Mumil. You may not know the name - because I just invented it - but you know her. She's the middle-aged mum in Lycra. She's at the school gate in leggings, an 18-piece bra top and neon-laced trainers. Yoga bag in hand, she'll be doing "discreet" stretches as you wait for the bell to go.Since it first arrived in the West, courtesy of Swami Vivekananda, yoga has been subject to all of our best commercialising and self-indulgent instincts. Celebrities got hold of it pretty quickly: by the early 1930s, Charlie Chaplin, Greta Garbo and Aldous Huxley were firm friends with Indian philosopher Jiddu Krishnamurti, and Hollywood's first yoga studio, set up in 1947, counted Gloria Swanson among its regulars.Yoga teacher Richard Hittleman first brought it to the American masses via television in 1961, while Maharishi Mahesh Yogi's association with the Beatles in the late 1960s gave the practice further impetus. The fitness craze of the 1980s and the rise of environmental concerns in the 1990s fuelled its popularity.It's hard not to argue that since then yoga has become a form of retail rather than spiritual therapy. There are now more than half a million practitioners in the UK alone, 83% of them women.A friend of mine calls her local Mumils "spiritual spiralisers", arguing that, just as we are turning courgettes into pretend spaghetti, so Western women are making yoga palatable by removing its essence.It is partly, perhaps, to try to arrest this increasing tendency to bury yoga's ancient and anti-individualistic origins under a deluge of branded stretch pants that the UN recently ceded to India's request to mark International Yoga Day, as a way of reminding us of its roots.Earlier this month, people gathered to perform asanas and mass-align chakras in 251 cities in 192 countries, with a particular gathering on London's South Bank that included me.The hour under ashtanga specialist Jane Sleven passed quickly and painlessly. It is the only physical exercise I have ever enjoyed. Afterwards, I asked Jane if she was bothered by the deluge of yummy Mumils at studios, ashrams and luxury retreats. "No, it doesn't matter. I'm delighted to see it become so widespread," she said."Look at me. I went through a period of worrying that I'm a little bit plump, a little bit stocky, I'm closing in - very fast - on 70, and I nearly stopped teaching. But then I thought, no! I'm going to be little, old, plump Jane who can demonstrate to other people who aren't 'golden' that yoga is amazing and can give you, like it has me, an amazing life." ..