In normal times the rising sun's rays that bounce off skyscrapers in downtown Beijing are something that thousands of retirees can enjoy each morning as they stroll through the Temple of Heaven Park five kilometers away.

But that was before COVID-19 cast its pall over Beijing, and in recent weeks the numbers of folk taking that early morning stroll have become vastly depleted.

But for someone like Guan Jingxue, keen on using such parks for something a lot more serious than a morning stroll, there can be no letting up. Guan, 71, lean and tough, of medium height, and with no discernible trace of fat on his belly, is a native of Benxi, Liaoning province, who used to work in a textile factory.

In 1996 he came down with a stomach illness, and with the aim of strengthening his immune system he started running in a playground near the factory.

At the time, few people in China were regular joggers, and fewer still ran in groups. It was then that Guan spotted members of a running group training in the playground, and he eventually joined them. At the time he was in his mid-40s and it was only after six months that it ceased being a struggle for him to keep up with them, and a little longer before he felt quite comfortable with the rhythm and pace of their training.

A little later he felt confident enough to formally join the group and become very serious about what he was doing.

"I guess I've got a bit of talent,"Guan says.

After a little more than a year of training he could produce some empirical evidence for that modest self-assessment as well as his determination: he could run 10 kilometers in a very respectable time of 36 or 37 minutes.

Brimming with self-confidence, he pressed on to improve his performances and says that very rarely over 24 years has he slacked off in his training regime, competing in the Beijing Marathon in 2004 and in every year since 2006 until last year.

He began to compete in other marathons, too, his performance in the Xiamen Marathon in 2012 being particularly notable, with a finishing time of 2:56:42, by which point he had become one of the most outstanding marathon runners in his age group in the country.

Three years earlier he had retired and soon after, family duties beckoned. He was needed in Beijing to take care of his granddaughter, and with great trepidation, and bringing with him almost a lifetime of memories from the relatively small city of Benxi, moved to bustling Beijing at the age of 60. One of his main concerns was about having to adapt to a totally different environment so late in life.

However, one beauty of running is that it is both a very transportable skill akin to an international language, and before long Guan could say he was truly in his element, thanks to Yuandadu Marathon Club.

"In the club, runners are divided into six levels of A, B, C, D, E and F,"Guan says.

"I'm in group C, those who can finish the full course in a time of anything between 3 hours and 3 hours and 20 minutes. We can work together and get a better result with a similar training rhythm. During the COVID-19 epidemic we have been encouraging each other to keep up the work, and to this end I've been doing spinning training at home."

Being an elite runner, Guan used to do at least five exercise sessions a week, and he would run at least 200 kilometers a month. Training with others is particularly helpful in improving performance, he says, as is a focused attitude toward running. He spends little on equipment, and unlike many top runners is not preoccupied with his diet.

In 2017 he competed in the Boston Marathon and finished ninth in the 65-69 age group. For him his performance was below par, and it made him realize that he had a lot of scope for improvement.

"There were 652 people in my age group, which is unimaginable in China."

In the 2019 Beijing Marathon in November, Guan finished second among those over 65, with a time of 03:01:55. Again he was dissatisfied, because he has set himself the goal of running under 3 hours before he is 73.

As he gets older, his physical fitness has declined, but Guan has developed a more rigorous training plan so he can realize his 3-hour dream. Every morning he runs for 1 hour in Wanghe Park, near his home; he takes part in Yuandadu's systematic running training; and he goes to Olympic Forest Park in the city's north every Sunday to run 25 to 30 kilometers as long-distance training.

He had planned to compete in the Boston Marathon again this year, but the race, which was supposed to have taken place on April 20, was put back to Sept 14 because of COVID-19, the first time the race has been postponed in its 123-year history.

Guan was to have run in the 70-74 age group.

"I had looked at things carefully, and there's an American who can do 2 hours and 58 minutes, and I had wanted to finish in the top three."

With the construction of urban and rural public sports and exercise facilities accelerated, and the national fitness program taking root, there seems to be no end in sight for the increasing popularity of the marathon.

"It's become really fashionable,"Guan says. "These days you get 100,000 people competing for 30,000 spots in the Beijing Marathon, and the number of senior runners is increasing. At the National Veterans Championship I took part in last year there were even centenarians in the 100-meter race."

Of Yuandadu Marathon Club's 600 members, 65 are aged between 50 to 60, and five are older than 60.Seven of those aged over 50 have a personal best time under 3 hours, 17 have a best time of between 3 hours and 3 hours and 20 minutes, and the rest can finish a marathon in between 3 hours and 30 minute and 4 hours, the club spokeswoman Wu Ping says.

As for Guan, that granddaughter he moved to Beijing to look after all those years ago is now a teenager, and his daily activities in addition to running include playing with her and making sure she gets to school safely.

As he has watched her grow there is little doubt that he will have impressed on her the importance of determination and resilience.

"Life is a process of constantly challenging yourself and breaking through your own barriers again and again," he says.

"I'll be running until the day I can't move."