Patellofemoral pain syndrome (PFPS), also known as chondromalacia patella, causes knee pain when the patella does not track properly in the femoral grove. Often there is a relationship between tight quads, specifically the VLO and poor patellar tracking. 

The Vastus Lateralis Obliques (VLO) is the most lateral (outside) quad muscle and it goes all the way around the outer thigh under the IT Band to where the Hamstrings are. It is often a big trouble maker with IT Band syndrome as well.  Due to the VLO's position, and also the fact that the fibers come in at an oblique angle to the patella where they attach, the VLO can put a strong lateral pull on the patella, leading to tracking problems. 

Athletes such as skiers and trail runners often tend towards an imbalance between the VLO and the VMO (medialis), which results in a greater lateral pull at the patella. Its all physics!!  There can also be an imbalance between quads and hamstrings, and/or weakness of the gluteal muscles.  Whats the answer for avoiding PFPS?  Keep your quads supple, keep the hip abductors strong, maintain patellar mobility and maintain proper strength relationships between different muscle groups.  The Wave Tool is an essential tool in your bag of tricks and can be used to avoid this sharp knee pain when going downstairs and after sitting for a while.  Use the Wave Tool on the quads, IT band, and around the knee to decrease muscle trigger points, adhesions, and stiffness in the patellar attachments.    https://www.youtube.com/watch?v=_rad0pXDo2U&t=70s