This is a widely misunderstood concept. Electrical resistance of an electrical element (i.e., an electrode) measures its opposition to the passage of an electric current. Electrical resistance is measured in OHMS (Ω).
The electrode industry routinely uses the term impedance, which is an AC current-specific term. Below we clarify the two terms:
Electrical resistance in a DC current is resistance.
Electrical resistance in an AC current is impedance.
Since electrical stimulators (TENS, IF, NMES, HVG micro current, etc.) can have either an AC or DC current, the use of the term impedance is incorrect. However, the term electrical resistance can apply to both types of currents and all types of stimulators and is therefore a preferred term.
Electrical resistance can be an important measurement, but a better measurement of an electrode's performance is electrical conductivity. Electrical conductivity refers to how much electricity is being conveyed from the stimulation device to the patient's skin.
We have seen many flawed methods of measuring impedance, varying in accuracy of measurement equipment, methods of obtaining the measurement, incorrect equipment settings, and such. Additionally, some electrode manufacturers only test the electrical resistance of the naked dispersion pad (carbon, silver, etc.) and quote those results without consideration of the effect on electrical resistance from the lead wire connector (pin connector), the lead wire itself, or even the hydrogel. In short, impedance or electrical resistance measurements from most electrode manufacturers are not reliable factors for comparison.
Conversely, using the H.E.C.A.T. (Hydrogel Electrode Comparison & Analysis Tool), the entire electrode can be tested � dispersion pad, connector, lead wires, and hydrogel. There are 324 electrical resistance test points for a 2"X2" electrode and in seconds, the H.E.C.A.T. takes thousands of measurements. The H.E.C.A.T. can also test electrical resistance on AC and DC currents. Its measurements are wholly reliable and represent the electrical resistance of the entire electrode.