This is the official definition:A TENS unit is a pocket size, portable, battery-operated device that sends electrical impulses to certain parts of the body to block pain signals.The electrical currents produced are mild, but can prevent pain messages from being transmitted to the brain and may raise the level of endorphins (natural pain killers produced by the brain).
Electrodes are attached to the surface of the skin over or near the area where you are experiencing pain. It is important that you learn how to:
correctly put on the electrodes (proper placement is important)
operate the unit
change the batteries
vary the controls and settings (both the frequency and voltage)
set the proper duration and intensity of the stimulation (which depends on the location and type of pain)
TENS units are prescribed for both acute pain and chronic pain conditions such as:
For some chronic pain patients, a TENS unit provides pain relief that can last for several hours. Some people hook the unit onto a belt turning it on and off as needed.
When I use mine, I use 4 electrodes placed in a diamond formation as shown in the thread Jamie gave you. The machine has a variety of modes of impulse, some like trickling, others like pulses, there is one like tapping. The idea is that you try each one and see which suits you, which you feel most comfortable with. There is usually one setting which is a medley of most of the other settings which is the one I mostly use. The point being that eventually your nerves get accustomed to one mode so have a series of modes in the one setting means the effectiveness lasts an awful lot longer.
You can also choose a strength of signal. Start off with a fairly mild setting and in the first couple of minutes raise it until it reaches a strength that you feel comfortable with. At first you will be very aware of it but gradually, it will seem to fade. This is the point where it has reached peak efficiency and the area has become a little numb. Resist the temptation to turn it up as it will not increase the overall effectiveness and if it goes up too high, you could even risk a small burn under the electrode. Most units also have a timer so it only runs for 30 minutes which is reckoned to be the safe amount of time though I frequently turn it on again many times one after the other. The timer is good to have if you should nod off to sleep with it on!
I do put my unit in a pocket or something and get on with things, even going for a walk. When I had my arthroscopy in 2006, I used it to get to work and wore it for the whole shift! I kept the unit in my scrubs pocket so I could switch it on and off. Mostly I had it on until I had a patient come in and then I switched it off so as not to have a distraction whilst looking after someone.
Things you should not do with the unit on is drive, bath or sleep!
Regarding other pain meds, it all depends upon the degree of pain you have. I've used it on my lower back, upper back (never the neck) shoulders and knees. It's not good to use on the areas with less 'coverage' like forearms, hands, ankles and feet as it needs a degree of thicker tissue to help conduct the impulses. So I would use it either instead of or as an adjunct to oral pain meds. It really doesn't matter. Your choice entirely.
Oh yes, and it doesn't help healing as such. But it will help with that stiff, sore knee. It will just make you more comfortable over all. I've always loved my TENS, it enabled me to get back to work in 06 and lots of other things!