I have used Tens in the past for sciatica and general back pain though not since I have had bladder cancer. It helps control pain by vibrating the area the pads are attached to - there's a central unit which generates the vibrations - strength and type - and a number of adhesive pads you place on the skin above the painful area. They also use it during childbirth (I think).
What I think happens with Tens is that tense muscles cause pain and the vibrations make them relax. As it is non-invasive it might be worth trying, especially if it helps you notice what is tense so you can try to relax them yourself at other times.
I have managed to do that so haven't needed the Tens for a long time, despite my spine having deteriorated since.
My favourite way to relax pelvic muscles would be to lie on the floor, knees pointing up and legs in a reverse V, head on a book so nose points up, arms on floor, hands gently on front of hips and breathe slowly and deeply, noticing tense areas and telling them to relax. (It's called the semi-supine position.)
One of the worst areas for clenching when in pain elsewhere is the jaw, especially as that seems to act as a signal to lots of other muscles to tense up. That plus a hot water bottle might also help for bladder spasms though I have never tried.
Many thanks for the detailed reply. I've also looked up on the company website (Auvon) and they advise avoiding near tumours and trauma sites. I've just finished first six BCGs and was planning to use on left shoulder and lower back, but given side effects from BCG, might just keep it to the ankle and knee.
Thanks for your message. Sorry, I should have put it in tge query, The TENs unit is an electrical muscle stimulator for pain management which I am hoping to use on lower back and shoulder pain. I'm looking know house only on ankle and knee for the moment while the BCG side effects settle down.
Maybe the lying down might help on its own? Every time I do it the lower back stretches itself out - I wriggle around to give it more room- and that gives space between the vertebrae and reduces the pain. Same with the shoulder, it can drop back into place too - gravity is helpful in those spots
