Originally Posted by Elihawk
Ex runner myself, after about 6 marathons and 20 years of running, an orthopedic Dr warned that I was fast tracking a knee replacement if I didn't stop.
FWIW, I would have gotten a second opinion on whatever was ailing you. Unless they run themselves, most doctors are just going by whatever fear-mongering outdated crap they got spoonfed in med school (podiatrists are especially useless for runners).
People usually get injured due to 3 things:
1. Training errors: increasing mileage too suddenly/much, insufficient recovery time, etc.
2. Poor biomechanics: overstriding and landing hard on the heels, often encouraged by many mass market running shoes with huge thick heels and inflexible soles. Treatment = working on correct form, esp. by running barefoot or in minimalist shoes at least part of the time. "Stability" and "motion control" shoes are the worst, closely followed by orthotics.
3. Core muscle imbalances: weak abs, lower back, or glute muscles that become tight/stiff as a result, causing biomechanical dysfunctions. Treatment = running specific core strengthening exercises and myofascial self release (e.g. foam rolling).
Knee pain is often a symptom of problems elsewhere, not in the knees themselves unless you are doing some kind of crazy pro-runner level training like running +100 miles per week. The typical person's 20-40 miles per week shouldn't cause any knee problems, in fact runners have been found to have STRONGER knees than most folks.