http://gravitywerks.com Mobility and natural flexibility is vital to comfortable hips and knees. We can do the very same things that animals do, which is to pandiculate and use the brain to change how our muscles respond.
No worries on the long "p" word, we've systematized that and this is what is known as somatics exercises which are the reverse to most things out there. Simple, easy movements afford us the ability to move comfortably.
Try the move in this video. You might have to learn a few things before your hips are ready and your knees are comfortable. Setting up movement is vital to our health and we can all learn how to do simple somatics exercises so movement feels good once again and again.