After speaking with many health professionals, I am beginning to understand how PFS starts. No, it isnt necessarily from overuse of your knee, or running on hard ground. For men and women, it is the placement of your foot! Yes, an overpronating foot (80% of the population!) will cause your enjoy body to be out of balance and your knees will carve inwards, toward one another. Obviously, there is additional strain placed on your knees as a result. For women, wide hips also contribute to additional stress on the knees by increasing the Q-angle (angle between the knee and the edge of the hips, which is obviously larger on women). As a young man, I was 17 when it started in the right knee. Later, it spread to the left, and when the pain was intense I decided to see a doctor and was diagnosed with PFS. I started PT and that helped significantly, but the pain is still there. It took me many months to finally get arch-supporting shoes and inserts, and they have helped tremendously. I plan on getting custom-made orthotics done in the near future to perfect this foot problem. My point is, if your knees are aching, chances are its from your wide hips (if you are female) or have pronating feet, which 80% of you do. Get arch supports and the correct shoes before your condition degenerates into CP!