He finished the 54-mile Caledonian Challenge, a racewalk in hilly Scotland, in June and knocked off the Beijing International Marathon two weeks later. So runner and racewalker Mark Capstick didn't think Hong Kong's 62-mile Oxfam Trailwalker racewalk would be too daunting.

But the 31-year-old State Street Global Advisors bond manager hadn't counted on Hong Kong's sultry 80-degree heat. About 43 miles into the race along the spiky ridges of Mac-Lehose Trail, which spans Hong Kong's New Territories, Briton Capstick began to suffer dehydration. He became nauseated and developed a severe headache, his hands began to swell, and he slumped to the ground. After a quick medical check, he fell asleep for half an hour. When he awoke, he felt better and continued, finishing in a respectable 28 hours and 40 minutes.

"That was the hardest thing I've ever done," says Capstick. "The heat, the terrain, the length -- it is tough." It took a week for his blisters to even start to heal, says the money manager, who oversees $16 billion in fixed-income assets.

Chastened by his ordeal, Capstick has vowed not to enter the Trailwalker again. His London colleagues, aware that he has broken similar pledges before, have hung a photo of him asleep on the trail in SSgA's kitchen.