When astronaut Scott Kelly spent nearly a year in space, his heart shrank despite the fact that he worked out six days a week over his 340-day stay, according to a new study.
Surprisingly, researchers observed the same change in Benoît Lecomte after he completed his 159-day swim across the Pacific Ocean in 2018.
The findings suggest that long-term weightlessness alters the structure of the heart, causing shrinkage and atrophy, and low-intensity exercise is not enough to keep that from happening. The study published Monday in the American Heart Association’s journal Circulation.
Photo : CNN
The gravity we experience on Earth is what helps the heart to maintain both its size and function as it keeps blood pumping through our veins. Even something as simple as standing up and walking around helps pull blood down into our legs.
When the element of gravity is replaced with weightlessness, the heart shrinks in response.
Kelly lived in the absence of gravity aboard the International Space Station from March 27, 2015, to March 1, 2016. He worked out on a stationary bike and treadmill and incorporated resistance activities into his routine six days a week for two hours each day.
Lecomte swam from June 5 to November 11, 2018, covering 1,753 miles and averaging about six hours a day swimming. That sustained activity may sound extreme, but each day of swimming was considered to be low-intensity activity.
Even though Lecomte was on Earth, he was spending hours a day in the water, which offsets the effects of gravity. Long-distance swimmers use the prone technique, a horizontal facedown position, for these endurance swims.
Researchers expected that the activities performed by both men would keep their hearts from experiencing any shrinkage or weakening. Data collected from tests of their hearts before, during and after these extreme events showed otherwise.
Kelly and Lecomte both experienced a loss of mass and initial drop in diameter in the left ventricles of the heart during their experiences.
Both long-duration spaceflight and prolonged water immersion led to a very specific adaptation of the heart, said senior study author Dr. Benjamin Levine, a professor of internal medicine/cardiology at the University of Texas Southwestern Medical Center.
While the authors point out that they only studied two men who both performed extraordinary things, further study is needed to understand how the human body reacts in extreme situations.
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