Pred tapering seems to make my muscles more sore after a workout as well. It all depends how long its been since I tapered though. I taper 1 mg every 2 weeks and the first week I am fine. The 2nd week is when I feel the pain, especially after a hard workout. My GI said that is normal, it also makes any injuries I have flare up a bit. If you think about
it, exercise does break down your muscles each time you workout, so they can rebuild stronger. Your body has to rebuild them after each workout. Since, as somebody else mentioned, your body heals slower on Prednisone, it makes sense to me that it would take a little longer for your muscles to recover after a workout.
High doses of prednisone are another story, I felt like I could workout for hours then!