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Scientists have long known that humans are built for endurance, with our shock-absorbing joints and springy tendons. Now, a new study shows people’s hearts are also optimized for endurance—though how much depends on whether we run, farm, or stay put on the couch.

To get to the heart of the matter, researchers used ultrasound imaging to examine the hearts of more than 160 adult men from four groups: long-distance runners, sedentary adults, highly trained football linemen, and the Tarahumara, Native American farmers renowned for their running ability. For comparison, they also looked at the hearts of 43 adult male chimpanzees—one of our closest evolutionary cousins.

When researchers compared the thickest of the heart’s four chambers—the blood-pumping, strawberry-shaped left ventricle—there were clear differences. Endurance runners and farmers had larger, elongated ventricles with thin walls—traits that help pump large volumes of blood for a long time, the researchers report today in the Proceedings of the National Academy of Sciences. The linemen, whose training emphasized short, high-intensity exercise, had shorter, wider ventricles with thicker walls. So did the sedentary humans. The chimps, whose main activities are short bursts of high-intensity exercise like fighting or climbing, had the shortest, thickest ventricles.

Because high-intensity activity causes blood pressure in the arteries to surge for a short amount of time, such small chamber volume, thick walls, and rounder shapes are beneficial to the linemen and chimps, researchers say, by making sure enough blood is still flowing to the brain to maintain consciousness. But even without those evolutionary pressures, a couch potato lifestyle seems to result in the same kind of thickening.

Adaptations for endurance likely helped our early hunter-gatherer and farming ancestors. But they also would have led to fewer parallel adaptations for problems like high blood pressure and cardiovascular disease—problems that run rampant in today’s industrial societies. Ironically, therefore, the researchers suggest those early endurance adaptations may have made it harder for modern populations to deal with hypertensive heart disease.

But sedentary readers shouldn’t feel heartbroken—the researchers emphasized that changes in heart shape are likely reversible, with the incorporation of endurance activities like distance running and swimming over many years. That’s one way to undergo a change of heart.

source: sciencemag.org

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