It turns out the electrical potential or electricity that you can measure on the surface of the body reflects things that are happening deeper inside like the beating of your heart.

人们已经证明在体表测量得到的电势能,或者电信号,能够表征,像心跳这样,身体较深处的变化

耶鲁公开课 - 生物医学工程探索课程节选