I recently attended a cycling event indoors and after 2 hours of intense cycling I start feeling my legs tightening up in the quads. Then some 3 hours after that I started suffering acute pain in the quads whereby I could hardly walk and getting up from seated position was extremely difficult ands stairs were virtually impossible. Some 3 days later I am no better and the legs are still very tender. When cycling I often get chronic cramping in the quads. What is causing this