I've had lumbar stenosis and thin discs for what seems like the better part of forever. Also shoulder pain. As usual, I experimented on myself to see what might work as the physical therapist thing was a total bust. I agree that cycling is the best thing for back pain. I couldn't ride for a while due to a severe saddle sore and my back got really bad and turned into sciatica. So I had that to deal with. Anyway, not being prescriptive for obvious reasons, but this worked for me:
Shoulder pain: As was mentioned above, we didn't evolve to carry heavy weights in our hands. We did however hang from our hands. Remember how much fun monkey bars were as a kid? There's a reason for that - we're supposed to hang. So I hung from my hands for 2 X 1' several times a week, that's all. Fixed it. Took a couple months or so, used one of those doorway chin bars or at the gym.
Lower back: I walked a lot, 2-3 miles most days while rolling each hip in an exaggerated circular motion - that's important. Not quite sure what that did, but it fixed me right up. Hurt like the very devil when I started doing it, but only for the first mile, then the pain went away. That's a sign you're doing the right thing. After I could walk pain-free, I got back in the gym doing ATG squats, first no weight, then barbell squats, 3 sets of 12, as much weight as I could handle on the last set. Also stiff-legged deadlifts, same. Also back machine but not with max weight, just lots. Unsupported seated dumbbell presses. Lat pulldowns. Seated rows, I never did crunches, don't think they're a good idea. I did back work. Sure, my back still hurts a lot. Doing dishes is maybe the worst. Any sort of standing for long periods, so I do too much sitting, like this. Bummer, but what can one do? I plank now. Morning stretches, then pushups, then plank and side plank. I can ride however far, no back pain.
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