Futurist and science fiction author Arthur C. Clarke famously said, the only way to find the limits of the possible is by going beyond them to the impossible. An apropos theme for my conversation with Jennifer Steinman, a documentary filmmaker who spent well over a year following four seemingly normal, far from professional athletes as they prepare for and undertake one of the most grueling, backbreaking endurance challenges on the planet — a collection of ultra-distance adventure footraces teetering on the absurd dubbed the 4 Desert Series.

WHAT IS THE 4 DESERTS?

Named by TIME magazine as one of the world's Top 10 Endurance Competitions, the 4 Deserts is the world's leading rough-country endurance footrace series. A unique collection of world-class events that take place over 7 days and 250 kilometers in the largest and most forbidding deserts on the planet.

Jennifer has a more poetic take on this lunatic fringe:

Imagine you’ve been dropped off in the middle of one of the largest, driest deserts in the World. Over the next six days you will have to run, jog, walk or crawl 155 miles through incessant heat, across soft sand and hard-packed gravel, over sand dunes multiple stories high and down razor-sharp rocky cliffs. You must do this carrying everything you need to survive — clothes, food, sunscreen, emergency medical supplies, sleeping bag — in a 20-pound pack on your back.

Now imagine doing this not just once, but four times in one calendar year, through the driest, windiest, hottest, coldest and ultimately the most treacherous four deserts in the world: the Atacama Desert in Chile, the Gobi Desert in China, the Sahara in Egypt … and then, the final stage, a 150-mile footrace across the single most inhospitable landscape in the world: The Last Desert in Antarctica.

Any single race in RacingThePlanet’s 4Desert Ultramarathon Series is an extraordinary, life-threatening challenge– something we would only expect the most accomplished, elite athletes on the planet to try. But most of the courageous men and women who come from all over the world to compete in these Herculean events are not professional athletes at all, they’re ordinary people—people with families and day jobs and mortgage payments– people like you and me who have decided, for a variety of personal reasons, to take on this extreme physical challenge.

Why do they do it?

This week's guest set out to answer this question. The result is Desert Runners– a feature length character-driven documentary that follows a remarkable collection of brave souls on an extraordinary year-long adventure, racing to the four corners of the Earth.