Right – see a Doc, get diagnosed. Thanks.
First I'd like to do some strengthening. Experience with the rest of my body indicates that, in general, some muscle groups are not playing well with others.
I don't have any range-of-motion restrictions, only sharp pain with some moves – like closing the hatch on the van, or reaching across my body to pick up my pack, or cleaning the stove-top. Not every time, but often enough to get my attention. It may be related to the casting motions associated with fishing – fatigue after a long day on the river. Using trekking poles does not seem to exacerbate things.
I have Thera-Bands and free weights.
Got a recommended set of exercises, or favorite YouTube videos for a general "tune-up"?
Know any exercises I should Not do? (Aside from the ones that hurt.)
Thanks.

