe that ‘the vast majority of people’ should give up yoga altogether. Furthermore, he is convinced that people are ending up in hospital because they have underlying physical problems that make serious injury more likely. Instead of doing yoga, they should be doing specific exercises to strengthen these weaker parts of their bodies. But is Broad being alarmist? In the UK, the growth in the number of people taking part in yoga - it is now thought to be close to one million - has predictably led to a growth in related injuries, according to  the Society of Sports Therapists, but there are no reported cases of anyone suffering a stroke as a result of yoga exercises. Defenders claim its links to injury and pain can mostly be caused by  poor teaching. Yoga is woefully unregulated in the UK and anyone can become an instructor after completing a weekend course. Pierre Bibby, chief executive of the British Wheel of Yoga, the national governing body says: ‘Yoga is not bad for you, but bad teaching is.’ The BWA’s own instructors undergo a minimum of two to four years’ tuition. Others blame the fact that yoga has become too competitive. ‘People push themselves too far,’ says Mollie McClelland, a yoga teacher at the Alchemy Centre in London.  ‘And there are such huge egos in yoga that everyone wants to prove a point.’ Broad agrees that yoga does have benefits. It can relieve stress and decrease pain, but it can be a disappointment for those expecting it to bring miraculous changes to body and mind. It was while doing the extended-side-angle pose, a posture hailed as a cure for many diseases, that Broad’s own back ‘gave way’ five years ago. ‘With it,’ he says, ‘went my belief, naïve in retrospect, that yoga was a source of only healing, never harm.’ MailOnline .