Interferential Current Therapy (IFC) is a variation of transcutaneous electrical nerve stimulation therapy delivered by a TENS unit.
It uses medium frequency electrical signals instead of the low frequency ones used by traditional electrical nerve stimulation. Further, it does this in a manner designed to reduce the discomfort sometimes experienced by recipients of traditional TENS therapy.
TENS therapy aims to electrically stimulate the nerves just below the skin. It controls the pain experienced by individuals suffering from conditions such as arthritis, low back pain and other medical problems. The traditional form of TENS therapy uses low frequency electrical signals for this purpose.
However, these signals need to penetrate the skin to reach the nerves underneath. The impedance of skin tissues is however inversely proportional to the frequency of the electrical signals attempting to penetrate them.
This means that the low frequency electrical signals encounter higher impedance than if medium or higher frequency signals were used. This results in higher patient discomfort.
This higher impedance manifests itself as greater patient discomfort. It tends to negate the pain relief effects of the therapy and can potentially lead to lower patient compliance.
How Does Interferential Current Therapy Work?
As we have mentioned, there is an inversely proportional relationship of electrical signal frequency to skin impedance. Lower frequency signals experience higher impedance and cause more discomfort.
However, this also means that increasing signal frequency allows the electrical signal to pass more easily through skin tissues. The result is less skin discomfort for the patient.
However, there is not much evidence of the effectiveness of medium frequency signals where nerve stimulation and pain relief are concerned..
Interferential Current Therapy combines two medium frequency signals that will pass more easily through the skin. This is due to these signals requiring less energy to penetrate the skin.
The medium frequency signals are combined in a way that causes them to partially “offset” each other.
As a result of this “offsetting”, these signals can “mimic” the effects of low frequency signals. They simulate the signals used in traditional electrical nerve stimulation.
Patients can therefore get the “best of both worlds”, i.e. pain relief from effective nerve stimulation together with less skin discomfort.
Many IFC units also allow the user to vary the input frequencies. This may be done in order to control the resultant frequency of the combined signal. As a result, doctors can alter the tradeoff between patient discomfort and the effectiveness of the nerve stimulation.
They can also use this capability to increase therapy effectiveness using frequency sweeps. We elaborate on this in the next section.
IFC With Frequency Sweep
An interesting variation of IFC therapy with a constant frequency is therapy that uses a continually changing signal frequency. This is done to overcome the ability of nerve tissue to adapt to a constant frequency. This adaptation means that the ability of a signal with constant frequency to stimulate the nerves decreases over time.
As a result, continuously varying (or “sweeping”) the frequency of the output signal over a treatment session can improve therapeutical results. Different sweep patterns are ultilized by different units and the effectiveness of alternative patterns is under study.
Can IFC Be Used For Other Purposes Besides Pain Relief?
Because of its versatility in producing a range of signal frequencies, IFC has many applications in physical therapy. As we have mentioned, it can be used to relieve pain.
However, it can also be used as a muscle stimulator. Athletes undergoing rehabilitation from injuries that have caused muscle deterioration through disuse can use it for muscle toning. This type of application is discussed in greater detail in our electrical muscle stimulation category.
Therapists also use IFC for the following clinical applications:
Increasing local blood flow near the site of injured soft tissues; and