How does Interferential (IF) Work?

In the USA, Interferential Therapy is approved for the symptomatic relief and management of chronic (long-term) intractable pain, post traumatic and post surgical pain. Many medical professionals use Interferential Therapy for drug free, non-invasive promotion of healing and pain relief. It has been shown that multiple daily treatments give improved results. Home treatment can help reduce pain, medication, and oedema. Interferential Therapy can be used to treat pain associated with:

  • Back, Neck, Shoulder and Knee injuries or problems
  • Fibromyalgia
  • Joint injuries
  • Overuse injuries and surgical procedures
  • Oedema, Inflammation
  • Carpal Tunnel Syndrome
  • Tennis Elbow
  • Sports Injuries

How interferential works

Unlike TNS, which delivers intermittent pulses to stimulate surface nerves and block the pain signal, Interferential delivers a continuous stimulation deep into the affected tissue. The stimulation both blocks pain and reduces swelling and inflammation which can cause pain.

IF 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 therapeutical 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. In Bipolar mode, the Ultima IF4160 overcomes these problems. Early IF units used analog circuits, and were limited in the waveforms they could produce. Ultima IF4160 uses digital waveform generation to produce true sinusoidal bipolar IF. This uses a 4000 Hz carrier wave, but delivers an amplitude modulated low frequency signal to the whole area between the electrodes, not just the interference pattern.

Effects of Interference Frequencies

Physiotherapists believe that the low frequency interference currents have the following effects:

  • 2Hz Around this frequency the metencephalins are stimulated which will result in short term pain relief.
  • 10Hz This frequency has a beneficial effect on the immune system and tends to make patients wakeful yet relaxed.
  • 130Hz This frequency stimulates the production of endorphins and results in longer term pain relief and some local anaesthesia.
  • 1-100Hz This frequency sweep will increase the inflammatory rate.
  • 45-90Hz This frequency sweep will depress the sympathetic nervous system so allowing increased activity of the parasympathetic system, and increase the blood supply.

Interferential Therapy as part of a treatment regime

To derive the most benefit from interferential therapy it is as well to appreciate a few points about its and your respective roles. The use of IFT should be considered a part of the whole treatment of the condition. The whole treatment may include:

  • Exercises to stretch injured muscles
  • Exercises to move stiff joints
  • Exercises to strengthen muscle groups to support the joints

Your physiotherapist will advise you accordingly.

Stiff joints are invariably painful so it is important to appreciate that gentle movement is generally better than resting. A TENS unit, which also treats pain using electrotherapy but in a different way, can be used simultaneously if you need extra pain control to enable you to keep the joints or muscles moving.

Cautions and Warnings

The same cautions apply to IFT as to TENS. However, because of the deep penetration of the signal, additional caution should be taken not to place electrodes so that the current could flow through the heart: The maximum current density is below the level recommended safe levels which might affect heart rhythm, but it is best to prevent even the smallest avoidable risk.