There aren’t many contests that make a 26.2-mile marathon seem like a stroll in the park, but an endurance race in the extreme heat and cold of the driest places on Earth does that and more: It’s a tribute to human conditioning, endurance, and sheer will. The documentary “Desert Runners” follows four individuals who are set on achieving the "Grand Slam," finishing four races in the 4 Desert Ultramarathon in single year in four unforgiving settings: Chile’s Atacama desert, the driest on Earth; China’s Gobi desert, the windiest; Egypt’s Sahara, the hottest; and Antarctica, the coldest.

Filmmaker Jennifer Steinman’s cameras zero in on Dave, 56, an Irishman who began running at 40; Ricky, 33, and American expat in London and former college athlete who took up running to get back in shape; Tremaine, 40, a British Special Forces soldier turned security specialist and recently widowed single father; and Samantha, 18, an Australian law student who wants to be the first female and youngest person to complete Grand Slam, all four testing themselves to the limit as the unforgiving environment tests them. Steinman, who is currently developing “a biography, a dance project and a social issue film” but ultimately immerses herself in one story at a time, explains how she brought their stories to life.

How did you first hear about the desert runners?

Jennifer Steinman: In October of 2009, I went to a conference on health and nutrition where one of the guest speakers was a silly, wacky Irish guy named Dave O’Brien. At this conference, Dave announced to the audience that at the age of 56, he was going to try and run the 4 Deserts Ultramarathon Series, one of the most difficult endurance challenges in the world. I was struck by Dave’s announcement. Just one week earlier, I had been at the hospital with my mother, who had been very ill for a few months. Dave was not much younger than my mother and yet my mom didn’t think she could walk around the block. What made this guy think he could run 1000 kilometers through the desert? I became immediately interested in this difference in perceived limitations that human beings seem to have: how can one person think something like this is totally possible, when most others would perceive it as impossible? And are our perceived limitations actually real, or just something that we arbitrarily decide for ourselves?

I was drawn to Dave immediately because he has an irresistible personality. The first time I met him, I immediately thought, “Now this guy is a character!” Then once we got to the first race we went about trying to find more characters, in part because we weren't entirely convinced that Dave would finish. We talked to anyone and everyone we met, and our other three characters soon made themselves apparent. We met Ricky in Atacama and liked him a lot. He was open and we were drawn to him and because Ricky had done one of the races before, he was a helpful guide and gave us an insider's perspective to the nuts and bolts of the race. Samantha and Tremaine we got to know in the Gobi Desert and both of their stories jumped out at us there and developed in ways we could have never expected. Dave, who we began with, kept pushing himself beyond what we imagined possible and we loved following his journey as well as everyone else's. They each had a unique motivation for why they wanted to run these races, but they certainly shared a common drive and hunger to push themselves beyond any regular challenge and a desire to attempt something extraordinary in remote and beautiful parts of the world.

In general, I am always looking for people who have an interesting life situation and/or story, but who are also going to be comfortable and authentic in front of the camera. They need to be honest, relatable, and most importantly willing to be vulnerable and share themselves openly with us. Our runners were all willing to let others witness their lives at the most raw and intimate moments, and they were able to live it all and talk articulately about it at the same time. As a filmmaker, those are dream characters!

What was your approach going into it?

Originally, I only had enough funding to go to the Atacama Desert and I really had no idea what these races were all about, so it was just an “exploratory shoot,” to see what was going on out there and to follow Dave on his remarkable adventure. I had always wanted to go to Chile. I thought we would just go, shoot a bunch of interesting footage, and maybe post it on YouTube or we got home, and that would be it. But we became so enamored and passionate about the potential of Dave and all the other characters we met, that we found a way to fund the rest — each race just in time.

What were the challenges of filming — logistical, practical, weather, etc.?

It's extremely difficult to shoot under these conditions. We had very minimal equipment. We were lucky that our camera never broke though we had some close calls. Sand was our biggest concern and the camera got stuck a few times but we were able to fix it ourselves. Protecting ourselves from the harsh conditions was also very challenging. I was generally more concerned about our physical safety and our hydration than anything else.

Did you have multiple cameras following the competitors on the course?

We had two cameras with us. My cinematographer carried one and I carried one, and we recorded sound and picture ourselves. While this was extremely difficult, it meant that we gained the trust of our characters almost immediately and throughout the races. We spent a lot of time on foot, in the landscapes but also had the use of 4-wheel drive vehicles when they were available. Although the drivers were all locals ‚ sometimes they spoke English, usually not. Sometimes they knew where they were going, and other times ... we spent a lot of time getting lost in the desert!

Did you come away with a new appreciation for Mother Nature?

I have always had a deep appreciation for Mother Nature and worry for people who think they are in any way a match for her. I think we were all reminded of our place in the scheme of things, and you couldn't help but be in awe in all four of these locations.

What were the most significant things you learned, especially about determination and human will?

I think the biggest thing I learned was that the difference between the people who make it and who don't ultimately has nothing to do with physical fitness. The people who finished the races differentiated themselves by their extraordinary willpower and mental strength, rather than their physical abilities. The one thing that the people who finished all shared in common was the unwavering belief that they would.

Did the experience change you in any way, as it has the participants?

I think I have a higher tolerance for pain and expect more from myself than ever before. And I learned that we can all accomplish so much more than we often think we can, we just have to believe that it is possible.

What reaction have you received so far?

The response to the film at festivals and around the world has been tremendous. As a filmmaker, you can only hope that your audiences will love your subjects as much as you do and it has been thrilling to share the film with such enthusiastic and complementary viewers. Ultimately, this film is so much more about running. It's really a story about setting your mind and what it takes to complete anything difficult, and I hope that people will enjoy the film and be inspired to push themselves further.

Desert Runners” will play in select California theaters this weekend and will be available via Video On Demand, Amazon and iTunes on Dec. 10.

'Desert Runners' race against Mother Nature
Athletes test the limits of the human body in the most extreme places on Earth.