From left: The founders of Fight Republic Gym, Ryan Willis, Rory van den Berg and Jerson Estoro, along with one of their students, pose with boxing legend Manny Pacquiao. Gilbert Choy / for China Daily

The smell of sweat wafts through the air, past the print shop. Painful grunts and moans echo down the tight corridors of downtown Beijing's Shangdu Soho building.

Welcome to Beijing's fight club, the tiny gym that is Fight Republic.

The studio houses a small boxing ring with ropes, a kitchen area with drinks, and men's and women's showers. And that's all.

Professional fighters Rory van den Berg, Jerson Estoro and Ryan Willis opened Fight Republic to help people get into shape and promote Muay Thai in China.

"I've been back in the UK, and one of my friends who runs one of the biggest gyms in the UK has a big boot camp program, which is like a martial arts boot camp that he runs for six weeks," he says.

"When I came back to China, I thought it would really work here and that there was a gap in the market for it."

Van den Berg, an asset manager in Beijing, reached out to his friend and trainer Willis, who brought Estoro into the mix.

The establishment's gear is some boxing equipment and free weights. But trainers sculpt clients without fancy facilities.

Willis, who has trained in Muay Thai since he was a young child in the Philippines, teaches one-on-one sessions and children's classes.

"I was the shortest at school, and my coach saw that I had potential," he recalls.

"So I trained to be a fighter."

Willis has worked with various gyms and fighters, including Van den Berg, since coming to Beijing in 2010.