I got a "tens" unit from a chiropractor friend. I wanted to stimulate my calf muscles to improve circulation in my foot where I have two unhealed wounds.
At ~60% power, it would seriously trigger my arm muscles but it had NO effect on legs at 100% Similar units sell for less than $50.
I posted here somewhere and spinal nurse replied that these types of stimulators will not cause contractions if you have a spinal injury, that somehow the nerves, despite being secondary nerves and not spinal, die.
The stimulators that were possibilities were many hundred dollars.