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What do long-distance swimming and spaceflight have in common? They can both shrink the heart, according to a new study.
Both activities reduce pressure gravity on the heart, so it doesn’t have to work as hard to pump blood upward through the body. The heart is a muscle, and like any other muscle in the body, if it isn’t used as much as it used to be, it will shrink.
To understand the effect of weightlessness on the heart, a group of researchers analyzed year-round health data for retired astronaut Scott Kelly aboard the International Space Station from 2015 to 2016, and health data from elite endurance swimmer Benoît Lecomte, who swam 1753 miles (2,821 kilometers). ) across the Pacific Ocean in 2018.
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Lecomte swam 159 days between June 5 and November 11, 2018, taking 7 and 32 day breaks due to inclement weather conditions (which was a limitation in data collection but was for his own safety) , according to the study. He swam about 5.8 hours a day, on average.
Kelly spent 340 days in space and exercised a few hours a day, 6 days a week by cycling, using the treadmill and doing resistance exercises. Doctors analyzed the hearts of the two men before, during and after their respective trips.
The researchers found that during her year in space, Kelly lost about 0.74 grams of heart mass per week in her left ventricle, the heart’s main pumping chamber. Lecomte, while crossing the Pacific, lost 0.72 grams of heart mass per week in his left ventricle. The researchers also found that when Kelly and Lecomte began their journey, both men suffered an initial drop in the diameter of their left ventricle. The average heart is around 280 to 340 grams in men and 230 to 280 grams in women, according to Live Science.
Overall, Kelly suffered a loss of left ventricular mass of 19% to 27% during his year in space and Lecomte suffered a loss of 20 to 25% during the five months he was swimming, University of Texas Southwestern Medical Center at Dallas told BBC.
In other words, despite exercising in a weightless environment (water and space), both men’s hearts shrank during their travels. This was surprising to scientists, because high-intensity swimming training for 1 to 3 hours per day has already been associated with an increase in the size and mass of the left ventricle. “We expected that a long duration of swimming exercise was enough to stimulate,” to increase left ventricular mass, the authors wrote.
“The heart is remarkably plastic and particularly sensitive to gravity or the lack of it,” lead author Dr. Benjamin Levine, professor of internal medicine at UT Southwestern Medical Center said in a press release. “The impact of gravity as well as the adaptive response to exercise play a role, and we were surprised that even very long periods of low-intensity exercise didn’t stop the heart muscle from shrinking.”
But after their travels, both men’s hearts returned to their normal size once they returned to walking on the ground, according to the BBC. The researchers still plan to analyze magnetic resonance imaging (MRI) scans of Lecomte’s heart before and after his swim to better understand whether the long-term effects of weightlessness can be completely reversed, according to the release.
The results were published on March 29 in the journal Circulation.
Originally posted on Live Science.
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