In reply to CragRat11:
Modifying training is great, but I'd start with your feet, right shoes and inner soles, then work up. Many lower leg or knee problems can be caused by problems lower down. I did a lot of mileage right through my youth, then even more in the hills in 20s, 30s, 40s, always thinking that my sore feet on that last km of tarmac were down to the previous 30. Turns out I have poor arch and mid foot support, causing metatarsalagia, semi bespoke inners and it's a revelation. Plus some extra exercise on top. Prior to this my weird feet were triggering calve problems because the connecting tendons literally run right down the side of your ankle and under the side your foot.
I'd visit a podiatrist and or sports physio, check your gait, foot plant, where your feet apply pressure etc.
For general muscle strength training you can't go far wrong with gauntlet stairmaster machines. No pounding tarmac running, etc.. and they'll strength all those legs muscles around your joints. Plus balance exercises for ankle strength.
Post edited at 11:39