Unlike TENS, which delivers intermittent pulses to stimulate surface nerves and block the pain signal, IFT delivers a continuous stimulation deep into the affected tissue. The stimulation both blocks pain and reduces swelling and inflammation which can cause pain.
IFT achieves the deep penetration by using a 4000Hz carrier wave to overcome the skin impedance.
4 pole interferential works by putting two signals into the tissue at slightly different frequencies. Where they cross over, the two signals “interfere” to produce a lower frequency, therapeutic current. In theory, this interference current is generated in the pattern shown in the diagram. In practice, the tissues do not conduct uniformly, so the currents rarely interfere in the expected target area. Therapists commonly use moveable electrodes to “hunt” for the best electrode positions.
This is a real problem for unskilled home use. Many patients find just positioning and connecting up four electrodes a problem, without having to optimise the position.
Some expensive machines use vectored fields. These are a partial solution to this problem as they constantly move the interference zone around the volume between the electrodes, but this means that treatment is only delivered to the affected area for part of the treatment time.