noname- if on a treadmill you are resting your arms on the rail and if outside yuo are dangling/swinging youre arms, that is probably enough of a difference right there.
I do think that for some, if you can engage your shoulder blades before swinging your arms (so your are sort of pulling your shoulders up and back a bit rather than letting them hang loose) it will reduce the trendency to swell.
One of the PT's i stopped seeing for other reasons gave me that shoulder blade advice the first day i saw him (it was enough to get me to come back, but he proved not to be very sensitive to us painned types and I eventually left him a few flares later) . He proved it by lifting up on my elbow while i tried to look side to side, and without the shoulders pulling down i could move farther. He said it was because my traps were overstretched (as opposed to too tight which is what i had thought they were).
I am not sure this explanation is correct, but it does help the pain in my arms when I walk or lift things or do exercises if i engage the shoulders first-
so there you have it
As for ultrasounds, well, Dr Jordan does an ultrasound and sees almost the same thing as Dr Collins 12,000 MRI/MRA but the ultrasound costs $390. Generally they are simple and painless- i don't know how you could go too wrong.
GOod luck, adn you are probably right to investigate the source of the sweilling- some can be a sign of very bad things, other i think is more just annoying.
Johanna