Final answer:
Sitting for a long time on a long airplane flight can lead to blood pooling below the knees and increase the risk of deep vein thrombosis (DVT).
Step-by-step explanation:
Sitting for hours on a long airplane flight can cause blood pooling below the knees due to a condition called deep vein thrombosis (DVT). DVT occurs when a blood clot forms in the deep veins, usually in the legs. When you sit for a long time, especially in cramped quarters, blood can pool in the deep veins of the legs, increasing the risk of a blood clot. Sitting for a long time on a long airplane flight can lead to blood pooling below the knees and increase the risk of deep vein thrombosis (DVT).