Something pretty cool happens every time you wiggle your toes. Your calf muscles squeeze veins deep in the lower leg and force blood upwards, against gravity, to your heart.
The same thing happens when you flex your ankle, climb the stairs, stand on tiptoes or take a walk.
It’s basic anatomical machinery – faintly miraculous when you stop to think about it, but so ubiquitous and normal that it’s often overlooked.
That could now be changing, however, as scientists wonder if this mechanism – known as the calf muscle pump function – could be a powerful lever to improve short- and long-term health.
In 2024, researchers at the Mayo Clinic looked at what happens when this function doesn’t work so well. They found that mortality rates increase quite dramatically for people with calf pump dysfunction.
Over a 10-year period, for example, the study showed that someone with normal calf pump function has a 5.9-per-cent risk of mortality. Over that same period, somebody with impaired calf pump function has a 17.5-per-cent risk of mortality.
It’s why the calf muscle is sometimes referred to as our ‘second heart’ – a term that isn’t overhyped, according to study author Dr Robert D McBane.
“The calf muscle is a very important physiological component of our cardiovascular system,” he says.
“Most people, when they think of pumping blood in the body, they think: ‘Yeah, we’ve got a pump. It’s called the heart.’ But the heart can only pump out the blood that’s returned to it.”
The calf is one mechanism in a chain of muscles that propel blood from the legs back to the heart. Muscles in the foot, thigh and abdomen also serve as valves.
“You can think of it like toothpaste. You’re squeezing one tube after another, and they’re ejecting the toothpaste north,” McBane says.
What’s different about the calf is that, first of all, it’s easier to study. We don’t have the equivalent measure of calf pump function for the thigh, for example.
Second, it’s a muscle that most of us can use more, meaning it’s potentially a literal lever that all of us can pull to improve our health.
Research suggests there are short-term benefits as well as the longer-term risk of mortality.
Good calf pump function means less blood pooling in the legs and ankles, reducing dull pain and discomfort. This may also contribute to the risk of things like swollen ankles and deep vein thrombosis.
Studies have also looked at a specific calf muscle called the soleus, which is active whenever we move about.
Researchers have shown that activating this muscle with low-level movements, even when people are seated, may improve the way our bodies process glucose after a meal.
Those low-level movements are easy. When seated comfortably, you simply raise your heels while keeping your toes on the ground. Then you repeat this for 5–10 minutes.
Researchers believe it’s a simple but powerful intervention for people with diabetes, as well as anyone who sits for long periods – because inactivity is one of the surest ways to lower your calf pump function.
Walking and running are two of the simplest ways to keep your second heart pumping. It’s another reason to get your 10,000 steps a day.
But McBane also says that other forms of exercise are important, including strength training to ensure this important muscle doesn’t waste as we age.
“I used to think – just personally – that the most important thing for good cardiovascular health was being aerobically fit. As long as you go for a run and keep fit aerobically, then you’re going to be okay,” he says.
“The reality is, we have to keep our anaerobic capacity too. You need to work hard to keep your muscles exercised and developed, and maintain muscle strength.”
Other forms of exercise may also be important, like stretching to maintain ankle mobility or balance training – again, especially with age – to make sure people are still able to walk and exercise regularly.
McBane adds that there’s data to support the idea that strengthening the calf muscles specifically – whether that’s at the gym or hiking – can improve calf pump function.
“What we don’t know yet is whether that also improves survival,” he says. “You could imagine that it would, but we haven’t yet taken the extra step in our research to show that this improves global health in the body.”
Even so, I’m heading off to the stair machine – who’s joining me?
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