Note the vest: "Blind Skier" - i.e. Mark on the left. Pete (co-organiser) does volintary work skiing with blind people. Together they've developed a "beat box" plays a selection of music overlaid with a regular rythmic beat, and which is worn on Petes' back. The beat (mainly) is what Mark uses to guide him.
I was following these two on my snowboard and was having a hard time keeping up. At the bottom Mark's GPS reported (verbally) a top speed of over 50km/h! Amazing and inspiring.