Rather than type every letter, a more efficient system is to represent sounds with keys. This is how stenography works. Each stoke of the keys is mapped to a series of characters; a letter, a grouping (such as 'sh' or 'ing'), or a complete phrase. Using such a system would allow one motion, for example for 'b', to map to a whole word, such as 'be'. Something as simple as that would reduce your risk of injury by something like 50%.
A major difference between stenography and typing is that steno is chorded: the signal is sent when the keys are released, not when they are depressed. I'm not sure how that would work with the full body.
Check out the OpenStenoProject for more about steno. Their community would probably enjoy discussing a full body steno theory (if they haven't already) .
Take care and thanks for all the effort that went into producing the video! It was a lot of fun :)