Ahh, but here is the good news - you need not stop all resistance and strength training due to a shoulder injury! The PT can show you many safe exercises to do. Also, there are shoulder-sparing positions for doing planks. I cannot due a standard plank due to arthritis in hands, elbows and shoulders, but can do modified versions on my forearms. And resistance doesn't always mean machines at the gym. We use a variety of resistance bands and even our body weight to exercise because we travel, and finding a good gym isn't always possible.
Sue