Age is no barrier for some competitors, and crossing the finish line makes all the pain worth while.
Abu Dhabi Triathlon is a generation game for some
When Richard Greensmith received a call from his granddaughter promising a surprise gift on his 78th birthday, the Englishman had little inclination what it was.
He recalled her saying: "I've got a lovely 78th birthday present for you, granddad, but you will need your bike."
He added: "She never said what it was. Absolutely incredible."
• Van Lierde makes all the running on a hot day at Abu Dhabi Triathlon
• Triathlete Joyce glad to finish in one piece
• High drama for Egyptian at Abu Dhabi International Triathlon
• Abu Dhabi hospitality makes challenge worth the wait for triathlete
Greensmith arrived in Abu Dhabi on Friday morning and 24 hours later he was accepting his gift as he cycled in the Abu Dhabi International Triathlon as part of a relay team that included his granddaughter and a friend.
"It is so hot and windy out there, but it's fantastic," the native of Nottingham said after his 50km cycling round, enjoying himself even as others as young as his granddaughter struggled on an unusually hot, 36°C day.
"I did a bit of practice, but not in this heat," he said. "It is only 6°C back in the UK. This is my first triathlon. I only cycle for leisure, normally about 100 miles a week. So this slotted into the right distance - 30ish miles.
"I was just hoping I didn't dehydrate. That's the main thing, because it was so hot."
As the temperature rose through the day, Greensmith was often asking himself why he was out there.
"I could be in the pool," he said. "But it has been a great, great occasion. God willing, I'd love to [do this again]. It's inspired me to have another crack."
John Stewart, 16 years younger than Greensmith, is also looking forward to coming back. He arrived in Abu Dhabi on Friday and will be flying back to the UK's Midlands today after taking part in the Short Course section of the triathlon, which involves 1,500m of swimming, 100km of cycling and a 10km run.
"I have been doing this for 14 years now and I have done about 20 long-course races," said Stewart, 62. "So I started as an old man, but what I like about this is you can compete with people in your own age group, and competing is the name of the game.
"This is my first time here and it is a bit warm for me because I come from a really cold country - raining, cold, wind, snow.
"It was very windy at the back end and loads of sand. It's just too much, but I will come again next year. I will do the long course."
Given his age and the difficult weather conditions, many would question the wisdom behind coming back for the longer race.
"It's the adrenalin," Stewart said. "On the start line, 2,000 other people around you. It's just the lifestyle. I am retired now, so this is what I do for sport. When I finish this, I will take up golf.
"I have never won a race. It's just about taking part, about racing and challenging yourself against the other people, people in your age group. The best part is finishing … a medal on the T-shirt.
"I came on my own and made loads of new friends. I will be going back with some good memories and a few telephone numbers."
While Stewart knows his way around a triathlon course, first-timer John Birk from Syracuse, New York, has learnt some important lessons for the next time. "I never practised all the three events together," said the Abu Dhabi-based expatriate.
"When I was training, I cycled, I swam and I ran, all separate. Putting them together is really difficult.
"So I would say try to put them together before you come to the real event, at least once for practice.
"The bike-run transition was pretty difficult.
"This was my first time and probably won't be my last. It was a good time, good experience. Tests your endurance."
With his stamina put to the test and quitting an easier option, Birk kept urging himself towards to the finish line.
"I was just telling myself not to stop," he said. "That's what you have to do, say 'Don't stop'. It's so easy to stop, but you have to keep telling yourself not to.
"You've got to be a little crazy to do [triathlons], especially the long ones. But the sense of accomplishment is pretty overwhelming."