Accumulation of blood in the veins of legs over a long period of time, as may occur in people with occupation that require standing still for long hours can lead to stretching of veins to a point where venous valves no longer are efficient. Even the leg muscles (especially Soleus) do not contract to compress the veins for upward movement of the blood. This causes pooling of blood in the leg veins, as the blood is unable to ascend against gravity. This leads to gnarled, enlarged veins, most commonly appearing in the legs and feet. This condition is known as "varicose veins".