Mario Kart, only with bikes instead of karts, and nothing instead of bikes

As part of a UCSB/Harley-Davidson film contest, Michael Figge and Jess Riegel shot this incredible stop-motion video about a race on invisible motorcycles. At first, it doesn't seem very Nintendo-ey (Nintendoughy?) but then, it suddenly becomes a Mario Kart homage. We heart stop-motion.

We'd love to know how they are sitting like that in every frame. Are they being held up by something? Are they sitting on something that was digitally removed from the picture? Are they just very precise jumpers? Watch the video after the break and formulate your own theory!