You may not like it, but your heart is exactly what a peak endurance machine should look like. And if you don’t use that machine there could be serious health consequences, including a heart that looks a bit more “ape-like.”
Human hearts are on the thinner side, flexible, and capable of pumping out a massive volume of blood — about 2,000 gallons per day. In an analysis published Monday in Proceedings of the National Academy of Sciences, a team of scientists makes the case that those adaptations paid off in a big way by allowing our ancestors to become prolific hunters, gatherers, and runners — advantages that help set humans apart from our great ape relatives.
But even today, if we don’t use our finely tuned endurance machines, we can literally transform the way our hearts look and function. Robert Shave, Ph.D., study co-author and professor of health and exercise sciences at the University of British Columbia, tells Inverse that ignoring our heart’s needs can set the cycle of heart disease in motion.
“We have long known that physical activity, especially endurance physical activity (aka cardio) is good for the cardiovascular system, but this study helps explains WHY that is so,” Shave says. “Diet and stress matter, but an evolutionary perspective helps explain why an absence of endurance physical activity makes the cardiovascular system more vulnerable to disease.”
Why Your Heart Is Made for Working Out
In this study, Shave worked with Daniel Lieberman, Ph.D., an evolutionary biologist at Harvard, and Aaron Baggish, Ph.D., a cardiologist at Massachusetts General Hospital, to examine the evolution of the human heart. To do this, the team compiled heart data from endurance runners, football players, subsistence farmers, and healthy sedentary people. They compared all those hearts to chimpanzee and gorilla hearts — our ape relatives with whom we share roughly 99 and 98 percent of our DNA, respectively.
Compared to the chimp hearts the human hearts were elongated and slightly thinner. Chimpanzee hearts were rounder, thicker and smaller, and also filled with trabeculations, or folds down at the bottom of the left ventricle. Over time, the team suggests that humans actually lost those trabeculations, which allowed our hearts to twist slightly as they fill up with blood — a process called apical untwisting.
All together those adaptations add up to one thing: Our hearts became extremely well adapted to fill up with copious amounts of blood and then pump that blood efficiently throughout the body. That’s exactly what your body needs to do during moderate intensity physical exercise.
Chimps walk about two to four kilometers per day or perform short bouts high intensity activity like climbing or fighting, explains Lieberman. But hunter-gatherers, like early humans, needed endurance to cover huge distances. Having a heart that was able to pump more blood in an efficient way would come in useful when you have to cover so much ground:
“Hunter-gatherers, in contrast, have to walk long distances every day (9-15 km is the worldwide average), often carrying food and babies and they also spend hours a day digging and doing other moderate intensity tasks,” adds Lieberman.
In short, the team suggests that exercise played a role in transforming our hearts into the elongated, flexible things they are today. And even today, cardio continues continues to play a role in keeping them that way.
An “Ape-Like” Heart
Endurance exercise appears to be one of the key things that keeps our hearts looking partcularly human. And the types of exercise that we do (or don’t do) can change the way our hearts look.
For example, in the football player sample, the team found the offensive linemen who performed lots of strength training and comparatively little endurance training tended to have thicker, rounder hearts. The endurance runners, on the other hand, had far more flexible, elongated hearts.
These two opposite sides of the spectrum speak to the idea that the heart physically changes depending on the kind of exercise you do (both endurance and strength training have their advantages). The big idea behind the comparison is that our hearts are malleable. And not exercising also tends to alter our hearts as well.
When the team looked at the healthy, sedentary humans, they saw that they tended to have signs of an “intermediate phenotype.” In short, their hearts started to remodel and develop thicker walls and a rounder shape that was reminiscent of the hearts seen in chimpanzees.
Shave adds that this is important because these changes were seen in healthy, sedentary adults, suggesting that exercise itself can play a role in helping the heart maintain its structure even before conditions like high blood pressure set in.
“It is also important to note that the sedentary individuals start to show evidence of remodeling even in the absence of high blood pressure, this underpins the the importance of lifelong activity,” says Shave.
Once that thickening gets started, it kicks off a cycle, the team proposes. Thickening can lead to higher blood pressure, which in turn can lead to even more remodeling. Over the course of a lifetime, the team writes that this can “culminate” in heart disease.
“Our findings in this paper not only emphasize the importance of exercise with aging but the importance of starting and maintaining healthy physical activity patterns very early in life,” says Baggish. “In essence, the absence of adequate physical activity even in people [in their] 20s and 30s appears to confer later health risks.”
The authors add that they’ll have to test this hypothesis more fully. But right now, it points to the importance of setting up a moderate exercise routine. Your heart is an endurance machine that’s meant to be used, and when it’s left to rust for too long, it can lead to problems down the line.
Chimpanzees and gorillas, when not inactive, engage primarily in short bursts of resistance physical activity (RPA), such as climbing and fighting, that creates pressure stress on the cardiovascular system. In contrast, to initially hunt and gather and later to farm, it is thought that preindustrial human survival was dependent on lifelong moderate-intensity endurance physical activity (EPA), which creates a cardiovascular volume stress. Although derived musculoskeletal and thermoregulatory adaptations for EPA in humans have been documented, it is unknown if selection acted similarly on the heart. To test this hypothesis, we compared left ventricular (LV) structure and function across semiwild sanctuary chimpanzees, gorillas, and a sample of humans exposed to markedly different physical activity patterns. We show the human LV possesses derived features that help augment cardiac output (CO) thereby enabling EPA. However, the human LV also demonstrates phenotypic plasticity and, hence, variability, across a wide range of habitual physical activity. We show that the human LV’s propensity to remodel differentially in response to chronic pressure or volume stimuli associated with intense RPA and EPA as well as physical inactivity represents an evolutionary trade-off with potential implications for contemporary cardiovascular health. Specifically, the human LV trades off pressure adaptations for volume capabilities and converges on a chimpanzee-like phenotype in response to physical inactivity or sustained pressure loading. Consequently, the derived LV and lifelong low blood pressure (BP) appear to be partly sustained by regular moderate-intensity EPA whose decline in postindustrial societies likely contributes to the modern epidemic of hypertensive heart disease.