A series of wires attach to the arm and interpret the signals for actions, like air strumming to Guitar Hero, or changing the iPod track.
It can all work by a thin strip that can be concealed under your clothes, and could work with any number of devices like consoles and such. Check out the clip below. It's not something that's hitting the market anytime soon but trust Microsoft to make us want it.
Microsoft trials 'muscle reading' input controller, EMG clip surfaces
05 January 2010 | By Simon Priest