Endurance athlete and Badwater Ultramarathon champion Marshall Ulrich, who has run across the country and climbed the Seven Summits, knows how to suffer—and still have fun doing it. Ulrich, 61, along with his firefighter friend Dave Heckman, recently became the first to circumnavigate Death Valley—the hottest place on earth—on foot, unsupported. The pair buried 37 food-and-water caches to sustain them over 16 days and 40,000 feet of climbing in seven mountain ranges. All told, the athletes covered 425 punishing miles in 100-plus-degree heat. Ulrich spoke with Men’s Fitness on how he trained, stayed cool, and ultimately, survived his epic endurance journey across some of the planet’s most unforgiving terrain.

How do you prepare for a brutal trip like this?
I bumped my mileage up to running 100 miles per week. I also trained in Lake Havasu on and off for two months beforehand. Even in May, the temperatures there can get up to 117. So I was training in the heat with a backpack to simulate carrying all that weight. Badwater [just beforehand] was kind of a tune-up, if you will, to put the polish on it.