Over simplification for a gross biomechanical process. Knee pain is more related to hip dysfunctions or ankle dysfunctions and how each person gets there is specific to them. Generalizing and to say do this and do that because that is what works for everyone is a diservice to the client and the industry. Hamstrings also are a hip extensor and if they are inhibited for any reason they can also cause a dysfunction or inhibitory response to the Gluteals which will limit their ability to function. All muscles contract and fire, but receive less proprioceptive input as the tissue is shortening it's length. If their is a serious lack of input as it shortens the body will try to find a way to have other tissues related to the inhibited tissue to pick up the slack. In other words lose efficiency in the movement and increase the amount of load that related tissues have to handle, which can cause inhibition of those tissues as well. I would recommend seeking out a Muscle Activation Techniques Specialist (M.A.T) in your area to get a more thorough biomechanical analysis and assessment of what tissue is not able to handle load appropriately. I have been studying this process for the last few months and have seen some interesting results with clients and myself personally. I no longer "stretch" random muscles anymore hoping to increase ROM and decrease pain. Not saying stretching is bad, but taking a look only at a few muscles on the body and say they are weak/inhibited without taking a overall assessment of total lower extremity muscular function may potentially have you chasing your tail. Check out www.muscleactivation.com for a specialist near you or check for a Jump Start class
to potentially get in and get ready to look at the body in a different way than you have previously thought.