The prospect of sleeping until Mars will have to overcome a critical Earth-related reality: the human heart needs high-intensity exercise to offset the effects of weightlessness, the researchers say.
The human heart shrinks when it is in a weightless environment for an extended period of time and low-intensity exercise is not enough to reverse the damage. Here on Earth, gravity plays a key role in maintaining the size of the heart, according to researchers at the University of Texas, so long-term exposure to weightlessness impairs the heart’s ability to function.
“The heart is remarkably plastic and particularly sensitive to gravity or the lack of it,” said Dr. Benjamin D. Levine, lead author of the study and professor of internal medicine at UT Southwestern Medical Center.
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.
The study team, the results of which were published in the journal Circulation on Monday, examined data from NASA astronaut Scott Kelly as he orbited Earth on the 2015 International Space Station. to 2016.
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This was then compared to data from French long-distance swimmer Benoit Lecomte, who spent six hours a day swimming part of the Pacific Ocean in 2018, to measure the long-term effects of weightlessness. Researchers believe that immersion in water is an excellent model of weightlessness, as water compensates for the effects of gravity, especially in a reclining swimmer like Lecomte.
Doctors carried out tests to measure the health and heart efficiency of the two men before, during and after the departure of each of their respective expeditions. Kelly spent 340 days on the ISS and exercised on a treadmill and stationary bike for at least an hour a day, while Lecomte spent six hours swimming while lying down.
Scientists reported that both men lost mass in their left ventricles, which also shrank in size. Kelly’s left ventricle diameter dropped from 5.3 cm to 4.6 cm (2 inches to 1.8 inches); Lecomte shrunk from 5 cm to 4.7 cm.
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The study indicates that every time a person sits or stands, gravity sucks blood into the legs. The work the heart does to maintain blood flow as it counteracts gravity helps it maintain its size and function – and removing the effects of gravity makes the heart shrink.
