They have come to test themselves in the desolate lava fields of the Kona Coast once again in a race they call the Ironman.
Fifteen years ago, slightly more than a dozen lined up in Honolulu for the first one, and today 1,490 qualifiers from an initial pool of 10,000, from 50 states and 50 countries, are here.
They include a man they call "the Grip," who is trying to win for the fifth consecutive time and possibly break eight hours.
Perhaps the oddest thing about the Ironman triathlon is that as grueling as it is, it is not impossible: In 16 previous events, 13,000 have finished and only 1,000 haven't.
Today, they will line up in the warm waters next to Kailua pier for a frantic mass start to a 2.4-mile swim, a 112-mile bike ride into vicious winds and searing heat, and, finally, a marathon run in 100-degree temperatures.
Says defending champion Mark Allen: "You confront the dark side in yourself that wants to quit."
They call Allen the Grip because once in the lead, he holds on. In his first seven tries, he fell prey to cycle crashes, flat tires, dehydration and heat exhaustion while trying to catch six-time champion Dave Scott.
In 1987, Allen was taken to the medical tent and received five bottles of IV fluid after a duel with Scott.
Then, shortly before the 1989 event, he went for tests at Duke University to analyze his body under stress and found he was especially vulnerable to salt loss.
"That was the last piece of the puzzle," Allen said.
That year he took in extra sodium in his electrolyte replacement drinks and broke away from Scott in the 24th mile of the marathon--running it in a record 2 hours 40 minutes 4 seconds.
Scott subsequently suffered a career-ending knee injury and the rest of the world has been chasing Allen, now 35, ever since.
A training injury to Paula Newby Fraser, 31, five-time Ironman women's champion, has the women's field thinking an upset is imminent.
"My ankle feels fine," said Fraser, whose 8:55:28 last year left her 26 minutes ahead of Canada's JulieAnne White. "But I took three months off from running and a month and a half off the bike. This is the least prepared I have ever been for the Ironman. I just hope my years in the sport and my strength can carry me through."