I've wondered about the filming, but most of the talky bits are obviously filmed by them themselves, and all the long shots of them trudging through the snow could have been filmed during the practice bit before the race and then edited in randomly as, let's face it, one bit of grim featureless frozen landscape is pretty much like another
Am loving it, but loved 'Blizzard' more - 'twas on a year or so ago and re-created Scott and Amundsen's race to the pole - had Bruce Parry in it.