The calf muscle in your legs is your second heart.
Everyone knows that the heart pumps blood, right? But did you know that your body has a second blood pump? It’s your calf muscles! That’s right, the calf muscles in your legs are your second heart!
The human body is engineered such that when you walk, the calf muscles pump venous blood back toward your heart.
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 up along the venous system. These veins have one-way valves which keep the blood flowing in the correct direction toward the heart, and also prevent gravity from pulling blood back down your legs.
Walking or running enables your foot to play a major role in the pumping mechanism of the calves. The foot itself also has its own (smaller) venous reservoir. During the first 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.
Thus, when you are immobile for long periods of time (sitting in an airplane, car seat, or chair for hours) your calf muscle is not contracting much and the blood stagnates.
That’s why walking or running is so good for overall blood circulation. It prevents blood pooling and helps prevent potentially dangerous blood clots called deep vein thrombosis(DVT).
Another condition called venous insufficiency, or venous reflux can cause blood to pool in your legs due to the failure of the valves to work properly. In this condition, the valves fail to prevent the backflow of blood down your legs. Symptoms of venous insufficiency can include heavy, tired, throbbing, painful legs, ankle swelling, bulging varicose veins, cramps, itching, restless leg, skin discolouration 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 (DVT). DVT can cause leg pain and swelling and is dangerous because a blood clot can break off and travel in your blood stream and get lodge in your lungs.