The dense smog lingering over Beijing has affected outdoor exercises in the capital, and experts have suggested avoiding fitness activities even at indoor gyms.

"In most fitness centers, the circulation system links the air inside with the outside environment. So the air quality in most gyms is actually not as good as people think, especially during smoggy periods," said Zhou Qinlu, a fitness expert with the Beijing Municipal Institute of Sports Science.

"If people really want to work out, they should do some slow-motion exercises like yoga or tai chi at indoor venues equipped with air filters."