When I go to Kodiak to fish for silvers every so often, I cast from shore to "targets" (i.e., jumping or finning fish). On a typical day, I will start about 7:30 AM and fish until dusk. I can go a day or two without shoulder pain, but after that, the constant slinging of heavy line over a long period of time practically cripples me. I attribute the pain to poor mechanics, but I'm so far into my dotage I'm not about to learn new techniques -- so, pain killers. OTC stuff works OK.
When fishing from a float tube, I don't have the right shoulder bending-over-and-hope-it-goes-away pain, but, I;d rather fish from my feet when I can, even under these conditions.
For what it's worth