Standing still, pressure in the foot veins can reach 80 to 90 mmHg, and sitting still leaves the calf muscle pump just as switched off; once you walk, the calf muscles squeeze blood upward and, with working valves, bring it below 30 mmHg. That is why long periods of standing or sitting are listed as a risk factor for varicose veins, and getting up to walk a few steps, or raising your feet when you sit, is the usual advice.