Bruce Allentuck wants you to know he is a regular guy. He is not a Navy SEAL. He is not a physical trainer. He is a 45-year-old married father of three, owner of a small landscaping business, resident of a pleasant middle-class neighborhood in North Potomac.

Except that he is compelled, for reasons he explains in simple terms, to determine how much punishment he can inflict on his body and mind. That is why he was crunching through six miles of ankle-deep snow in the woods recently, lugging a three-foot, 50-pound length of solid oak. Why he recently ran a third of a mile in nine minutes carrying two 40-pound buckets of gravel. Why he runs five miles in a creek with a 60-pound truck tire slung over his shoulder.

It is why he is the only person from the Washington area headed to Vermont in June to run the 2011 Death Race, the sixth year of a competition so unimaginably cruel that the organizers require the 200 carefully selected entrants to sign a three-word waiver that reads simply, "You may die."

"I just want to see if I can push through and do it," said Allentuck, who has completed seven marathons, four ultramarathons, three Ironman triathlons, a 4.4-mile Chesapeake Bay swim, and 30 to 40 other triathlons of various lengths.

"I've done all kinds of things," he said. "It's the next thing."

Allentuck's personal journey roughly parallels the evolution of adventure racing itself. As the sport's popularity has surged over the past decade, the core disciplines of trail running, biking and paddling are increasingly combined with wades through mud bogs, leaps over fire pits and knee-scraping crawls under barbed wire.

Jack Raglin, who studies the connection between the psychology and biology of exercise at Indiana University, says Allentuck does not exhibit any of the classic signs of exercise addiction: diminished family and social life, loss of interest in anything but exercise, lack of interest in his job.

Instead, he is driven to see what he is capable of.

"It seems to be something people are either born with or develop very early on their own. It can't be coached or taught," said Raglin, a professor in the university's kinesiology department. "They have this need or desire to find out where that limit is. It's obviously very rare."

The Death Race, the diabolical creation of veteran adventure racers Joe De Sena and Andy Weinberg, prides itself on messing with competitors' minds. It is, De Sena says, more "obstacle race" than adventure race. Entrants are not provided food or water. They are not told exactly when the race will start, when it will end, how long it will last or what their tasks will be. They know only that they will be so physically and mentally exhausted that just a small percentage will even finish.

In 2009, racers began at De Sena's Pittsfield, Vt., farm by slithering through mud under barbed wire at 4 a.m. to find their race bibs pinned to tree stumps. They had to hack the stumps out of the ground and carry them for most of the 24-hour race. There were countless hours of running, climbing, bushwhacking, log-splitting and lifting. After a 2,000-foot climb, they found a list of the first 10 U.S. presidents, which they had to recite correctly after running back down the mountain. One mistake and they were sent back up again. The following year, some pre-race instructions arrived in Greek.

"The race emulates life," said De Sena, 42, who bluntly acknowledges that he does everything he can to persuade competitors to quit. "It has no beginning and no end - or at least not a beginning and end that you know of. You don't know the tasks at hand. It's gonna frustrate the hell out of you."