When using a TENS machine for the first time, you come across a few unfamiliar terms and phrases. Listed below you will find a simple explanation.


The waveform of a current simply refers to its shape as seen on a graph of signal strength plotted against time.

Usually TENS waveforms are described as

symmetrical bi-phasic rectangular or

asymmetrical bi-phasic rectangular.

A bi-phasic waveform means that current flows in both directions. In the symmetrical bi-phasic rectangular wave the current is equal in magnitude and duration in both directions. This will result in both electrodes being the active electrode at equal alternate phases of the pulse. Equal sensation will come from both electrodes

By contrast, for an asymmetric wave, only one electrode will act as the active electrode. Sensation will predominantly come from the black lead connector.

Pulse Frequency

The frequency of a current refers to the number of pulses delivered per second; therefore a frequency of 200Hz means that 200 pulses are delivered per second.

Pulse Duration/Width

The unit of pulse duration is usually given in microseconds (µs) which are units of time, hence it is more correct to use the term ‘duration’ rather than ‘width’. The Pulse Width on T.E.N.S. devices usually range from 1-250uS. Generally speaking, the higher the pulse width, the more "aggressive" the stimulation feels.


Amplitude is also known as Intensity and is measured in Milliamps (mA).The amplitude is what you feel when you "turn the unit up". It's what causes the "buzzing" sensation of the T.E.N.S. to go higher or lower. The amplitude of a T.E.N.S. can range from approximately 0-150 mA. This is often set to patient comfort levels.