In my seminars where I demonstrate applied and behavioral kinesiology (muscle checking), I talk about how we are electric systems and how we produce 22 millivolts of electricity within our bodies.
A blurb in DISCOVER MAGAZINE reported that scientists at the California Institute of Technology discovered long strings of our DNA carry electricity.
They speculated that these strings of DNA may be the equivalent of our interstate system carrying messages from one gene to another located at an exit ramp. So, my speculation would be that the muscle checking is tapping into this highway and giving us immediate feedback on what's going on inside us.