It's a good question. I think in my case, the scalene stretches cause the first rib (to which they connect) to elevate, which then pinches the nerves and blood vessels that lay over them.

I've also wondered if people could have adhesions between their brachial plexus and their scalenes such that stretching those muscles would pull on the plexus and irritate it.

Whatever the reason, I know from experience that neck stretching makes me worse. Which is very unfortunate as it works great for the rest of my body (pec minor, back, hips).

Someone just posted that they found scalene stretches to be very helpful to them. So maybe the real advice should be to try them out at some point and see which category you fall into.

Additionally, I have to try things one at a time because otherwise it can be hard to distinguish what's helping and what's hurting.

I would also add to the list:

* Monitor posture using the iPosture device.