25 September 2013 Last updated at 20:16 ET By Tim Mansel BBC News

Very little research has been done into the value of yoga and meditation in prisons - but many prisoners have found they help overcome the stresses and strains of life behind bars. Prison authorities too are waking up to the possible benefits, providing classes in the hope of fostering a calm and positive atmosphere.

The precision of the poses is remarkable - and for Nick, a man in his early 40s, apparently effortless.

We're in a small yoga studio above a pub in west London, daylight filtering in through slatted blinds. Nick holds Warrior 2 - arms stretched horizontally, one knee bent, one straight behind him Then he offers to demonstrate a handstand, and lifts himself on the palms of his hands, knees and feet together.

He is a model of balance and control.

"That's six years in prison," he grins.

Prison was Villa Devoto, in Buenos Aires, Argentina.

"It was the worst place I had seen in my life," Nick says. "They don't have cells, they have open wings, where you can have anything from 100 to 400 people per wing. There were no beds so you'd literally be like sardines sleeping on the floor."

He demonstrates this, lying on his side on his yoga mat, his head propped on his hand.

Nick was no innocent. Together with a friend, he'd run a highly successful business smuggling cocaine supplied from Colombia to Europe. They were multi-millionaires.

Link:
How yoga is helping prisoners stay calm