The way I understand them is they use the Gate Control Theory for pain relief. With enough non-painful stimulation to the nerve fibers the "gate" closes preventing the pain impulse from reaching the central nervous system. The theory has been around since the mid sixties and it seems to work. Whenever I give an IM shot I will spend about 10 seconds or so producing pressure over the injection site with my finger before I stick the needle in. Through giving many, many shots and anecdotal evidence such as "wow, I didn't feel that" or other things like that I believe it *may* work. Of course that is only for the needle stick, it wears off quickly and the pain from introducing a foreign substance into the muscle may still cause discomfort. Although the TENS unit is now becoming available to the masses, for years it has been available as a prescription device as an adjunct to various other pain control methods.
bob
