When you are standing still cooking you are not using your muscle pump action to move the liquid upstream. Thus, the blood flow pools in the foot, ankle, and lower leg. This starts the process of swelling. As more liquid accumulates at the bottom of the foot and ankle it is difficult for the liquid to move upstream. The veins enlarge and the valves inside the veins that ensuring a one-way flow cannot close an approximate. This causes a cycle in which the blood flows to the foot, stays there and has a difficult time flowing upward in the veins back to the heart. As the liquid (blood) remains stagnant, fluid moves into spaces outside of vessels leading to tired, aching, and heaviness in the foot and leg.