Yoga practitioners often tout the unique health benefits of the ancient discipline—from relieving stress and pain to improving vascular health—but most doctors remain sceptical in the absence of hard proof.
The International Journal of Yoga Therapy (IJYT) published last year highlighted dozens of studies purporting to show that the practice can help people with eating disorders, soon-to-be moms and women with cancer-related symptoms.
Lionel Coudron, a 60-year-old French doctor, claims he is pain-free thanks to three hours of yoga per week.
"A few years ago, people thought yoga was (essentially) good at combatting stress", said the doctor, who set up a yoga therapy institute in Paris in 1993.
But the benefits of yoga—including meditation, breathing exercises and posture—go much deeper, Coudron said.
Jocelyne Borel-Kuhner, former head of an emergency ward in a Paris hospital, agrees.
She set up the very first yoga therapy practice in 2012 with the specific aim of relieving pain for patients, particularly those with handicaps or arthritis.
Yoga therapy "isn't just a course of yoga adapted for people who are ill," but is individual consultation with a clinical examination followed by a care plan using yoga techniques.
The aim is to limit the therapy to between three and five consultations per patient, followed by exercises to be continued at home afterwards.
Six years and more than 2,000 consultations later, more than 800 patients have passed through Borel-Kuhner's practice, with some deciding to cease traditional treatment altogether because the yoga therapy is so successful.
Nevertheless, even proponents acknowledge there is little consensus on what might constitute specifically therapeutic stretches and poses.
"The lack of standardisation of yoga practices, and the fact that many yoga tools have filtered out into the broader world, begs the important question of what constitutes yoga therapy," two practitioners, Matthew Taylor and Timothy McCall, wrote in their lead essay for the IJYT.
A study released in January, for example, found no distinct health benefits between traditional yoga and Bikram, carried out in hot and humid rooms.
However, Taylor told AFP that hasn't dampened his enthusiasm.
"The scepticism is vanishing quite quickly and enthusiasm is now more the response, especially in light of the worldwide epidemic of chronic pain," he said.
Most studies which have been carried out, however, including peer-reviewed findings in journals like The Lancet or JAMA, have failed to pass muster with doctors and scientists.
While they point to research showing that yoga can indeed improve health, nothing appears to suggest such benefits could not be had through walking, swimming or other exercises and sports.
"There is evidence that doing yoga has specific health benefits. However, those benefits are likely not specific to yoga and are universal to exercise," the American doctor Steven Novella wrote last October on the website Science-based Medicine.
And Novella added that "all of the mystical and pseudo-scientific (trappings) that often accompanies yoga is counterproductive".
Yoga: Indian practice turned global phenomenon
The Indian discipline of yoga, involving spiritual and physical practices, is followed in myriad forms today by millions of people worldwide, with an entry in UNESCO's intangible cultural heritage list.
Here is some background:
The word "yoga" has its origins in the ancient Sanskrit language and means "to attach, join, harness, yoke".
This is the notion underpinning the discipline, according to French historian Bernard Sergent, which is to join the intellect of the one practising with the "universal soul".
Yoga first appeared in ancient texts such as the sacred Hindu epic the Bhagavad Gita, written between the fifth and second centuries BC.
It is born of an "awareness of the unsatisfactory character of the human condition," says India specialist Tara Michael, author of the book "Yoga" published in France in 1980.
The practice emerged as a way of transcending this suffering.
However in its present-day use, yoga is often no more than a form of exercise, Michael says.
A modern (re)invention
Yoga became known in the West towards the end of the 19th century as it was undergoing a major revival in India under the Hindu teacher Swami Vivekananda (1863-1902).
This philosopher-monk stressed yoga's rational and scientific qualities in a bid to make the discipline compatible with the West.
His book "Raja Yoga" lays the foundations for a modern and international yoga.
In the first half of the 20th century, Western texts began to detail yoga postures, also known as "asanas".
The emphasis on these postures and their sequences, such as the famous Sun Salutations, is a recent development, says India specialist Sita Reddy in "Yoga, The Art of Transformation" (2013).
Modern Western references such as the Oxford English Dictionary define yoga as a "spiritual and ascetic discipline" which includes "breath control, simple meditation, and the adoption of specific bodily postures."
Today there are many techniques popular around the world, including the classic Hatha; Ashtanga's series of sequences; Iyengar, which uses props; and Bikram, practised in a heated and humid room.
Indian metaphysics captured the imagination of counter-cultural movements of the 1960s and 1970s, as epitomised by the relationship between The Beatles and the Indian guru Maharishi Mahesh.
Yoga as a spiritual practice was popularised at this time with the more athletic and dynamic methods developed in the 1980s and 1990s, says Mark Singleton from the School of Oriental and African Studies in London.
It is difficult to say just how many people practise yoga around the world today, although some estimate it could be up to around 200 to 300 million.
Studies have shown its benefits for dealing with anxiety, depression and sleep disorders, with yoga considered more effective than a simple physical activity but less than psychotherapy.
Since coming to power in 2014, India's Prime Minister Narendra Modi has taken yoga as an emblem of India's flourishing in the world, pushing for the UN resolution that has since 2015 consecrated June 21 as International Yoga Day.
UNESCO added yoga to its list of intangible cultural heritage in 2016 in recognition of its influence on Indian society, "from health and medicine to education and the arts".
"Designed to help individuals build self-realisation, ease any suffering they may be experiencing and allow for a state of liberation, (yoga) is practised by the young and old without discriminating against gender, class or religion," UNESCO added in a tweet.
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