I'm in my early 50s and for a couple of decades I've had occasional pains in my knees. But lately my legs feel really stiff and heavy and my knees hurt a lot more. It's quite painful getting out of chairs though I'm alright when I get going. I walk about an hour a day. Am just within the correct weight range for my height but would like to lose a few pounds. Anybody any idea what this could be? The stiffness and heaviness is quite alarming at times.