After spending nearly a year on the International Space Station (ISS), the largest cavity in the heart of astronaut Scott Kelly has been reduced to more than 25%.
Mr. Scott Kelly while living on the ISS Station. Photo: NYT In a study published in the journal Circulation on March 29, scientists found that during 340 days in space, Mr. Kelly’s heart was reduced in size even though he still exercised hard for 6 days. week. Luckily, the smaller heart did not seem to have any effect on the health of Mr. Kelly when he returned to Earth in 2016. This finding has added to the list of the types of transformations the human body has to undergo in an unstable environment of gravity. Astronauts also tend to have head edema, eyeballs crushing, leg shrinkage, and bones become more brittle. According to the New York Times, Dr. Benjamin D. Levine, study author and professor of internal medicine at the Southwestern Medical Center at the University of Texas (USA), said: “Kelly’s heart has changed to adapts to reduced gravity conditions. It does not have any dysfunction. He is still healthy. Without gravity, the heart doesn’t need to pump blood fully, and like any other muscle, it is altered by decreasing the intensity of the activity. For Mr. Scott Kelly, the shrinking phenomenon still occurs regardless of the regular exercise 6 days / week on the ISS. This regimen has been shown to be effective in reducing brittle bones and reducing muscle mass. After 340 days in space, Mr. Kelly’s heart weight dropped by about 27%, from 190 grams to 140 grams. Mr. Kelly shared that his body also underwent some other changes, such as bone loss, and these phenomena have almost returned to normal. However, the miniature heart phenomenon could be a concern for future missions to Mars. Based on the experiences of Mr. Kelly and other astronauts on the ISS, Dr. Levine thinks that the upcoming visitors to Mars will remain in good health. However, problems can arise if an astronaut is injured, becomes ill and cannot exercise, or if the exercise equipment is damaged. With weaker hearts, they can be dizzy and faint as they step onto the red planet after months of weightless travel. 
Swimmer Benoit Lecomte. Photo: CNN In the study, Levine and his colleagues compared the heart of astronaut Scot Kelly to that of long-distance swimmer Benoit Lecomte, when he tried to swim across the Pacific in 2018. The buoyancy in the water has the same impact on the body as the weightless environment. Lecomte athletes spend most of the day in the horizontal position: 8 hours of swimming and 8 hours sleeping on a support boat. Scientists think that extended swimming hours will be strenuous enough to maintain Mr. Lecomte’s heart size. But instead, it shrinks at a rate nearly as fast as Mr. Kelly’s time in space. After more than 159 days, the Lecomte athlete abandoned the plan after swimming two thirds of the planned 5,650 miles because the boat was destroyed by a storm. Through ultrasound, it was found that his left ventricle was about 28 grams lighter. The left ventricle is the heart’s largest and most powerful chamber, pumping blood to the aorta and throughout the body. Dr. Levine expressed surprise when she learned the results. “I thought his heart would get bigger. That is a huge amount of training ”. In an interview, Benoit Lecomte estimated his heart rate could be below 100 while swimming, and described the intensity of long-distance swimming as walking briskly, or running very slowly. Now, the US Aerospace Agency (NASA) can design better training programs for astronauts. In space, Mr. Scott Kelly has been exercising 6 days a week, 30-40 minutes walking on the treadmill or cycling. In addition, he also uses a resistance machine to lift weights. “This practice regime is quite strenuous. I have to push weights quite hard. The weight is definitely heavier than I can lift at home, ”said Kelly, now retired at NASA, in an interview. Dr. Benjamin D. Levine said there is another study to track the hearts of 13 astronauts before and after 6 months on the space station. This unpublished study will provide a broader amount of data.
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