It implies that the capacitance vessels (i.e. the veins) of the leg dilate and contain a larger share of the body's blood than they otherwise would. I just don't understand why this should happen any more after exercise than it should at any other time. In general, there are 2 mechanisms that work against this. First, the muscles of the legs have a pumping action--when the muscles contract, they squeeze the veins, and second, the veins of the legs have valves (other veins do, too, but not as many as in the legs) to help assure one-way flow of the blood. So when you are moving your legs, you are helping to pump blood back to the CNS. That's why they tell you to get up and walk around during long airline flights to help decrease the chance of blood clots in the legs.
I think that this is a greater issue while sitting in traffic for an hour than it is to leave the the fun run without some formal cool-down.
haha you nailed it doc. Sometimes some people's valves don't work correctly which could result in damaged veins like vericose veins and supposedly lead to those arrythmias because the blood doesn't return fast enough to the heart....