My dad uses a TENS for his back pain, had it for yrs now.

I have had PT & chiro use another type of electrical stimulation called IF stim.
It is great for muscle type pain, it goes deeper than a TENS and without the stinging if turned up.

I bought a EMS {electric muscle stim} for my own home use but I sometimes wish I had gotten the IF {needs a drs rx/sig to buy}

this tells of the differences-
http://vitalityweb.com/backstore/Muscle-Stimulator.htm