The evolution of walking on two feet freed our hands, but it also created a challenge for our circulation. Located far from the heart, the calf muscles help push blood upward against gravity. Vascular specialists sometimes call the calf muscle pump a “second heart.” Yet despite using these muscles thousands of times a day, most of us pay little attention to them until something goes wrong. I did, too. Even as a vascular researcher and active athlete, I largely ignored my calves until I began training for a hybrid endurance-and-strength race. Recurrent lower-leg discomfort and instability made me realize how easily this frequently used muscle group can be neglected.
When we stand, the pressure in the veins near our ankles rises dramatically compared with when we lie down. Every time we walk, our calf muscles contract, squeezing the deep veins and pushing blood upward, while one-way valves help keep it from flowing backward as the muscles relax. This repeated contraction and relaxation creates a pump that helps move blood from the lowest part of the body back toward the heart. When this pump becomes less effective, the consequences can go beyond athletic performance.
Chronic venous disease, which affects more than 25 million adults in the United States, is not simply a disease of weak calf muscles. But poor calf-pump function can contribute to and worsen the disease by making it harder for the legs to move blood toward the heart. Blood that pools in the lower legs can contribute to varicose veins, leg heaviness, swelling, skin changes, and, eventually, venous ulcers. A recent Mayo Clinic study found that calf-pump function progressively declined as chronic venous disease became more severe. Poor calf-pump function was associated with 84 percent higher odds of active or previously healed venous ulcers.
This relationship can also become a vicious cycle. Venous disease causes aching, swelling, and heaviness in the legs, making people less inclined to move. Less movement activates the calf pump less often, making it even harder to move blood out of the legs. Poor calf function may therefore contribute to venous dysfunction while also worsening as disease and inactivity progress. Encouragingly, a recent randomized clinical trial found that adding calf-strengthening exercises to compression therapy, a standard treatment for chronic venous disease, improved calf strength, ankle mobility, disease severity, and quality of life more than compression therapy alone.
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Although easy to ignore, our calves are relatively easy to train. Simply spending all day on your feet does not necessarily exercise the calf pump. Standing still for long periods keeps pressure high in the veins of the lower legs; movement is what activates the pump. And that movement does not require a gym. Walking, repeated heel raises, and moving the ankles up and down all activate the lower-leg muscles. For people who spend much of the day sitting or standing, taking short walking breaks or regularly moving the ankles may be more beneficial than remaining still in either position. More structured calf-strengthening exercises can further improve strength, mobility, and stability.
This may become even more important as we age. Aging is accompanied by a gradual loss of muscle mass and strength, potentially weakening both our mobility and the calf pump that helps move blood out of our legs. A recent Canadian study comparing younger and older adults found age-related changes in blood flow from the lower legs and reduced efficiency of the calf muscle pump. Preserving calf strength and staying active as we age, therefore, may matter not only for staying mobile but also for maintaining the pumping mechanism that helps move blood back toward the heart.
We spend enormous effort thinking about the organ at the center of our circulation while paying less attention to what happens at its most distant point. When humans transitioned to standing and walking on two feet, the calf muscle pump became part of our solution to the gravitational challenge of returning blood to the heart.
Strong calves cannot prevent every vascular disease, and calf exercises cannot replace appropriate cardiovascular care. But these muscles deserve to be viewed as more than tools for running faster or jumping higher. They help us move, and movement helps them move our blood. Preserving their strength may therefore be one of the simplest things we can do for two abilities that become increasingly valuable as we age: circulation and mobility.
Wei Zhang is a postdoctoral researcher.
