Bob Chen: if your knees feel uncomfortable while climbing mountains, that is due to your arthritis, which is strain of articular cartilage or ligament and soft tissue.  If your knees feel fine, but give you trouble in winter, then it is so-called “senile foot chilliness,” which is affected by the changes of temperature.  You must have plenty of preparatory activities to warm up your joints before any exercises.  

This problem is related to poor synovial fluid circulation inside your joints and joint wear and tear.  Therefore, this type of person can wear kneepads or heat packs to increase the temperature of their knee joints.  When the circulation of synovial joint fluid improves, the pain will be alleviated.