BEIJING, Dec. 9 -- Shu Hua gets up at 5 a.m. to prepare for his daily run in the Beijing Olympic Park.

Runners like him can be seen from dawn till dark, their reflective gear flickering along the road.

Running aficionado Shu is in his forties and a senior executive in a Beijing security firm. He insists on running 20 kilometers every day and does strength training three times a week.

Shu completed the Shanghai half marathon Dec.1 when the air quality index (AQI) topped 300 in some parts of the city. Over 300 means "serious" pollution.

Undaunted, more than 35,000 runners took part in the race, feeling that the immediate, concrete benefits of running far outweigh the abstract and undefined risk.

"If I checked the pollution index every day, there would be very few days that I would run," says Shu, who nevertheless uses a mobile phone app to check the index, a habit shared by many.

Xiaoxiao, 26, a web editor in central China's Hubei Province is in training for a marathon in Singapore and possible respiratory problems later in life are something she doesn't seem worried about.

"I am concerned about air quality, and I have the app for PM 2.5 on my phone, but the air won't get better just because I don't go running. Running makes me feel better and happier," says Xiao, who has trained hard for a marathon in the coastal city of Xiamen.

"I chose running because it is simple. Anyone who is able to put his right foot before his left, or vice versa, can become a runner," says Xiao.

Thousands upon thousands of people like Shu and Xiao are running marathons. There are 33 marathons annually in China and more than half a million people take part.

The Shanghai International Marathon had all 15,000 places filled in four hours and the official website crashed due to excess traffic.

More than 70,000 runners have registered for the Xiamen International Marathon on Jan. 4, 2014, Shu Hua among them.

"For us, every marathon in every city is a feel-good dopamine festival of arrival, running, celebration and return to Beijing."

Shu hopes to complete all marathons held in China, then meet challenges from international games like UTMF (Ultra Trail Mount Fuji), UVU North Pole Marathon and the Escape from Alcatraz Triathlon Series.

"To hear my feet thud against the treadmill is music to my ears, and the drops of perspiration shed are tears of fat crying for its demise," Shu said when asked about his infatuation with running.

Shu reckons lazy people use the smog as an excuse for not running or doing any outdoor sports, but they can still run indoors on treadmills. At this time of year treadmills and leg press machines are very much in demand at gyms.

"We have had more members at our gym in the last few months because more and more people want to get into shape. The air is fresh in here because we recently had big filters installed," said Linda Hong, who works at a Shanghai gym.

Shu said his idol is US runner Joy Johnson, who once said that "I want to keep running as long as I can and drop dead in running shoes when the time comes."

That's exactly what she did at the age of 86, one day after this year's New York marathon.