“and as a result, they don't swell up (edema?) in the afternoon, like they did before I started using them.”

Yea, I also noticed poles stop the hand swelling. I can get hand swelling on long walks w/ or w/o a pack. But when I started using my GG strapless poles 5+ years ago, I noticed my hand swelling was totally eliminated.

In fact, if I ever go walking w/o poles and my hands just start to swell, I put my hands into fists (as if holding a pole) and squeeze/pulse them to my walking cadence. And then the swelling never comes. I didn’t know about this trick until I got my GG poles. So I can relate to your “periodically squeeze and release an imaginary ball”

It’s just another bonus of poles.
-Barry