It's early morning on the banks of the river Ganges in Varanasi,

India's oldest and holiest city.

As the sun comes up and turns the pink sky gold, around 300 people are taking part in a mass yoga class.

This public yoga session for tourists was introduced two years ago by Prime Minister

Norendramodi. He calls yoga India's gift to the world. But how much do modern yoga classes really reflect

its ancient Indian traditions? I'm Mukte Jane Campion and in this BBC World Service documentary I'll be exploring the secret history of yoga.

So Virasina, the kneeling position, yoga is practiced by millions of people around the world.

You sit between your feet.

This is an Ianga class, one of the most widely practiced styles of yoga.

You may need to sit on a block.

Many of us do these days because we've got tight knees

tight hips and this is Bickram Hot Yoga where the class is put through its

postures in a studio heated to over 40 degrees Celsius.

And I'll bring your foot down one inch.

Your right foot between your palms.

Or you can also download one of the many yoga phone apps

now available to help you practice on your own.

So how did yoga come to be something that so many people are now willing to pay to learn

and put in hours to practice.

I've been attending yoga classes in London for over 20 years

and it's become an important part of my weekly routine, a time to relax, stretch and breathe.

Exhale, fatigue, tension.

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