How to set a TENS unit?

The settings of a TENS unit such as the TENS 3000 or the TENS 7000 depend on the method with which you want to relieve pain. If you want the electrical impulses to disrupt the transmission of pain signals from the nerves to the brain (known as the gate control theory of pain) you have to use a high frequency; if you want your body to release naturally-produced opioids called endorphins (known as the endogenous pain control system) you have to use a low frequency. By frequency we refer to the pulse rate and pulse duration (width) settings of your TENS device, on Normal or Continuous mode. 
A typical high frequency setting would be a pulse rate of 80 pulses per second (pps), and a pulse duration or width of 60 microseconds (μs). This type of setting provides a soothing ‘buzzing’ sensation that obstructs the emission of pain signals to the brain. In some instances the pain may be checked anywhere from 30 to 60 minutes after a session; in such a case you may want to reapply after 90 minutes in order to enhance the results. Often, however, the unit must be worn constantly to prevent the return of pain. Settings may vary for more serious pain, for example 80 pps pulse rate and 150 μs pulse duration.

Low frequency, on the other hand, requires different settings, like 2 pps pulse rate and 200 μs pulse width, for example. This will produce a massaging sensation that releases endorphins rather than the buzzing feeling associated with high frequency. The effect of low frequency TENS may last up to several hours in some cases-which means that the unit it doesn’t have to be worn continually-as long as it’s applied for more than 30 minutes with a pulse rate below 4 pps. People who must constantly wear the TENS unit even in low frequency would be better off switching to high frequency.
If your TENS unit has Burst or Modulate mode-or both-, a good starting point would be a pulse rate of 100 pps and a pulse duration of 100 μs; some users have experience an increased calming effect with these settings in Modulated mode. The above-mentioned high frequency settings may be tried with either burst or modulated mode, if you feel so inclined. In low frequency, though, their effect on pain will be negligible.

Related Read: What are the recommended settings for a Tens 3000?