As a runner and PT, PFPS (or patellofemoral pain, as it’s now referred to) is a pretty substantial part of my life. It’s the most common running-related injury in most populations and very much follows the “too much too soon after too little for too long” pattern. The envelope of function post that I dropped in the ITBS thread was actually developed after a surgeon had his partner perform an arthroscopy with only local anesthesia on his knee and poked around to make a neuro-sensory map; basically, he was awake for someone to poke around his knee so they could figure out what structures hurt the most. PFPS used to be known as “chondromalacea patella” and after this landmark study, we don’t really see that anymore. That’s because the cartilage under the patella isn’t what hurts- it’s the highly innervated tissue under the kneecap that doesn’t seem to get damaged in cases of PFP, it just gets sensitized. Sounding like a broken record, the patellofemoral joint just needs to improve its tolerance to loading; from a total amount of force passing through the joint to plyometric/speed-based loading. This can be a relatively chronic or weak point for some runners, but I always recommend some adjunct quad strengthening. Hip strengthening in conjunction with quadriceps strengthening seems to be part of a comprehensive program, but most rehab should take the lowest hanging fruit of addressing quad strength deficits before anything else unless it’s too painful to do that.