WHAT COULD THE SORENESS AND STIFFNESS IN YOUR KNEE BE RELATED TO WHEN YOU BEND IT?
The first thing that comes to mind with a symptom like this is an orthopedic problem like some sort of arthritis like osteoarthritis. However, many other pathophysiological issues could be at work like a tendon or ligament pathology. The anterior (ACL) or posterior (PCL) cruciate ligaments could be damaged, the meniscus could be damaged or inflammed which would account for the symptom.
A myoitis of the anterior or posterior muscles of the thigh or tibial area could cause this or it could be something as simple as a tendonitis. A neuritis of the popliteal region may be at work. A more serious etiology may be present like peripheral arterial disease (PAD) which would produce intermittent claudication.
I suggest that if your symptoms persist, contacting your physician for a good physical exam and pointed questioning would be in order.
A sore and stiff knee could be related to multiple things. The first thing you would need to determine is if the pain is due to an injury or not.
The pain could be caused from Patellofemoral Syndrome, also called "runners knee," which is caused when the knee cap is not aligned properly and it grinds on other bones which causes soreness and stiffness. Anyone can get this, not just athletes. Pain and stiffness in the knee can also be caused by tendonitis, which is very common. In addition, carrying around extra weight can also cause pain as well. If the pain does not subside within a few days it is important to see a doctor so he or she can figure out exactly what is causing the knee pain. It is possible it could be related to another medical condition.