When I examine someone for low back pain and/or knee pain we will often find poor hip extension.  Poor hip extension can be caused tightness in the front of the hip muscles, bony block of the hip joint or tightness of the hip capsules.  Another reason that we may be limited into hip extension is that the hip just does go into extension even though all the parts of the hip will go into extension on their own but when they are asked to the hip just says "NO".

I will often hit this issue from multiple different ways but a common way I address it is by performing a variant of the Triplanar Hip Matrix that was popularized by Gary Gray, PT.