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 Earth’s gravity helps it maintain its size and function. Removing gravitational effects causes the heart to shrink.
Researchers examined data from retired astronaut Scott Kelly’s passage aboard the International Space Station from 2015 to 2016 and elite endurance swimmer Benoît Lecomte’s swim across the Pacific Ocean in 2018 .
In this new study, researchers evaluated the long-term effects of weightlessness on the structure of the heart and to help understand whether long periods of low-intensity exercise can prevent the effects of weightlessness.
The heart is remarkably plastic and above all sensitive to gravity or the lack of it. 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. ”
Benjamin D. Levine, MD, lead study author and professor of internal medicine, UT Southwestern Medical Center and director, Texas Health Presbyterian’s Institute for Exercise and Environmental Medicine
The research team looked at Kelly’s Year’s health data in space aboard the International Space Station and Lecomte’s swim across the Pacific Ocean to study the impact of weightlessness at long term on the heart. Immersion in water is an excellent model of weightlessness because water compensates for the effects of gravity, especially in a recumbent swimmer, a specific swimming technique used by long distance endurance swimmers.
Kelly exercised six days a week, one to two hours a day during her 340 days in space, from March 27, 2015 to March 1, 2016, using a stationary bike, treadmill and resistance activities. . Researchers hoped that Lecomte’s 159-day swim from June 5 to November 11, 2018, 1753 miles from Choshi, Japan, during which he swam an average of nearly six hours a day, would keep his heart from shrinking and sagging. ‘weaken. Doctors performed various tests to measure the health and efficiency of Kelly and Lecomte’s hearts before, during and after each man embarked on their respective expeditions.
The analysis revealed:
- Kelly and Lecomte both lost mass in their left ventricles during the experiments (Kelly 0.74 gram / week; Lecomte 0.72 gram / week).
- Both men suffered an initial drop in the diastolic diameter of the left ventricle of their heart (Kelly’s fell from 5.3 to 4.6 cm; Lecomte’s from 5 to 4.7 cm).
- Even the most prolonged periods of low-intensity exercise were not sufficient to counteract the effects of prolonged weightlessness.
- Left ventricular ejection fraction (LVEF) and markers of diastolic function did not change consistently in the two individuals throughout their campaign.
This case study examined two extraordinary feats of two unique individuals. While it is important to understand how the body reacts to extreme circumstances, more studies are needed to understand how these results can be applied to the general population. Lecomte’s cardiac MRI scan before and after his swim is upcoming and will also help researchers better understand whether the long-term effects of weightlessness can be reversed. Kelly has not received a cardiac MRI and currently there are no other follow-up plans with him.
American Heart Association