This is sounding similar to the way my PN is progressing. I've been doing 4 to 6 miles a day either trail hiking or walk-jog-walk on streets -- but lately my leg muscles feel rubbery and stiff, and hurt sometimes. My knees hurt like heck sometimes, though icing after the workout helps a lot. It's not "overdoing it" because I've been working out like this for a long time, and the hurt is new.

I'm going to a new doc next week, with a list of questions on exercise and muscle wasting -- I'll share anything useful.