A $5bn industry is outraged over a New York Times article saying that the keep fit regime is bad for your body

One of the most common sights in New York is slim, young professional women scurrying across the city with rolled-up yoga mats under their arms and determined looks, cramming in a dawn or lunchtime session between power moves in the office. So perhaps it should come as no surprise that an incendiary magazine piece in the New York Times, under the headline, "How yoga can wreck your body", has turned the usually chilled community of yoga-lovers upside down. In the US, and perhaps even in Britain, where an estimated million people practise regularly, yoga may never be the same again.

The offending article, which appeared across several pages of the paper's prestigious Sunday magazine, was written by senior science writer William Broad. In it, he alleged that students and even "celebrated teachers" were injuring themselves "in droves" by over-ambitious and under-taught yoga moves.

He also quoted at length the views of local yoga veteran Glenn Black, who seriously hurt his back after years of practice. According to Black, "the vast majority of people should give up yoga altogether" because it's too likely to cause them serious damage.

The result has been acrimony, recrimination and a ferocious backlash from representatives of a $5bn-plus industry in America with an estimated 20 million followers – five times more than 10 years ago. Drivel, sensationalism, disgraceful hype, bizarre and misleading were just some of the criticisms posted online and expressed to the Observer. After more than 700 comments had been posted on the New York Times website, there was no room for more.

The well-known Ashtanga New York group retaliated with an article on its own website entitled "How the New York Times can wreck yoga".

Meanwhile, the controversy quickly became the talk of the hundreds of studios all over the city and the hundreds of thousands beyond.

"I'm shocked. Yoga transformed my life and I love going to practise – it's made me healthier and much calmer and my body feels more alive," said Susan Davies, 28, a software designer, as she walked near Central Park on the way to her twice-weekly class. "I'm more balanced and yet more assertive and efficient at work – my friends who do yoga say the same."

Paula Tulsi, who runs the Manhattan practice Reflections Yoga, said: "The controversy is massive. People in the circles I run in are going crazy, because lots of people who were going to try yoga – the people you can bring in and heal – are going to be afraid now and they'll think yoga's bad. That's so tragic and angering."

"I thought it was insulting to the yoga community," said massage therapist Eddie Rodriguez, who runs the Maio Physical Therapy practice in New York. But Rodriguez did point out that many yoga classes are too crowded and most people aren't aware that many instructors are barely trained – even though they may look the part. "I encourage my clients to try yoga. But get a recommendation by word of mouth, don't just go to a studio because it's got a free offer, it's on the gym schedule or it's nearby and has classes at convenient times. It's definitely a case of buyer beware," he said.

And in New York, at least, tales of yoga disasters are not difficult to find. Arts administrator Elizabeth Bennett, 45, slipped a disc in her neck after being "bullied" into a headstand at a New York yoga studio. "When I hesitated, he called me a wimp. There are too many teachers who push unwitting students too far to serve their own egos," she said.

Despite having health insurance, she ended up spending about $8,000 of her own money on acupuncture and months of physiotherapy until she was pain-free again. Bennett added that people trust yoga and rely on it as a source of healing, not injury, but are now learning to be a lot more sceptical and discerning in their choice of studio.

Anatomy experts also warn – as did Broad's article – about the risks of inverted poses, which can strain cervical vertebrae or restrict blood flow into the head, either acutely or progressively.

David Patane sees up to 10 clients a year with a current or past yoga injury at his Physique corrective exercise, movement and lifestyle coaching business in Manhattan. He said the computer age has given so many people slouched postures and expanded waistlines that they are inviting injury if they jump up from their chairs and unthinkingly start twisting themselves, on demand, into poses that hyper-extend the often already weakened neck and lumbar spine.

"A neck pushed forward one inch in front of the plumb line of correct alignment – common with slumped posture – is already putting seven pounds of stress on the cervical spinal column," he said. When these people flipped into a shoulder stand, or bent their legs back over their heads in "plough pose", there was a greater risk of injury, he said.

Megan Branch, 22, an executive assistant at a web company, strained her back last year simply by doing the "superman'", where you lie on your front and raise your legs and arms simultaneously, because she was in a class that was so crowded with up to 70 people that she had to lie at an odd angle so the next student did not have his feet in her face.

"I felt something snap in my back and then I went limp," she said. She recovered by resting and stretching carefully, but her back now feels less stable.

The $5 community class, like many, simply had a leader to mimic, with no expert correction of students' postures or warnings about injuries or not pushing one's limits. In an industry where there is cursory certification and no official licensing, yoga teachers can become "qualified" with a 200-hour online course.

"Many teachers are coming out of training and don't even know the three different hamstring muscles," said Emilia Conradson, who branched out from teaching the Forrest school of yoga into her own therapy business Body In Balance in New York, which also treats yoga injuries. "Their understanding of anatomy is laughable, and yet yoga is about the physical as well as the spiritual and needs to be safe." Other experts blame the "westernisation" of yoga as more of a workout than a holistic practice.

Even Tulsi, while furious at the inflammatory nature of Broad's attack, does admit that the debate is timely. "It's not yoga, it's the bad translation or teaching of yoga that's the problem," she said.

After a row that threatened to throw one of America's favourite middle-class leisure pursuits off balance the lesson for devotees is clear: take care and take your time when choosing your next yoga class.