Keeping active is known to add years to a person's life. A study by Sweden's Karolinska Institutet, published in August in the , tracked 1,800 people aged 75 years and older for more than 18 years.

It found that those who maintained a healthy lifestyle - that is, those who didn't smoke or drink, participated in a leisure activity and maintained a social network - lived, on average, five years longer for women and six years longer for men. Of the leisure activities, physical activity was most strongly associated with survival. On average participants who swam, walked, or did gymnastics regularly lived two years longer than those who did not.

Globally, life expectancy has risen in the past 30 years, according to World Health Organisation statistics. In 2009, global life expectancy at birth was 68 years, four years higher than in 1990. High-income countries tend to have higher life expectancy; in Hong Kong it's now 86.7 years for women and 80.5 years for men, according to the latest government figures.

So it's not surprising that there are now more age-defying athletes such as Leung.

Kor Hong Fatt, 80, began running at age 71 after a heart attack that served as a wake-up call. Losing his health so suddenly was a shock: "I could not accept that this could happen, since I was physically fit for a man my age and was not suffering from any chronic disease."

Running was a way to get fit, to avoid becoming a burden on his family. "I wanted to prove that my body could take it," says the Singaporean, who is a full-time carer for his wife, a stroke victim. Kor has run 16 marathons since. Last year he qualified for the prestigious Boston Marathon and was the race's second oldest finisher in five hours, 13 minutes and three seconds.

It's never too late to start. Taking up sport later in life, even if a person has been sedentary in prior years, can reverse the effects of ageing and significantly modify risk factors for disease.

Nearly 2,000 people born in 1920 and 1921 were assessed at ages 70, 78 and 85 in a study published in the September 2009 issue of the . Compared to the sedentary, up to 17 per cent were less likely to die between the ages of 70 and 88, were more likely to remain independent and experienced fewer declines in their ability to perform daily tasks, and reported fewer new instances of loneliness and poor self-rated health. The benefits associated with physical activity were observed even in those who began exercising between ages 70 and 85.

Another study, the Dallas Bed Rest and Training research by University of Texas Southwestern Medical School researchers, has tracked five healthy volunteers since they were 20-year-old college students in 1966. That year, their fitness was assessed after an eight-week training regimen following three weeks of bed rest.

A 30-year follow up study, published in 2001, looked at the effect of age on the men's fitness. While all five remained healthy and none required long-term medication, the men gained an average of 23kg and their average body fat doubled to 28 per cent. Their cardiac function suffered: resting heart rate and blood pressure rose, while maximum pumping capacity fell.

The men were put on a six-month progressive endurance training programme that included walking, jogging and cycling. By the end of six months, they were exercising four or five times a week for a total of about 4½ hours. The men averaged weight loss of only 4.5kg, but their resting heart rate, blood pressure, and their heart's maximum pumping abilities were back to their baseline level from age 20. "We reversed 30 years of ageing with six months of training," says one of the researchers, Dr Benjamin Levine.

However, the men were unable to match their peak performance at age 20. It's not surprising, however, because, from age 40, one's maximal aerobic capacity begins a steady decline, dropping by as much as 10 per cent per decade. This is due mainly to the stiffening of the heart and loss of muscle mass with age.

But performance doesn't rely on only physical power. "While you can never again have the speed, strength or balance of youth, mentally you become a lot stronger with age," says Robert Hutchinson, 70, who has done 28 ultramarathons since age 60. In March this year, he completed his third Gobi March, a 250-kilometre, self-supported, multi-day stage race across China's Gobi Desert.

Next up is the Hong Kong 100-kilometre trail race in January, for which he trains up to 100 kilometres a week.

The so-called golden years can be a time to get stronger through resistance exercise, say University of Michigan researchers. Normally, adults who are sedentary past age 50 can lose up to 180 grams of muscle a year.

Resistance exercise - body weight exercises like squats and push ups or Pilates - can increase lean muscle tissue and strength even for those in their 80s and 90s, say the researchers.

The reported last year that after an average of 18 to 20 weeks of progressive resistance training, adults can add 1.1kg of lean muscle to their body mass and increase their overall strength by up to 30 per cent.

It's really a matter of use it or lose it. Consistency is key, says Klaus Köste, 69, the 1972 Olympic gymnastic champion in the vault. "You must move every day." The German gymnast, who had heart surgery in 2005, still trains on the parallel bars daily. "Doing a handstand, for me, is like my medicine."

It's also about being conscientious in all aspects of good health. "You must continually eat good food, drink plenty of water and not too much alcohol," adds Köste.

Finding a good training partner helps. Köste and his wife, also a gymnast, train young equestrian vaulters (who do gymnastics and dance while on horseback) and share their passion for the sport.

But there are challenges for senior athletes. Recovery is the biggest obstacle. "Rest becomes more important as you get older," says Hutchinson.

He often takes up to three complete days of rest after a long training session. But he says he copes with aches and pains better now he is older: "I see them more as a sign of accomplishment."

Leung, who holds the Chinese national record for the 100-metre butterfly in the 60-64 age category, overcomes aches and pains with massage. "I get lots of massages and practise yoga regularly. It really helps with restoring your muscles," she says.

There are many ways to get healthy as you get older. But Kor notes that it's important to listen to your body and stay within your limits.

"Avoiding injuries is important, because it takes more time to heal the older you get," he says. "Try to avoid running in the dark, and be constantly aware of potholes, kerbs and slippery surfaces. I usually run on asphalt and flat surfaces, and try to avoid unfamiliar routes."

While Kor has had his share of struggles, crossing the finish line makes it all worth it. "There are no words that can adequately describe the joy it brings to my heart and soul," he says. "Every time I finish, I am simply euphoric. I have never felt this fit."

Running gives Hutchison a new-found appreciation for the world around him - it's almost a new lease on life, he says. For Chau, being in the best shape of her life brings a sense of self-worth. Competitions give her the opportunity to travel and make new friends.

As George Bernard Shaw said: "We don't stop playing because we grow old. We grow old because we stop playing."

So, what's your excuse?