Doctors suggest that during long periods of sitting, you should flex and extend your feet at the ankles periodically and squeeze your calf muscles to assist with blood circulation. Why would non-exercise muscle contraction affect blood flow and cardiovascular health?

The calf muscles act as pump and contracts to squeeze the blood vessels running through the legs. This makes the valves and the walls of the venous vessels to transport the venous blood back to the heart against gravity in an upward direction. If blood does not go back to the heart, it will be pooled in the legs leading to venous insufficiency and thus affects cardiovascular health. When the legs are in motion, the muscle pump works fine; but when we sit or stand for prolonged-time period without moving the legs or exercising, the muscles do not contract and the blood gets pooled in the legs, leading to various conditions like chronic venous insufficiency, varicose veins etc. Hence doctors suggest that during long periods of sitting, you should flex and extend your feet at the ankles periodically and squeeze your calf muscles to assist with blood circulation.