Most people would consider running a 500km ultramarathon daunting. But 62-year-old Lim Nghee Huat thought it just wasn't enough of a challenge.

In July last year, the media producer astounded the SG50 Steering Committee by announcing that he would run five times that length to mark Singapore's golden jubilee and honour late founding Prime Minister Lee Kuan Yew.

Mr Lim initially planned to run 500km, but later decided that it was "not too difficult" and wanted to do more to push himself.

From April to June this year, Mr Lim and fellow ultramarathoner Yong Yuen Cheng ran 2,500km in 50 days - or 50km daily for 50 consecutive days - a feat so epic that they said they have yet to fully recover from it.

Mr Yong, a 44-year-old physical education teacher, said: "We wanted to make an impact, to let younger generations know that our country is going to face a lot of challenges, even after 50 years of nation building.

"What can bring us further is the character and resilience of our youth. We hope we have conveyed some of that spirit to them through what we did."

The two men met a decade ago when Mr Lim was searching for candidates who could take on the Nanyang Technological University (NTU) ultramarathon in 2005.

An ultramarathon involves distances longer than the usual 42km marathon.

Hearing from his son's friend that there was a physical education teacher who might be up to the mark, Mr Lim made a trip down to Kallang River to seek out Mr Yong, who was coaching a school canoeing team there.

"I was very honoured," said Mr Yong, who came in second in the NTU ultramarathon, on Mr Lim's heels. "He is more senior than me, yet he is still so passionate about running at his age."

Years later, when Mr Lim asked if he would join him for the SG50 run, he said "yes" at once.

Both ultramarathoners, who have been running since they were 17, knew that this gruelling attempt would be unlike anything their bodies had ever encountered. Said Mr Lim: "I thought it was Mission Possible, but every day, there was a high chance we would not be able to finish."

Mr Yong strained his Achilles tendon two weeks into the run, but there was no time for him to recover from the injury.

"Every day when I went home, my mother asked me why I still wanted to continue. It became quite difficult to face my loved ones," he said.

Mr Lim also endured a severe bout of diarrhoea and vomiting at the halfway mark, and had to rush to the toilet several times along the route.

He recalled: "I was in so much pain. That was the only time on the run that I cried."

They drew strength from the support of members of the public - ranging from former general election returning officer Yam Ah Mee, who joined them in completing 50km, to the fish porridge hawker who recognised Mr Lim and insisted that he eat for free.

For now, both are taking a break from marathons. Mr Yong will resume running marathons such as the Standard Chartered Marathon only from next month.

Mr Lim will be applying soon for next year's Badwater Ultramarathon, an invitation-only 217km foot race in California's Death Valley that he has completed before, and through which he hopes to raise funds for charity again.

Both admit that their SG50 feat will be a hard one to top, but they hope it will continue to inspire more Singaporeans to lead active lifestyles.

Said Mr Lim: "I want to use my running to motivate people to take up sport. If you can adopt a healthy mindset, it will be the best gift to you and your family.

"So many ordinary Singaporeans who had never run marathons before joined us, and some actually managed to complete 50km. That was very encouraging."

Olivia Ho