The basic principle of Interferential Therapy (IFT) is to utilize the significant physiological effects of low frequency electrical stimulation of nerves without the associated painful and unpleasant side effects associated with low frequency stimulation. Interferential therapy utilizes two of these medium frequency currents, passed through the tissues simultaneously, where they are set up so that their paths cross & they interfere with each other. This interaction gives rise to an interference current (or beat frequency) which has the characteristics of low frequency stimulation in effect the interference mimics a low frequency stimulation. The exact frequency of the resultant beat frequency can be controlled by the input frequencies. If for example, one current was at 4000Hz and its companion current at 3900Hz, the resultant beat frequency would be at 100Hz, carried on a medium frequency 3950Hz amplitude modulated current. By careful manipulation of the input currents it is possible to achieve any beat frequency that you might wish to use clinically. Modern machines usually offer frequencies of 1-150Hz, though some offer a choice of up to 250Hz or more. To a greater extent, the therapist does not have to concern themselves with the input frequencies, but simply with the appropriate beat frequency which is selected directly from the machine. The magnitude of the low frequency interference current is (in theory) approximately equivalent to the sum of the input amplitudes. The resultant current will be stronger than either of the 2 input currents. The use of 2 pole IFT stimulation is made possible by electronic manipulation of the currents â€“ the interference occurs within the machine instead of in the tissues. A 4 pole application the interference is generated in the tissues and with a 2 pole treatment, the current is pre modulated i.e. the interference is generated within the machine unit (Ozcan et al, 2004). The treatment effect is generated from low frequency stimulation, primarily involving the peripheral nerves. Low frequency nerve stimulation is physiologically effective (as with TENS and NMES) and this is the key to IFT intervention.
PHYSIOLOGICAL EFFECTS & CLINICAL APPLICATIONS:
IFT works in a special way because it is interferential as opposed to normal stimulation. It is often regarded (by patients) to be more acceptable as it generates less discomfort than some other forms of electrical stimulation.
Pain Relieving Mechanism of Interferential Therapy:
There are 4 main clinical applications for which IFT appears to be used:
As IFT acts primarily on the excitable (nerve) tissues, the strongest effects are those which are a direct result of such stimulation (i.e. pain relief and muscle stimulation) and the other effects are secondary consequences of these.
Electrical stimulation for pain relief has widespread clinical use. The therapist uses the higher frequencies (90-130Hz) to stimulate the pain gate mechanisms & thereby mask the pain symptoms. Alternatively, stimulation with lower frequencies (2-5Hz) is used to activate the opioid mechanisms, again providing a degree of relief. These two different modes of action can be explained physiologically & have different latent periods & varying duration of effect. Relief of pain is achieved by stimulation of the reticular formation at frequencies of 10-25Hz or by blocking C fibre transmission at >50Hz. Both of these mechanisms are proposed theoretically. A good number of recent studies (e.g. Hurley et al 2004, Johnson and Tabasam 2003, Walker et al 2006, McManus et al 2006, Jorge et al 2006) provide substantive evidence for a pain relief effect of IFT.
Stimulation of the motor nerves is achieved with a wide range of frequencies. Stimulation at low frequency (e.g. 1Hz) results in a series of twitches, while stimulation at 50Hz will result in a titanic contraction. On the basis of the current evidence, the contraction brought about by IFT is no better than would be achieved by active exercise for patients who cannot generate useful voluntary contraction; IFT is beneficial as it would be for those who, for whatever reason, find active exercise difficult. Stimulation at higher frequencies than that needed to bring about a partial tetany generate a strong tetanic contraction which are considered beneficial to assist patient appreciation of the required muscle work. Caution is exercised to avoid fatigue due to muscle contraction.
IFT causes muscle contraction which brings about a local metabolic and thus vascular change. Based on current available evidence, the most likely option for IFT use as a means to increase local blood flow remains via the muscle stimulation that occurs due to IFT.
IFT has been claimed to be effective as a treatment to promote the reabsorption of oedema in the tissues. The preferable clinical option in the light of the available evidence is to use the IFT to bring about local muscle contraction(s) which when combined with the local vascular changes that will give result effective in encouraging the reabsorption of tissue fluid.
How does interferential therapy work?
Interferential therapy (IFT) involves the use of low frequency electricity to stimulate peripheral nerves. Clinically this method is used to reduce oedema (abnormal pooling of blood and/or fluids in body tissue), relieve chronic pain, stimulate muscles, and improve blood flow in a target region. These frequencies stimulate a natural pain relieving mechanism called the Opioid mechanism causing pain free pain relief.
Muscles are innervated with motor neurons that can be stimulated by electricity, the lower the frequency the milder the effect and hence contraction. This stimulus can be controlled in a manner that mimics the natural electrical activity of muscles achieved during exercise. This method is particularly useful for physios treating patients who are unable to achieve active exercise for whatever reason as it prevents muscular degradation and is thought to have a strengthening effect.
As discussed above, interferential therapy has its uses in pain relief and muscular contraction. It is used as a technique to achieve either of these when other methods are not appropriate or unavailable, and are often conducted in conjunction with other treatments.
The use of interferential therapy in terms of the muscular system is normally to aid in the treatment of spasms and strains, although use is limited in the event of infections or wounding to the region.
Interferential Therapy (IFT) at Dr. Ketan Bhatikar’s SPARC