Zhang practices slacklining in the space under high overpasses in Shanghai. [Photo by Zhang Zefeng and Zhao Zhongjun/China Daily]

Zhang calls the sport "moving meditation".

"While walking, one needs to spend most of the time concentrating, taking slow breaths and adjusting the body," he says.

When Nanjing-based engineer Yang Lianwu faced difficulties with the 100-meter-long slackline, Zhang advised him to clear his mind and take one step at a time.

"One of the most effective ways to achieve a goal is taking every single step well," says Yang. "Then success knocks on your door without you realizing it."

Yang has tried various extreme sports, including rock climbing, parkour and BMX bike racing, but he sees slacklining as the most rewarding.

He says unlike other sports, which require team spirit, slackliners mostly walk alone. "When you are facing yourself alone, you are more likely to find inner strength."