IFC is a type of electrotherapy where two medium frequency current are caused to interact in the tissues to produce a low frequency effect. May be considered as a type of T.E.N.S. Maximal stimulation occurs at the surface near the electrodes, and decreases with increased depths. The sensory stimulation associated with low frequency currents is due to the high electrical impedance / resistance of the skin. Skin impedance is inversely proportional to the frequency of the current. Thus, high frequencies (> 1 000 000 Hz) have little sensory effect, low frequency currents (1 000-10 000 Hz) produce minimal sensory stimulus, thus, higher intensity of current can be applied to the tissues.

IFC is a phenomenon, which occurs when two or more oscillations are applied simultaneously to the same point or series of points in a medium. In simple terms, interferential therapy is a type of electrotherapy in which two medium frequency currents are caused to interact in the tissues to produce a low frequency effect. The first current is always of constant frequency, 4 000 Hz, while the frequency of the second is variable between 4 000 – 4 100 Hz, the difference between the two currents being O – 100 Hz.  At the point of crossover (point of interference) of two medium frequency currents in a tissue, a biologically active low frequency current is produced.  This is regarded as the most important effect of IFC therapy and several mechanisms for obtaining analgesia, which are frequency dependent, have been proposed.

These are:

• Impulse at a very short duration stimulate large diameter A beta nerve fibres:

Stimulation of these fibres has a modulating effect by closing the physiological “gate,, to nociceptive impulses carried in A-delta and C fibres.

• Stimulation of nociceptive fibres:

IFC can stimulate the nociceptive fibres directly. This causes impulses to pass to the brain stem region where the pain inhibitory system is activated. This results in impulse travelling in descending neurons to inhibit the activity of the nociceptor neurons at spinal level. This method of pain relief is likely to be obtained by using frequencies in the 10 – 25 Hz region.

• Physiological block:

It has been suggested that an interferential current applied with a frequency of above 50 Hz can cause temporary blocking of impulses in nociceptors.

• Increased circulation of blood:

Rhythmical muscle contraction brought about by IFC has a beneficial effect on local blood flow and tissue fluid exchange. This can relieve pain by removing the chemical irritants acting on the nociceptor endings, as well as reducing the pressure caused by local exudate.

• Muscle contraction

Beat frequencies in the lower range (0 – 50 Hz) stimulate motor nerves resulting in contraction of volant muscle. Autonomic nerves are also stimulated leading to contraction of smooth muscles in blood vessel walls. Rhythmical contraction obtained by varying the beat frequency exerts a pumping effect resulting in the benefit described earlier.

• Vasodilation

Can be obtained by applying IFC to areas where it will affect the ANS, e.g. the sympathetic ganglia. The usual frequency to obtain this effect is 100 Hz. It should be noted that beat frequencies  and

generally, should be avoided, particularly if there is a risk of thrombosis.

• Pain syndromes:

Neurogenic pain: Causalgia, post-herpetic, neuralgia and phantom limb pain. Musculoskeletal pain: Neck and lower back pain, (particularly when accompanied by appreciable muscle spasm), peri-arthritis, epicondylitis and fibromyalgia. Post-traumatic pain: Contusions, haematoma, chronic synovitis, tenosynovitis, ligamentous lesions, sprains and strains. Arthritic pain: Degenerative arthritis and rheumatoid arthritis. Autonomic pain: Associated with reflex sympathetic dystrophies (Sudeck’s atrophy) and Raynaud’ s syndrome.

• Circulatory disturbances

Acute and chronic oedema, atherosclerosis, diabetes, angiopathy Buerger disease, Raynaud’s disease.

• Miscellaneous conditions

Gynaecological problems, weakness of pelvic floor muscles, stress incontinence, constipation, migraine, asthma insomnia