How about a brisk walk? I know its not the same, but about 1 hour of brisk walking burns a bit less than 30 mins of running. You will still have some impact on your muscles (not as much as running, but better than nothing), but you won’t be running the risk of hurting yourself! If your desperate, try getting those weights you can attach to your ankles for a bit more resistance, and walking with a friend is loads of fun because you can have a chat without losing your breath haha. I know its not a hardcore gym sesh, but because we slow down activity so much after surgery, we need to take it easy getting back into it anyways. They say going back to the gym should be like a beginner again, so I think two weeks of brisk walking will be the perfect thing to get you back into it! Sorry if that’s not much help, but its what my mum recommended to me (she’s an expert when it comes to nutrition/bodybuilding/workouts) xx