Recently on the market I have noticed a plethora of devices claiming to be "Inteferential" devices. However, the majority of the devices are Symmetrical Biphasic Square waveforms with a carrier frequency for cost containment purposes. All of the research supporting the effectiveness of Interferential therapy that I was able to locate was based on the Sinusodial waveform or "sine wave". Does anyone know what a symmetrical square wave with a 4000Hz carrier frequency will do to the human body? Is this not just a muscle stimulator with a carrier frequency?