On PMR again and started Prednisone a 2 weeks ago.

I have been using my Apple Watch to track my fitness and in various
categories for a year and I found my Cardio Fitness VO2 Max value going down since being diagnosed with PMR. I have been increasing my walking both distance and difficulty and still my fitness numbers continue to go down. Is it possible that Prednisone usage impacts fitness level? . I am on 20 mg Prednisone