Summary
Highlights
Interferential currents are medium-frequency currents that superimpose to create a characteristic interference pattern. Frequencies from 0 to 2000 Hz have high excitability, 2500 to 5000 Hz show diminished excitability, and above 5000 Hz (high frequency) have very low excitability, primarily affecting nerve endings rather than muscle contraction.
Lower frequency currents (below 2000 Hz) cause more resistance in the skin, leading to uncomfortable sensations like paresthesia (tingling, pricking). Higher frequencies reduce skin resistance, making the application less bothersome. Currents around 4000 Hz have less resistance, similar sensations to galvanic currents, and produce electrostimulation. 2500 Hz currents are the most stimulating, while 4000 Hz currents are more for analgesia.
Impedance is resistance. Increasing frequency decreases impedance, especially in the skin, improving current conduction. This allows for higher intensities without uncomfortable sensations, as the reduced impedance eliminates paresthesias.
Interferential currents are generated by superimposing a carrier frequency and a variable frequency. The superposition creates an interference pattern with variable intensity. The resulting cyclical current has a much lower frequency, which is the difference between the carrier and variable frequencies. This difference creates the Amplitude Modulated Frequency (AMF), showing the sinusoidal interference pattern. This occurs in the area where two circuits (e.g., A and B with electrodes) overlap.
The superposition of medium-frequency currents aims to apply significant intensities to the patient without the discomfort of low-frequency currents. This is achieved by decreasing tissue impedance and minimizing sensory and motor effects in unwanted areas.
Besides the common sinusoidal pattern, there's a quadrangular modulation (also known as Russian or Kotz currents), used for muscle strengthening by forming 'trains' of impulses. There's also triangular amplitude modulation, specifically for peripheral denervations. However, in Argentina, exponential current is typically used for denervation, so the triangular pattern is not commonly employed.