They're known as Iron Man events, a fearful triathlon of three mile swim, 112 mile cycle race and marathon run.
Britain's number one isn't just any old iron man, however - he picks up his old age pension in May.
For Arthur Puckrin, indeed, the iron man triathlon may be little more than a ferrous wheel. He's also just become world champion at something called the decabiathlon - 1,120 miles on his bike followed by 262 miles on the road, completed with snatches of sleep in 12 days, seven hours and 57 minutes.
In the marvellously masochistic iron mantra there's now talk of a duo-decabiathlon. "I would certainly consider it," he says.
The amazing Puckrin, who left school with two O levels and was called to the bar at 28, has also represented Great Britain at bridge and played in two world and eight European championships.
It's the classic card game, he insists, which takes more out of him. "Bridge is every bit as demanding, probably more so, than the triathlon. It's certainly more vicious.
"In iron man events everyone encourages one another, in bridge it's the opposite. Bridge players hate to lose."
Other - some might say wiser - counsel has urged m'learned friend to take life a little more slowly. Arthur Puckrin, however, remains a law unto himself.
Inevitably asked why, he replies only that it's there, that he enjoys it and that his ambition is to win another world title this year.
He's a Middlesbrough lad, ran to school when others caught the bus, played rugby for the Boro, always wanted to be a professional sportsman and finally cracked it when he was 58.
Running was cheap amusement for a working class family of four children. "We had nothing and all you needed was a vest, a pair of shorts and some sandshoes," says Arthur, though he hesitates at an Alf Tupper analogy.
"I was very much into Alf Tupper and Wilson of the Wizard, but unfortunately no one's heard of them now."
Though neither of his parents had sporting instincts - "I think my Uncle Charlie might have run in the 100 yards at the school sports" - his two brothers also became outstanding distance runners and his sister holds the women's world record for 1,000 miles.
Better known as Eleanor Adams, now Mrs Robinson, she also received a Guinness Book award for breaking more records than anyone else in history.
Arthur lives with his wife Mary in Acklam, Middlesbrough. Since the garage overflows with sports equipment, his canoe is docked on the stairs.
Canoe? In 2001 he won the annual race from Durham to Finchale Abbey and would have won last year's had he not hit a rock with 50 yards to go.
A stop watch sits on the arm of the sofa, his weights - pumping iron man? - next to a pile of law books on the floor. His bike ("cost more than my car") is away being repaired after the decabiathlon and may mend quicker than he is.
"Saddle sores were the worst thing," he says. "I packed lots of nappy cream but I'm still surprised at how long it's taking."
Trophies abound - though it's only seven years since he resumed competitive sport.
"Even when I wasn't competing I was a great believer in daily training," he says.
After school he became a police officer, studied an A level correspondence course while on night shift ("I was wasting my time as a policeman") and after qualifying as a barrister specialised in company law for Dorman Long - "if it hadn't been for nationalisation I'd probably have been running it now," he says.
Instead he began his own law firm - "I was happier on my own" - and when training allows, still practises.
Long distance running had begun with the Lyke Wake Walk, the 42 mile North Yorkshire moors route between Osmotherley and Ravenscar. "In those days it was still long heather, map and compass and watching out for shells at Fylingdales."
His ten hour crossing was a record at the time. His 13 hours 50 minutes for a double crossing was only recently beaten and his 27 hours for a three way attempt has stood for 35 years (and is likely to, it may be added, for another 35, an' all.)
At 30, a heel injury compelled his retreat from front line athletics - though there was still bridge to cross.
Swimming - "I did a length and was gasping" - came much later, cycling after he'd not been on a bike for 35 years.
His heel improved greatly after consultations with a faith healer - "you'll try anything" - though he's uncertain of the real reason for his recovery.
The decabiathlon was in Monterrey, Mexico - "industrial, a bit like South Bank, only bigger" - and would have been a decatriathlon had he not fainted in the pool after an hour, dragged out and subjected to multiple medical indignities which convinced the doctors that he'd had enough.
It was some sort of virus. Against doctors' orders he gained a decabiathlon entry - against 18 others, all much younger - half an hour before the start.
Most subsisted on high tech protein foods; Arthur survived on chicken sandwiches. "They don't do fish and chips in Mexico, and most of their food is inedible."
The 1.2 mile circuit was around a park, cycling in one direction, running in the other, wearing winter gear as protection from the sun and watching out for ducks by day and cats (which came to eat the ducks) at night.
Though going round in circles, or something geometrically similar, there was no danger - he says - of going completely round the bend. "You just think about the next sleep, never about the next event. You'd be surprised what a difference it makes, going round the other way."
He'd begun in walking boots, switched to size 12 trainers because his feet had swollen so much, finished wearing one boot and one trainer.
"It was sheer agony just putting one foot on the ground but in Mexico I was a big television star.
"It's only in Britain, where these things originated, that no one has any interest."
Though fast approaching 65, he plans to run and run - including a double iron man at 7,000ft in Ecuador when he should really be in the post office queue in Acklam.
Advice to anyone contemplating such ultra-athleticism? "Enjoy it as I have, every minute.
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