Interesting. Sounds like it's fraught with difficulties. I claim ignorance here, but I still am a bit skeptical. I guess if the frequency characteristics are much different from the other muscles. My initial reaction is that impedance changes would confound changes in bio-electrical activity, and that you almost need a DC amplifier for those low frequencies (~0.05Hz). The amount of artifact from various places like ECG, pulse, breathing, swallowing, skeletal muscles, and movement must create a very small signal-to-noise ratio. I'd like to read more about this. thanks for bringing it up.