WARTBURG, Tenn. — On Friday night, in the Cumberland Mountains of eastern Tennessee, 28 men and 7 women will lie in tents half asleep in anticipation of hearing a conch shell being blown at Big Cove Campground in Frozen Head State Park. When they hear the call, which will arrive sometime between 11 p.m. that night and 11 a.m. Saturday, they will know they are 60 minutes from the start of an ordeal once referred to as a “satanic running adventure.”

It is a 100-mile footrace that some say is actually 130 miles or more, through unmarked trails that have names like Meth Lab Hill, Bad Thing and Leonard’s Buttslide and that are choked with prickly saw briers. Temperatures often range from freezing to blistering on the same day, and there is a cumulative elevation gain of more than 60,000 feet, or the equivalent of climbing Mount Everest twice from sea level.

A 60-hour time limit forces competitors to run, climb and bushwhack for three days with little or no sleep. They endure taunts from the race director, who deliberately keeps the competition’s entry procedure a mystery. It is a race in which there are no comfort stations, and runners cannot use a GPS device or a cellphone.

Less than 2 percent of the nearly 800 ultrarunners who have subjected themselves to this punishment — 12 men, the same number as have walked on the moon — have finished the race in its current iteration. The only prize is that after 100 miles, they get to stop.