1. An electrotherapy system including a two-channel electromuscular stimulator and two-channel electromyograph system for simultaneously applying two stimulation signals to a skin area and for measuring stimulation effects in the same skin areas without interference which comprises: a first electromuscular stimulator channel, comprising: means for applying at a predetermined skin location a first varying electromuscular stimulator electrical signal having a variable output pulse rate, a variable on and off pulse rate and a frequency limited to below about 80 Hz; a second electromuscular stimulator channel, comprising: means for applying at said predetermined skin location a second varying electromuscular stimulator electrical signal having a variable output pulse rate, a variable on and off pulse rate and a frequency limited to below about 80 Hz; means for controlling said output pulse rate of said first and second electrical signals; means for controlling output pulse intensity of said first and second electrical signals; means for controlling the on and off pulse rate of said output pulses; a first electromyograph section comprising means for receiving, from a location at generally the same skin area as the area to which said first and second electromuscular signals were imposed, first and second electromyograph input signals corresponding to differences in electrical potential of muscles through the skin of a subject simultaneously with the application of said first and second electromuscular stimulator electrical signals, said electromyograph input signals resulting from said first and second electromuscular stimulator electrical signals; electrical filter means for eliminating unwanted signals and noise from said input signals below about 100 Hz; means for amplifying said input signals and controlling the amplification range of said input signals; means for displaying the intensity of said input signals.