I have flat feet since I was a child. I’ve worn orthotics since age 35, and I am 50 now. In Nov., 2003, I had new orthotics made and switched to only SAS shoes for daily wear. My feet are happier, but I still find it hard to do any regular exercise because of discomfort under my metatarsals and sometimes, the inner aspect of both ankles. My feet don’t tolerate walking on hard surfaces. Would using a nordic trac ski machine beneficial or harmful for bad feet?