The most likely reason for standing for a long time is lower limb venous valve insufficiency. When standing, the calf is subjected to the greatest venous pressure because it is far from the heart, and when standing, the muscle activity of the calf is significantly reduced, the second heart of the calf, that is, the role of the muscle pump is significantly weakened, and the amount of blood returned to the heart is reduced, then the blood is stagnant inside the calf, which can cause distension and pain in the calf. Once this happens, ultrasound examination should be performed as soon as possible. Ultrasound examination can clarify the location of valve damage and the degree of valve insufficiency, and further treatment options can be determined based on the results of the examination, whether to perform surgery or conservative treatment.