China's tennis boom over the last decade has primarily been a big-city phenomenon. However, American coach Joshua Robinson is showing that the sport's growth needn't be confined to urban areas.

Every afternoon after school, children flock to a tennis court in Qinghai province's rural county of Huzhu to attend Robinson's classes.

Thirty-seven years old and rarely seen in anything other than sportswear, Robinson hails from Wisconsin, USA, and graduated from the University of Milwaukee, where he studied Chinese, in 2013.

A passionate sportsman, he began playing tennis at the age of 12, and also enjoys baseball, rugby and swimming.

Influenced by his mother, Robinson became fascinated by China. The American first arrived in the country in 2009 to study Chinese in Inner Mongolia's capital Hohhot, and also worked as a private tennis coach in Beijing.

Judging from the fluency of his Chinese, it's hard to believe he isn't a native speaker.

"In the autumn of 2013, I came to Qinghai province for the first time," he said. "The blue sky, white clouds and snow mountains impressed me. What surprised me even more was that a remote county such as Huzhu had clay courts just like at the French Open."

Afterwards, Robinson returned to Beijing where he continued working as a tennis coach. The job was easy and well paid, but ultimately he felt unfulfilled.

"I wanted to teach more children to play tennis, but there's no shortage of good coaches in a big city like Beijing. I wanted to go to a place where I could make a difference," he said.

In 2017, Robinson came to Huzhu, renting local tennis courts and beginning his new career. However, things did not initially go to plan.

"Tennis is no longer a new sport for children in big cities, but children here are still unfamiliar with it. I went round schools and handed out leaflets, but only two children enrolled," he said.

Although frustrated by the lack of interest, he remained devoted to coaching and also taught English.

Soon, news spread that a foreign coach had come to the remote county and, by the spring of 2018, Robinson had nearly 20 students attending classes. Many parents, however, had enrolled their children primarily so they could learn English.

"Teaching both English and tennis attracted more parents and children, but I just wanted to focus on tennis coaching. Eventually I decided not to teach English anymore, and many children gave up," he said.

At present, Robinson teaches both junior and senior classes, with his students raging in age from 4 to 13. At weekends, he often takes students to compete in events in large cities like Xi'an, Lanzhou and Chengdu.

Robinson also holds winter and summer training camps in Huzhu, which attract children from as far afield as Chongqing, Beijing, Hunan and Guangdong.

But even within Robinson's Qinghai classes there is great diversity, with children from Tu, Tibetan and Korean ethnic minorities on the court, something that fascinates the Wisconsin native.

"Many people living around me still do farm work at home. During the busy season, some of my coaches have to go home, digging potatoes to help their families," said Robinson, adding that he hopes more local coaches can be trained to boost the sport's development in remote areas.

"Learning tennis not only improves children's fitness, but also teaches them to overcome stress and challenges from an early age. I hope tennis can give some of them a better life."