Nilima, There are many misconceptions about interferential current (IC) which have been perpetuated by the manufacturers of this equipment over many years. The traditional theory that we have all been taught is that when we apply two slightly different medium frequency currents to the body, these somehow miraculously mix in the tissues and produce a new amplitude-modulated current that rhythmically increases and decreases in amplitude at a fixed and predictable frequency (the 'amplitude modulated frequency'). The actual evidence for this, however, has never been produced. Even in a homogenous water medium, the AMF is set up not just where the two currents mix, but also directly under the electrodes (Treffne 1983). Another study presented at the 1995 WCPT conference (Demmink 1995) found that, in tissue, the pattern of modulation was completely haphazard and unpredictable. The AMF, therefore, is unlikely to produce a predictable pattern within the tissues. Another misconception is that medium frequency current is incapable of stimulating excitable tissues but requires to be amplitude modulated at low frequency. At a frequency of 4,000Hz, each pulse of an evenly alternating current will have a phase duration of 125microsec and at 2,000Hz it will be 250microsec. These are well within the range capable of stimulating nerve and muscle. We have carried out work comparing pure 4,000Hz current (0Hz AMF) with a range of other AMFs and found that there was no clear difference in the effects that these settings had on excitable tissues (Palmer et al 1999). The medium frequency (4,000Hz in this instance) was therefore the dominant stimulating parameter and not the AMF (contrary to traditional theory). In fact no IC setting was shown to be superior to the stimulation possible with TENS (a much cheaper alternative of course). I agree that different AMFs do feel differently, and may also produce different patterns of muscle activation (tetanic responses at high frequency and twitch responses at low frequency). Amplitude modulation, however, is simply akin to turning the medium frequency current on and off very quickly (even though the pattern may be somewhat unpredictable). At frequencies above 40-50Hz, the current intensity becomes more constant and the body is no longer able to distinguish between separate 'pockets' of current. In terms of comfort, most individuals prefer higher AMFs (50-100Hz), but justification for different AMFs stimulating different tissues (as traditional theory would suggest) is difficult to sustain. Our work, and that of others, would suggest that IC is an inefficient method of stimulating tissues. TENS can probably achieve the same results more efficiently and at a fraction of the cost. There is more research being published in this area now, so views on the distinctive nature of IC as a treatment modality will hopefully change over time. Some references that you may want to chase up regarding the mechanisms of action of these currents (some in abstract form) include: ALON G. (1987) Interferential current news. Physical Therapy 67(2), pp.280-281. DEMMINK J.H. (1995) The effect of a biological conducting medium on the pattern of modulation and distribution in a two-circuit static interferential field. In: Proceedings of the 12th international conference of the world confederation for physical therapy, Washington D.C., pp.583. JOHNSON M.I. (1999) The mystique of interferential currents when used to manage pain. Physiotherapy 85(6), pp.294-297. KANTOR G., ALON G., HO H.S. (1994) The effects of selected stimulus waveforms on pulse and phase characteristics at sensory and motor thresholds. Physical Therapy 74(10), pp.951-962. MARTIN D.J., PALMER S.T. (1996) The effect of beat frequency on perceived comfort during stimulation of healthy subjects with interferential current. Physiotherapy 82(11), pp.639. PALMER S., MARTIN D., STEEDMAN W., RAVEY J. (1999) Interferential current and transcutaneous electrical nerve stimulation frequency: effects on nerve excitation. Archives of Physical Medicine & Rehabilitation 80, pp.1065-1071. PALMER S., MARTIN D. (2002) Chapter 18: Interferential current for pain control. In: Kitchen S (Editor) Electrotherapy: evidence-based practice 11th Edition. Edinburgh: Churchill Livingstone, pp.287-300. TREFFENE R.J. (1983) Interferential fields in a fluid medium. The Australian Journal of Physiotherapy 29(6), pp.209-216. I hope you find this information helpful. Kind regards, Shea Dr Shea Palmer, Lecturer & Joint List Owner, Department of Physiotherapy, Queen Margaret University College, EDINBURGH, EH6 8HF. Tel 0131-317-3356 Fax 0131-317-3815 e-mail mailto:[log in to unmask] ---------------------------------------------------------------------- Date: Thu, 18 Jul 2002 20:51:06 +0530 From: Shirish Bedekar <[log in to unmask]> Subject: Re: PHYSIO Digest - 16 Jul 2002 to 17 Jul 2002 (#2002-38) Hello members, writing after a long time. I am working as lecturer at Pune, India I teach part of electr- therapy. I have a doubt. If we say that laser energy is been given in pulses, still the wand/output gives a continuous red glow (wave length is in IR range, it is diode applicator.) Second doubt about Interferrential therapy. In theory we apply two medium frequency currents and interference is inside the tissues. It is still medium frequenct just under the electrodes. In practice we do experience the effect of Amplitude modulated frequency (low frequency effect) just under the electrodes also. How can this be explained? Does a frequency range of 2000 or 4000 Hz stimulate peripheral sensorimotor nerves? Thanks, Nilima Bedekar MScPT MCSP