Is tread milling, simple stretching, or yoga ok to do while running contact?

It is fine, the biggest issue for most will be the sticky contact pads. they lose their stick while doing everything. This is coming from wearing a tens unit a lot for years. the old pads had gel you used and you could wear them in the shower, but the new ones, like we use now are the removable and reusable ones which if you sweat much come off. or come off part way which cause the electricity to sting a bit. I would not use on my legs proper though while continuously walking, the leg muscles are working and I would not want to interfere, just stick'em a little higher. I remember walking hours with the tens pads on my lower back near l5-s1 and have the thing turned up so much as to almost cripple me, and still motivate just fine. Of course I have not had the spooky contacts on while tread milling, as even if I used this beast of a treadmill in my living room (which I should) I would run the phanotron... but really, you will be fine. so nope, no excuse to not do it now Larry.

For more details, please check:
https://www.spooky2.com/forums/viewtopic.php?f=23&t=9717