FWIW, WedMD believes it's possible. "Healthy" has nothing to do with susceptibility to hypothermia:
http://firstaid.webmd.com/tc/hypothe...topic-overview
Another useful read:
http://www.***.edu.br/professores/po...Cyrino/A13.pdf
Apparently 1 or 2 runners were evaluated for hypothermia in last month's Los Angeles Marathon. Some were actually taken to the hospital, although the author of the article doesn't bother to find out whether or not they were medically diagnosed as such. I'm guessing the LA Marathon medical staff didn't write off hypothermia simply because many of the event participants were probably 'healthy adults.'
http://latimesblogs.latimes.com/spor...pothermia.html
Swimming comes to mind as the obvious activity in which one could become hypothermic. This article states, "Surprisingly, even well conditioned, properly trained and experienced English Channel swimmers have suffered unexpected fatalities even within relatively short periods of 5-6 hours after the onset of their swim and in water temperatures of 20C. Individual tolerance is highly variable and can be significantly diminished when conditions are poor such as cold ambient temperature and rough weather. Bad weather can lengthen the duration of the swims inducing extreme fatigue and exposure. Prolonged swims in water temperatures below 16C (60F) particularly when the ambient temperatures are low and in absence of sunny conditions could lower the resistance and tolerance of the individual swimmer and might explain adverse outcomes."
http://www.doversolo.com/hypothermia.htm
I'm going to go out on a limb and state that Jackson Stewart, when he abandoned the Tour of California in 2008, was a reasonably healthy adult:
http://www.bicycle.net/2008/hypother...ed-to-hospital
And I suppose if those links don't provide any valuable info, try this one, and 'have it your way."
http://www.youtube.com/watch?v=CJMsFGH4eoQ
Amazing what a guy w/ no medical training, other than lots of first aid, can do with Google.
