Friends call him "a freak of nature". John Weber says he is simply lucky to have inherited good genes.
This morning the 75-year-old endurance sport addict will plunge into Acacia Bay for a four-kilometre swim to Four Mile Bay for the 50th Across Lake Taupo swim.
The swim, first held in 1964, has attracted about 400 entries, many of whom - including Dr Weber - will be using it as a final preparation for the Taupo Ironman next week.
It will be his third Across Lake Taupo swim, in which he is the oldest competitor, and his 17th Ironman event around the world.
The former Cornell University medical college professor, from New York, took up endurance sport when he retired five years ago.
"It was part of my retirement agenda. I didn't want to sit at home. I'd run marathons for 10 years before, but wanted something more challenging.
"Friends call me a freak of nature. I've always been healthy and led a healthy lifestyle.
"So when people ask what I do, I choose my answers very wisely. I say I have good genetics - genetics are an important part of being able to complete endurance events.
"You also have to do a lot of hard training. You are always going to feel pain.
"The thing is to differentiate between pain from fatigue, and pain from injury.
"Endurance sport is like gambling - it is an addictive behaviour. You develop a tolerance so you increase the distance each step until you reach an Ironman level."
Dr Weber is 20 kilograms lighter than when he was working, and has a resting heart rate of about 40 beats a minute. "I don't have any defects of any sort, I have a good heart, good muscles, good leg strength. Sadly, some people don't have this."
He also has another reason for competing in the lake swim.
"It's a place I can come to escape the New York winter."
He arrived in Taupo in December, after leaving home in August, competing in endurance events along the way.
He will be back home in a fortnight. "My grandchildren think I have gone to Mars."
- The Dominion Post
Who do you think won Key v Cunliffe's second debate?Related story: Leaders debate reveals more even contest