When I was younger, I once had a check-up with my doctor where he asked me if I was a little league catcher.  At the time, I wasn’t, but I was idolizing Los Angeles Dodgers catcher Mike Piazza so I took it as quite the compliment.  Then my doctor explained that all the cartilage in my knees was torn up as if I kneeled down all the time.  I had no explanation for it.  I never kneeled down or, at least, I couldn’t remember ever kneeling down for anything.  I sat down a lot, especially when in school, but also to watch TV and play video games.  The doctor said he didn’t know where all that torn cartilage came from either, but he showed this leg stretching exercise to do a few times every single day and suggested that I start drinking more orange juice or anything with vitamin C in it.  Diligently, I did all he suggested, at least for a little while.  I was a little kid after all.  I didn’t have the discipline to keep up with everything.  But at the next check-up, the doctor didn’t say anything about my knees at all.  So they must have healed by themselves or those months where I followed the doctor’s orders were enough.