The vessels that carry blood and other fluids (like veins and lymph vessels) depend on you moving to get the fluid away from your extremities and back into circulation. Also, diabetes and high blood pressure affect the kidneys' ability to excrete waste in the form of urine. Damage to these systems may cause the leg swelling. Of course, there are other causes that you should really discuss with your health care provider. Without a physical examination, it is difficult (nearly impossible) to find the cause of swollen legs.