There are people who do amazing things, and some just don't know when to stop.
Take the 48-year-old blind athlete extraordinaire Rob Matthews. Neither age nor disability is slowing him down. In fact, the pace is picking up, to what might be called extreme degrees.
The Englishman, now married to a New Zealander and living in Auckland, has a string of Paralympic running achievements on his CV that mark him down as a legend in this arena, and a prized MBE awarded to him by the Queen in 1987 for services to disabled sport.
A potted biography on his website explains: "Rob has driven a racing car at high speed at Brands Hatch, he skis and plays golf, football and cricket."
The Rob Matthews catch-cry should be: "But wait, there's more."
Matthews, who has also won a 2009 world Paralympic triathlon silver medal for New Zealand, is becoming increasingly well known in his adopted homeland, especially through the release this month of his autobiography Running Blind and television appearances.
His next race is the Auckland half marathon on November 1, where he aims to run 1hr 22m and break his own race record for a blind runner.
This provided the Herald with the opportunity to photograph Matthews in action, training with his running guide Nick Buck, and delve into the world of a blind runner and his aides.
Matthews, who fits his athletic life around work as a sports massage therapist, is also trying to build a profile as a motivational speaker.
Not only is he attempting to represent New Zealand in cycling at the 2012 London Paralympics - his priority for now - but he told the Herald of his plan to take on two world-renowned extreme-endurance races: the six-day 250km Sahara desert charity run known as Des Sables, which usually begins in late March, and the month-long 650km Polar ski-walk challenge from a remote starting point in Canada to the North Pole, in mid-April.
"I'd go from 60 above to 40 below - it would be a kind of crazy thing to do," he says. "I may have to do them a year apart, but I'm thinking about doing one after the other. I'm always up for a challenge."
Little wonder then that the 27-year-old Buck, a former national junior cross country representative and senior 800m bronze medallist, describes Matthews as an inspiration.
"He's given a shitload more to me than I have to him," says Buck, a one-time financial analyst who now runs a juice bar, when asked about his dedication to Matthews' cause.
Buck took up the challenge of being a running guide after Matthews advertised for help.
"I wasn't in a good place when we met, about to quit my job, and my motivation wasn't there," says Buck.
"Rob inspires by example, which encourages you to work with what you have got.
"It was also great for me to be around a serious athlete again, someone who sets goals and really goes after them."
The pair's initial aim was to compete in the 1500m at the Beijing Paralympics but with limited preparation time together, they missed the tough New Zealand qualifying time.
Buck is the 115th running guide that Matthews has had. A chemistry is required for racing and training, which ranges from sprints to long runs. The pair are linked by a short rope and the guide needs to be a quicker runner so it is never a struggle to keep up with Matthews.
"The worst was a guy in England who was too hesitant and in the space of 100m I fell off a kerb, hit a lamppost and bounced off a fence. I didn't run with him again," says Matthews.
Matthews' ace guide is a former British paratrooper Paul Harwood, a man who drives Matthews hard. He would be the logical choice for the Sahara and North Pole expeditions.
Before undertaking those daunting challenges, Matthews is hell-bent on campaigning properly for the 2012 Paralympic road cycling events. The immediate priority is finding the money for a new $16,000 custom-built tandem.
Matthews competed at the national road championships this week with his pilot, Carlos Nichols, but the standard touring tandem didn't last an 80km race after the back wheel buckled. Getting a new bike, and doing well at the next two world championships, is paramount to his hopes in London.
If it works out, it would be a poignant return home for Matthews, who was raised in Strood, Kent.
Matthews inherited the degenerative eye condition retinitis pigmentosa from his father. The young Rob Matthews could never see in darkness, and the condition started to badly affect him when he was 11.
It is easy to understand how this battered his confidence and esteem. Matthews' learning was affected and he could hardly see the footballs he wanted to kick. At 13, life started to turn around when he attended a school for the partially sighted, at 15 he learnt Braille, and a year later started at a college for the blind.
"I began to come to terms with losing my sight," says Matthews, whose two sisters are sighted. "I'm often asked if I was struck by fear but I can't remember being really frightened as such.
"I certainly felt sorry for myself and wondered why it had to be me. I'm glad it was, because I certainly wouldn't have had the life and experiences I've had. Blindness enriched my life."
Those experiences include winning 13 Paralympic gold medals for Great Britain, including eight golds, and setting 22 world records. The highlights are a come-from-behind victory in the 10,000m at the 2000 Sydney Olympics, and becoming the first and still only blind runner to break two minutes for the 800m, which he achieved in 1986.
There is a very tragic element to Matthews' life, and one with a strong link to the latest turn in his Paralympics career.
In late 2003, his first wife, Kath, died suddenly. A blockage in the brain had caused pressure which shut off the automatic breathing nerve, Matthews explains, and she died overnight at the age of 38. "I still think of her regularly, every day, and it was the hardest thing I've ever had to face," he says.
"Life can be hard. I guess I'm one of life's survivors, and I don't let things get me down or get in my way but that was the closest that anything came to doing it.
"The running really helped, along with friends and talking about her all the time ... They helped me pull through. I used the 2004 Paralympics in Athens as a vehicle to get me through those first 10 months."
He first started riding a tandem with Kath, touring Ireland and France, and now, at the suggestion of New Zealand's Paralympic officials, he will attempt to win cycling medals at the age of 51 in the London Games.
Eighteen months after Kath passed away, Matthews was on holiday here when he met Auckland interior designer Sarah Kerr - a former presenter of the TV show Changing Rooms - at a waterfront bar.
"We went for a walk and didn't stop talking for 26 hours," he recalls.
"So much happened in the next year - we got married, bought a house, I emigrated four months after we met, and 18 months to the day after we met Thomas was born."
Thomas, 2, can see in the dark, and his parents are optimistic that he has not inherited the eye condition.
Among the Matthews' new friends is Nick Buck, the running guide whose own life has been so enriched by Matthews, who says: "I think Rob does so well because head-wise, he's had to fight pretty hard for a lot of things that we take for granted, and in a lot of areas of his life."