Nairobi project trains teachers who are bringing the archer, warrior and lotus positions to young, old, rich and poor

With ambient music playing in the background, a dedicated group of yogis breathe in unison, concentrating intently on the finer details of the downward dog. Sweat drips from their faces as the teacher guides them through a series of intricate asanas, correcting stray limbs and encouraging complete focus.

But rather than a plush yoga studio with soft mats and air conditioning, the group of teenagers are working out in the concrete courtyard of a Nairobi orphanage, under the tuition of a dreadlocked instructor, Bernard Gitonga.

Until recently, yoga in Kenya was the preserve of a small group of trendy expats and south Asian devotees. But a project to encourage the practice in Africa has trained more than 80 local teachers and now offers 350 free classes a week, mostly in slum areas, serving thousands of students.

The African Yoga Project, funded by donors, volunteers and western yogis, is the brainchild of Paige Elenson, an American, who had the idea in 2007 when she was teaching yoga to Nairobi expatriates and practising with a group of young athletes in the Kibera slum. Elenson saw an opportunity to create jobs for local young people, and raised $10,000 (£6,585) to found the not-for-profit organisation and train 40 Kenyan instructors.

Billy Sadia, 29, who is from Kibera and is the group's development director, attended those first training sessions. "It was physical, it was flowing," he said. "It kind of synchronised your movements with the flow of your breath."

These days the project employs 71 teachers, who give free classes to children and adults and earn 10,000 shillings (£82) a month. They can earn up to 26,000 shillings (£197) a month offering private lessons. Gitonga, who teaches 150 students a week at the Eastleigh orphanage, said yoga allows him to support his parents and afford his own flat. For the orphans at Eastleigh, yoga is the most popular activity after football.

On the other side of Nairobi, the project is expanding into an 8,000 sq ft centre with heated studios and will train 40 more teachers this year. Francis Mburu, 25, an instructor from the Kangemi slum, said the practice was helping to break down barriers in the city. "I'm from the slum, but I go to teach in someone's mansion," he said. "They start seeing you in a different way."

Kamol Shah, a yoga teacher who is not affiliated with the project, is impressed by the diversity of students it attracts. "It's amazing to see different kinds of people coming from all areas of Nairobi for yoga," she said.

Although it will be a while before Nairobi is as yoga-mad as London – where it is said that you are never more than 50 metres from a yoga teacher – the growth of the practice does face some resistance. During the initial teacher training, Christian participants recoiled at the chanting and meditation. "To us, this was devil worship or someone trying to convert us," said Sadia.

So teachers are encouraged to avoid religious conflict by focusing on the physical rather than spiritual benefits. "What we're not is yoga missionaries," said Elenson. "We're not trying to save people through yoga."

Still, Mburu describes yoga in life-changing terms. "I used to be violent because of using drugs," he said. "What yoga did was give me a choice."

Now that he is healthy and employed, Mburu's devout Christian mother, who once feared that yoga was a cult, asked him to show her some poses. "I taught her at the house," Mburu remembers. "She was so tired afterwards."