Runners pose in front of the Cloud Gate after a warm-up run before the Chicago Marathon in 2015. Provided to China Daily

Chinese runners at this year's London Marathon included 30 from the mainland led by Tian Tongsheng, 63, one of the founders of Runnar, a company that organizes trips and assists marathoners.

"We have corporate executives, entrepreneurs, businesspeople and employees of global Fortune 500 companies, who are considered China's emerging middle class and usually hold new ideas about health," he says. "Running marathons to them has become a new normal, a new lifestyle."

Tian certainly breaks the traditional mold of aging in China, where the retirement age for men is 60. He has finished the World Marathon Majors－Tokyo, Boston, London, Berlin, Chicago and New York. Before this year's London event, he had completed 73 marathons, including 16 last year, half of which were international races.

Others have done their own analysis of Chinese marathoners.

"I see two categories: One that is rich and well educated; the other that is rich and less educated," says Oliver Qi Wang, founder and director of Runbuk, a startup registered in the United States in March that provides services to Chinese marathoners abroad.

The first group, which may have advanced academic degrees, comprises some 65 to 70 percent of runners registered with his company. Many of them live in China's biggest cities.

The second group, which makes up 30 to 35 percent, is also well-off, but many of them did not go to college, he says. They include entrepreneurs and those from smaller cities who have worked hard to pull themselves up by their bootstraps but are now concerned about their health.

Ninety percent of those who run outside China were born in the 1960s and '70s, putting them between the ages of 37 and 56, he adds. The rest are at most 10 years younger or older.

Oliver Wang, who is also CEO of Beijing-based Palace Travel and its US branch, which has runners as clients, too, describes the situation as part of a trend that started earlier in the West, in which the wealthy middle-aged started spending lots of money on fancy bicycles, for example, instead on sports cars.

Domestically, marathon fever has exploded in China. In 2014, the Chinese Athletics Association registered 51 marathon events and 900,000 runners nationwide. That mushroomed to 134 marathons and 1.5 million runners last year, according to Wang Dawei, vice-president of the CAA, which now has a marathon department. Already this year, nearly 170 marathons have been registered.