I don't think this is technically an injury (yet) but I want to do anything I can to avoid getting there!
I've been noticing a tightness/stiffness/pain? in my shoulders. This has been most noticeable in yoga class, but I also feel it during strength training (especially cuban snatch or the "L" in YWTL). I'll post some comparison photos in a sec, but first a description of the pain, last night as an example:
During an extended forearm sequence during class I felt intense achy, uncomfortable, unable to hold one of these pose more than a few seconds. Now, the following morning, I feel more moderate aching and a strange warmth in my shoulders as well as my wrists and elbows (during class I felt it in shoulders only). Oh and I'm not sure if this is related, but I've always been one of those people who responds to stress by pushing my shoulders up around my ears, and I sit at a computer most days.
I'm wondering if there are pre-hab exercises, or stretches or something else I should be doing to improve this. (or should I just avoid doing these poses?).
For example, I can do this with no pain or discomfort:

but this is very challenging (ignore the leg in the air, it is the arm/shoulder position that is the problem):

similarly, I can't even get into this position:

but this is ok:

finally, this pose has been an issue that we (my teacher and I) think might be related. I can get into the position and hold it, but I can't come out of it smoothly--basically I come down and inch or two then flop hard onto the ground:

Ok, sorry for the novel length post, but maybe someone has some ideas for me? Thanks!