The basic principle of Interferential Therapy (IFT) is to utilise the strong physiologicaportable iftl effects of low frequency (<250pps) electrical stimulation of nerves without the associated painful and somewhat unpleasant side effects sometimes associated with low frequency stim.To produce low frequency effects at sufficient intensity at depth, patients can experience considerable discomfort in the superficial tissues (i.e. the skin). This is due to the impedance of the skin being inversely proportional to the frequency of the stimulation. In other words, the lower the stimulation frequency, the greater the impedance to the passage of the current & so, more discomfort is experienced as the current is 'pushed' into the tissues against this barrier. The skin impedance at 50Hz is approximately 3200* whilst at 4000Hz it is reduced to approximately 40*. The result of applying a higher frequency is that it will pass more easily through the skin, requiring less electrical energy input to reach the deeper tissues & giving rise to less discomfort.