interferential current
/ in-ter-FEER-en-shul /
Ordinary TENS uses a low-frequency current, which the skin resists and which can feel prickly when you try to reach deeper tissue. Interferential current is a clever trick to get a comfortable, deeper-feeling stimulation: it uses two medium-frequency currents that cross inside the body and 'interfere' with each other.
Two pairs of electrodes are placed so their currents cross over the painful area. Each current alone is a medium frequency that the skin lets through comfortably, but where the two currents meet they combine into a new, lower-frequency beat — much like two slightly out-of-tune musical notes producing a slow throb you can hear. That beat frequency is the part that actually stimulates the nerves for pain relief, but because it is created deep inside where the currents cross, the patient gets the therapeutic low-frequency effect without the uncomfortable skin sensation of applying a low frequency directly.
Interferential current is used for much the same goals as TENS — easing pain and sometimes reducing muscle spasm — and is popular partly because it is more comfortable than plain TENS for deeper or larger areas. Its honest evidence, however, is much like TENS: relief is often real but modest and short-term, and it works best as one comfort tool inside a programme led by exercise. It shares the usual electrotherapy precautions: avoided over the heart and pacemakers, the front of the neck, numb skin, and a pregnant abdomen.
To ease a patient's deep low back ache more comfortably than plain TENS would, the therapist places four electrodes so two medium-frequency currents cross over the spine, creating a soothing deep beat where they meet.
Two crossing currents create a comfortable deep beat where they meet.
Interferential current is often more comfortable than TENS, but its proven benefit is just as modest and short-lived — comfort is not the same as superior effect.