I am riveted by extreme sports like big-wave surfing, 'megaramp' skateboarding and half pipe snowboarding. I am fascinated partly because the sports are so exhilaratingly acrobatic. But I am also captivated by the fear that a terrible accident might happen at any moment. And accidents do happen.

My main trick is to work with amazing people. It's a long and twisty journey and you need people that really are amazing and have this rare gift of honesty and courage and really open up.

I'm not an expert on how to configure the sport, but I can observe and say that accidents seem to be a part of it. The athletes are incredible, with the courage that they accept the risk of death, paralysis, and brain injury. These are really life-changing, life-threatening injuries, and the risk is extremely high.

Extreme sports tricks are becoming increasingly complex, the courses ever more challenging and crashes all too common.

I can ask someone to let me into all aspects of their life for several years, but people have got to have that gift: that courage and that talent for opening their lives to the camera. Being candid is a gift, and that's what the audience responds to. Part of it is me asking, and part of it is just their inherent talent, which is what you are looking for when you make documentaries - people that are really going to let you in on what they are going through.

I don't know if people realize how hard I work, because sometimes people ask me for my secret. The truth is that I don't have any secrets apart from the fact that I've been directing theater and film for twenty years and trying at every stage to make my work better.

I think we've reached that point where we understand medically what we are doing to ourselves with these sports. In football, it's kind of hard to get the access that you want for the story and, of course, it's very long-term: the effects of the repeat concussions really don't hit until decades afterwards, whereas the traumatic injuries in extreme sports are very immediate. I realized Traumatic Brain Injury was a fascinating and important story that not had been told very much. I wanted to know more.