When you do your backrub, what I do and you may do it too. I used to be the same, feel tortured while you do it and your that close but can't even do your thing...
The way I do my backrubs and leg rubs and stuff today, is enjoy the physical contact. I also enjoy if she is taking pleasure in it. I think you will enjoy it too if you have the right state of mind going into it.
I also see how asking for it or mentioning can get the spouse defensive. The defensive action indicates they are obviously ignoring it, somehow its a pain point. Why would they avoid this talk if they know their spouse needs aren't met? Don't they realize it?