An Interferential Unit is not a commonly heard term, so what is an Interferential Unit? This is used in Interferential Therapy, which a type of Physical Therapy which uses electrical signals for the treatment of spasms and strains. It works like a massage and this stimulates the body to produce endorphins which are known to be natural pain relievers. Due to the action of the endorphins, the spasm in the muscles get relieved, which in turn promotes healing of soft tissues.   Usually, if the affected area has cuts or infections, Interferential Therapy is not used till the cut is healed or the infection has been cured.

The Interferential Units used for the therapy were first developed in Europe during the early 1950’s by Dr. Hans Nemec.  He theorized that two medium frequency AC currents, each with a slightly different frequency, would by their in and out of phase relationship due to the alternating current, produce a third but deeper acting frequency, which promoted healing. This is the principle of the Interferential Therapy.

He proposed that one of the frequencies be kept at a constant 4000 Hz and the other is variable from 4001 up to 4250 Hz. This method of Interferential Therapy was known as ‘true interferential frequency difference interferential’. A different approach was invented, known as the ‘pre-modulated interferential’. In this method, both the outputs were kept at 4000 Hz, but the Interferential Unit could produce perfectly synchronized bursts of frequency with the same polarity simultaneously. This was the pre-modulated interferential and had the same effect of producing a third frequency at a deeper level of soft tissue to help healing.

Clinicians after studying both methods prefer the pre-modulated technique. This is due to the fact that the ‘true interferential’ provides an uninterrupted and constant 4000 Hz frequency to the tissue. Due to the Widensky inhibition effect, the nerve fibers below the electrodes would develop numbness and due to this the patient would feel as if the current has been reduced. In the ‘pre-modulated’ method, the frequency burst occurs within the Interferential Unit, the Widensky effect does not occur. Therefore for the same current, the ‘pre-modulated’ Interferential can treat a larger area with the same treatment frequency.

Since a current is being applied to the body, safety issues are important while operating the Interferential Unit. All manufacturer instructions given with the Interferential Unit should be followed. Improper application of current may result in tissue damage. The Unit has carbon rubber electrodes and for it to conduct the current, water soaked sponges or conducting gel has to be used on the affected tissue. Water alone is not preferable since it may be concentrated in one spot on the electrode and be relatively dry in other places and this leads to improper conduction of the current. The electrodes must be cleaned at periodic intervals to see that the surface is clean so that the current is conducted properly. The modern trend is to use self adhesive electrodes since they are easy to use and can be discarded.

The treatment time and frequency of current applied, varies with different manufacturers. For acute pain, current frequency in the range of 80 Hz to 120 Hz is used. For chronic pain, lower frequencies up to 10 Hz are used. Where there is an acute edema the preferred frequency is from 1 to 15 Hz. In some of the Interferential Units, to give immediate relief to acute pain, an output frequency of 4000 Hz is used as a nerve block. This gives instant relief to the patient. The treatment time for different types of pain varies from 10 to 20 minutes.

Interferential therapy should act like a smoothing massage and so the current should not be too strong to cause discomfort to the patient. When starting treatment, using patient feedback, the comfort level of intensity of the current can be established and the current should not be increased beyond that level. Injury and further pain to the patient can be caused by wrong usage of the Interferential Unit and this should be avoided at all costs. One common type of injury due to improper use of the Interferential Unit is burns to the skin.

In recent times, Interferential Therapy is gaining popularity in the US. When used correctly, it provides a safe and reliable treatment for the relief of pain. With increased use, more and more people are coming to know what is an Interferential Unit and how it works.

If you are interested in a Interferential Therapy unit which can be used in the home, then take a look at our review of the LG-Quad Combo Tens Unit.