First day of PT was interesting. The PT confirmed my belief that I have tendinosis, not tendinitis ("tendinitis doesn't last this long").
Based on the objective/subjective observations, he also believes there is a partial tear in one of the rotator cuff muscles.
I did several different exercises, some of which I am to do at home on days when I don't go to PT. This morning, my triceps hurt more than the last time I did an upper-body work-out at the gym (2 months ago).
I was asked to do a modified sideways plank (on my knees rather than my feet). I couldn't do that for even a second without a lot of pain (2 months ago I could do that for at least 1 minute on each side, pain-free). The PT was very surprised (I wasn't), then said "We have a lot of work to do...". If he thought I should be able to do that, and then was surprised when I couldn't, I wonder if there's something else going on or if things are worse than they suspect.