I hear you. The first rule is: "don't injure yourself". On feet: try out "Superfeet" insoles (not affiliated). I recently learnt about 'em and been trying for a month; they're working well for me. I have a flat left-foot, and it starts paining after 18K. And I limp a little bit for a day with pain, and it goes away. I hate this, and have lived with it for too long. Finally, I began with a specialist (podiatrist) to see if I can find a long-term fix.