For almost a year I spent practically all day sitting in front of a PC monitor (used to work at home), with no exercise.

Then I developed pain in both knees, worse on the left knee. I figured that it was because of too much sitting, so I got a standing desk. In about a month, knee pains gone, completely.

Never even bothered to go see a doctor.

After standing for too long, I started having pains in my lower back. Solution? I got a bar stool, so I now alternate between standing and sitting.

What I learnt is that our body's joints (knee, elbow, waist, ankle, etc) were not designed to remain in one position for too long. Movement lubricates them.