One thing I switched while pressure flaking is holding the flaker with my whole fist. For a long time I was using my pointer finger pressing on the flaker and I see a lot of that with newer people. There is less power and it hurt my joints.
Last couple months I've been thinking about my posture, etc. Concentrating on sitting up more, keeping my head up, etc. Not doing the cave man hunch. I've been standing up every few minutes to relieve my lower back, which used to get real tight, that was the worst for me. But, I've started a stretching (yoga) regiment and it's gone.
I don't get leg pain from percussion but most of my percussion is freehand.