I've ran and hiked for years; at my peak probably 30 miles a week plus long walks with the pup along with muay thai off and on and nary a problem. I thru hiked the Appalachain Trail last year (Northbound) and in the middle of Virginia it started to flare up - that familiar pain on the outside of my left knee. Always when going down hill, nothing going up. I wore thickly cushioned trail runners (Altra Olympus') the whole way, and have had a runner tell me too much cushion can cause "runners knee," but that could be a totally different thing. I've had lots of people suggest various stretching regimens, foam rolling, and various exercises but these are anecdotal sources at best. I've gotten so far post hike from inactivity. I think I could probably start jogging again now, but will probably try biking instead. Aside from this, do you guys and gals have any insight? I've been working on my stride and using more hip/glute which seems to maybe help?