People always wonder why areas of injury or surgery hurt more so many hours after activity has stopped or when they are just plain resting at night and not moving at all. The reason for this all too true phenomenon is the fact that the site of surgery has extra vessels (to provide the cells that will clean up the debris and provide the components of healing) as well as swelling (as a normal response to injury/surgery) in the tissues. As the activity level increases so does the flow of blood which increases swelling even more. Pain is directly proportional to swelling which proportional to activity. Each follows the other with a lag time of 2-4 hours, which explains why most of our pain occurs in the evening while we are resting. We pay for the sins we commit by day, at night.