I learned my lesson several months ago about running. I began cycling a little more than a year ago, and with the newfound fitness level that cycling brought on I began to jog and actually started thinking about 5k events etc. After a few weeks of light training with the running my knee flared up with pain and swelling. This was back in April. I stopped running and vowed to stay on the bike for all my endurance workouts. The knee is much better now, but it was only recently that the pain went away completely. Lesson learned: Stay on the bike!