Alexander Woo, 79, began running in the New York City Marathon with his inspiration being to get to see his grandson grow up.

On Sunday, Woo completed his second New York marathon, in five hours and 51 minutes. Wu said he started running when his grandson was born five years ago so that he could live long enough to see him go to high school, college and even further. Woo previously ran in the marathon in 2010.

Woo arrived in the United States in the 1960s from Hong Kong, where he was working as an immigration officer for the colonial government.

Not content with staying in "the cubicle of my office, I wanted to see the world," he said.

Upon arriving in the states, Woo worked as a dishwasher. He earned a business degree in the 1970s in night school and started his own jewelry business in the 1980s. He also has visited dozens of countries.

For Woo, "running is a metaphor for accomplishment," said his daughter, Alex Woo. "He has accomplished a lot and doesn't need to prove himself anymore. Marathon is a new challenge to him."

Woo admitted that running was "very painful" at the beginning. "But if you set your mind to it, you will do it," he said.

Every time he wanted to give up, the image of his grandson and Alex came to mind and then he "started to have more energy," he said. At first, he used to rest after 10 minutes of running, but now he runs 10 miles nonstop every night.

Sunday's marathon attracted more than 50,000 runners - 38 percent of those international participants. Forty-six Chinese citizens participated, according to a marathon spokesperson.

"Running is open to everyone, with no barricade to anyone," said Yu Jia, a noted sports commentator in China and head of +U Running, a Beijing-based running community.

"It is joy for the body and training for the soul," he said. "You beat difficulties again and again, and you become more and more confident. Even though some runners don't have a very good record in terms of time, people around them can still be inspired by their determination.

"Marathons in different cities are also different," continued Yu, noting that running itself is pleasurable because it offers an opportunity to feel a city's culture. "When you are exploring the city directly with your feet, what you could get is completely different from what you would normally get."

Yu and four members of his club flew from China to New York for the race. He completed the marathon in five hours and 11 minutes.

The number of runners within the Chinese-speaking world, both inside and outside China, has been rising as people's health-awareness grows. Support from celebrities such as Hollywood star Jet Li helps, too.

Running is about "persistence, simplicity and happiness", said Li Wen, a marathon participant from Shanghai.

Long-distance running changed the life of Andy Zhang, a New York-based hedge fund manager.

"Before running, I felt that I had done nothing special in my life," said the father of two. "I joined running partly because of my midlife crisis."

He also experienced great difficulties at first and couldn't make the first mile. After one year of training, however, he felt dramatic changes in his life: a 70-pound weight loss and several new friends with the same interest in running. He finished his first New York City Marathon on Sunday in three hours and 11 minutes.

Wilson Kipsang of Kenya won the men's race, and his compatriot Mary Keitany won the women's competition. Kipsang finished with an unofficial time of two hours, 10 minutes and 59 seconds for the $100,000 top prize. Keitany won the women's contest in 2:25:07.

As for Woo, in addition to the two New York marathons, he has finished seven half-marathons.

"I feel so happy and I feel so accomplished," he said.

Around 0.5 percent of all New York marathon participants are over age 70.

"The world's oldest marathon runner (Fauja Singh of India) is over 100 years old, and I want to break his record," said Woo.

Lu Huiquan in New York and Reuters contributed to this story.