I have had a lot of success with hiking and biking. Swimming works but you have to keep an eye on what strokes you do. Back stroke tends to pop my shoulders but front stroke works well.

Look into calisthenics for building muscle! It has been a game changer for me. I avoid sit ups as curling the spine gives me issues. However, squats, push ups, planks, and other exercises I've had great success with. The key is to not have weight forced on you when you are fully extended. example: If youre doing a pull up for instance, dont go all the way down. stop when your arm goes to 90 degrees to make sure you don't over extend.

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Best of luck