Knee may become painful due to repeated use in certain activities. It may also be painful due to prolonged inactivity for some time. Both these reasons are distinct but cause pain in the knee joint.
Pain related to overuse is caused by chronic and repetitive micro trauma to the joint and its structures. This is usually related to sports and cause damage to local tissues and results in onset of discomfort and pain. While on the other hand, physical inactivity can cause wasting of the muscles and the tissues, making movement of knee difficult and painful.
The pain associated with overuse of knee joint can be described as pain that comes on gradually without a discrete inciting incident. While the pain associated with inactivity is more of stiffness and difficulty to move the knee for first few minutes.