Everyone knows that the heart pumps blood, right? Did you know that your body has a second blood pump? It’s your calf muscles! That’s right, your calf muscles are your second heart! The body is engineered so that when you walk, the calf muscles pump venous blood back toward your heart.


diagram showing blood flow in the calf


The veins in your calf act like a reservoir for blood your body does not need in circulation at any given time. These reservoir veins are called muscle venous sinuses. When the calf muscle contracts, blood is squeezed out of the veins and pushed along the venous system. One-way valves in the leg veins keep the blood flowing in the correct direction toward the heart. These valves also prevent gravity from pulling blood back down your legs veins in the wrong direction.

When you walk, your foot plays a role in the pumping mechanism as well. The foot also has a (smaller) venous reservoir. During the early motion of taking a step, as you put weight on your foot, the foot venous reservoir blood is squeezed out and ‘primes’ the calf reservoir. Then, in the later stages of a step, the calf muscle contracts and pumps the blood up the leg, against gravity. The valves keep the blood flowing in the right direction and prevents gravity from pulling the blood right back down.

When you are immobile for long periods of time, say in an air plane seat or car seat, or sitting at a desk for hours, your calf muscle is not contracting much and blood pools.

That’s why walking is so good for the circulation in your legs! Walking prevents blood pooling and helps prevent potentially dangerous blood clots called deep vein thrombosis, or DVT.

Also, a condition called venous insufficiency, or venous reflux, can cause blood to pool in your legs due to failure of the one-way valves to work properly. In this condition, the valves are not competent and allow blood to flow backwards back down your leg. The valves are said to be “leaky”. Symptoms of venous insufficiency can include heavy, tired, achy, throbbing, painful legs, ankle swelling, bulging varicose veins, cramps, itching, restless leg, skin discoloration and even skin ulceration. Venous insufficiency is a very common disorder, affecting over 40 million people in the U.S.

In cases when a person is even more immobile, such as laying in a hospital bed, the pooled blood can become stagnant and develop into a blood clot. This is called a deep vein thrombosis, or DVT. DVTs can cause leg pain and swelling. Sometimes they do not cause any symptoms. DVTs can be dangerous because a blood clot can break off and travel in your blood stream and lodge in your lungs.


Written by Louis Prevosti, MD

If you have some of the symptoms listed above, or you think you have blood pooling, venous insufficiency, or a blood clot, call or email to set up a consultation with our vein specialists.