Are electro-muscle stimulator effective for low back pain?

Sometimes: I have had pros and cons. Some folks feel that it increases their pain. Muscle stimulators are really nerve/muscle stimulators and have a multitude of chemical effects upon the nerve and the muscle which can promote healing and improve pain. You really are not going to 'hurt" anything by giving it a try.

Maybe: There is no data to support this modality in low back pain, that doesn't mean that it doesn't work. Some people may respond to it.

TENS: TENS (transcutaneous electrical nerve stimulation) machine may help depending on your pain issue. Usually they can help acutely and if you get long term benefit great, they are just masking the pain while your body heals. If you continue with pain or not getting relief with TENS then consider eval with a pain/spine specialist.