They are especially important because of the push and pull between the heart and the gravitational attraction of the ground, which bring the upward and downward flow of blood out of synch. For this reason, the feet are known as a "second heart."
加上地心引力牽制，使得腳部血液上行的費力程度和心臟搏出血液不相上下，因此也被稱為「第二個心臟」。