My first time on prednisone, I was on it for 7 months. It took about
a month for my flare to calm down a bit and I just couldn't get off of the prednisone. I gained 24 pounds but tried to continue my exercise program as much as possible.
I am on prednisone for the second time now, going on just over two months, and am tapering off now. Only one more week! This time around, I didn't gain any weight and I felt better within about two weeks or so after starting it.
I am sure it is different for everyone, just like which drugs work or don't work, what foods upset our systems, and severity of symptoms. For me, the fatigue is my biggest obstacle to exercise not the weight gain. And for me, I had to decide, what is more important, feeling better or working out? Easy decision.
Good luck.