Interferential therapy was developed by Dr. Hans Nemec in 1950. It was suggested that the use of two medium frequencies has the advantage of reducing skin resistance.

Z = 1/2πfC

Where Z = Impedance

            f = frequency

            C = capacitance

When the frequency increases the skin resistance decreases. So the interferential therapy is used to treat the deep pain, idiopathic pain, relieve edema, control stress incontinence (inability to control urine) by stimulating pelvic floor muscles.

The current is produced by mixing two medium frequency currents delivered to skin through two sets of electrodes through separate channels in the same stimulator. One current is normally of fixed frequency i.e. 5000 Hz while the other frequency is variable i.e. 5200 Hz. The two alternating currents interact with each other. When they are in the same phase higher amplitude is produced and lower amplitude is produced when the currents are in opposite phase. The interaction of two medium frequency currents produce envelops of pulses known as beat frequency. Beat frequency will be the subtraction of the two medium frequencies.

The increase in the blood circulation which may be produced by either pumping effect of the stimulated muscles or the effect on the autonomic nerves of blood vessels and therefore remove the chemicals from the area which stimulates nociceptors. Low frequency currents with short duration (at frequency of 100 Hz (5200 – 5100)) stimulate large diameter nerve fibers which will have and affect on the pain gate and inhibition of transmission of small diameter nociceptive traffic.

In order to selectively activate the descending pain suppression system with a frequency of 15 Hz (5200 – 5185) which stimulate small diameter fibers eventually will cause the release of endogenous opiods.

Normal innervated muscle will be made to contract if the interferential therapy is 1 – 100 Hz is used. The type of contraction depends upon the frequency stimulation. At 1 – 5 Hz tickling (minimal contraction) sensation is produced. Muscle twitch is produced at 5 – 20 Hz. Partial tetanic contraction is produced from 20 Hz up to 30 Hz. And from 30 – 100 Hz complete tetanic contraction is produced.

The complete range of all contraction will be produced when rhythmical frequency between 1 – 100 Hz is used.

Exudates is accelerated by a frequency of 1 – 10 Hz with rhythmical pumping action is produced by muscle contraction and therefore is possibly an effect on autonomic nervous nerves which can affect the diameter of blood vessels and therefore increased blood circulation. Both factors help in the removal of exudate.

It is useful in wide variety of painful conditions (Acute, Chronic, Deep, Idiopathic, Subacute pains etc) AMF (Amplitude Modulating Frequency) 70 – 150 Hz is used for Acute Pain. Frequency below 50 Hz is used for chronic pain and subacute pain where muscle contraction is required.

Frequency of 1 – 10 Hz is used for to reduce oedema i.e. oedema of hand and feet.

Quadripolar technique:

Two electrodes are placed on lower abdomen while the other two are placed on inner upper thigh. This technique is used in stress incontinence.

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