Intense Exercise Needed to Prevent Heart Changes in Space
A study of an astronaut and an extreme long distance swimmer has shown that intense exercise is needed to prevent heart changes in space or situations of reduced weight, such as water immersion.
By comparing data from astronaut Scott Kelly’s year in space aboard the International Space Station and comparing it to information from Benoît Lecomte’s extreme long distance swimming, which simulates weightlessness, researchers found that low-intensity exercise was not enough to counteract the effects of prolonged weightlessness on the heart.
In a sitting or standing position, gravity draws blood into the lower extremities, and removing this effect through water immersion, prolonged bed rest or zero gravity conditions causes the heart to shrink as it no longer has to pump against this effect. Researchers have used the lack of gravity in space to investigate the physiology of ageing and muscle and bone loss, and vice versa.
Researchers examined data from retired astronaut Scott Kelly’s year-long mission aboard the ISS 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 effects of long-term weightlessness on the structure of the heart and to help understand whether extensive periods of low-intensity exercise can prevent the effects of weightlessness.
“The heart is remarkably plastic and especially responsive to gravity or its absence. Both the impact of gravity as well as the adaptive response to exercise play a role, and we were surprised that even extremely long periods of low-intensity exercise did not keep the heart muscle from shrinking,” said senior author Benjamin D Levine, MD, and a professor of internal medicine at UT Southwestern Medical Center and director of Texas Health Presbyterian’s Institute for Exercise and Environmental Medicine.
The research team examined medical data from Kelly’s year aboard the ISS and Lecomte’s swim across the Pacific Ocean to investigate the impact of long-term weightlessness on the heart. Water immersion is an excellent model for weightlessness since water offsets gravity’s effects, especially in the prone swimming technique used by long-distance endurance swimmers.
As part of the routine countermeasures to maintain physical fitness in space, Kelly exercised six days a week, one to two hours per day using a stationary bike, a treadmill and resistance activities. Researchers hoped Lecomte’s 159-day 2700km swim from Choshi, Japan, with almost six hours a day of swimming, would keep his heart from shrinking and weakening. Doctors performed various tests to measure the health and effectiveness of both Kelly’s and Lecomte’s hearts before, during and after each man embarked on his respective expeditions.
Both men and Lecomte lost mass from their left ventricles (Kelly 0.74 grams/week; Lecomte 0.72 grams/week). They also suffered an initial shrinkage in the diastolic diameter of their heart’s left ventricle (Kelly’s dropped from 5.3 to 4.6cm; 5 to 4.7cm for Lecomte).
Even the most sustained periods of low-intensity exercise were not enough to counteract the effects of prolonged weightlessness. Left ventricle ejection fraction (LVEF) and markers of diastolic function did not consistently change in either individual throughout their campaign.
Due to its exceptional nature, more study is required to understand how these results can be applied to the general population.
Lecomte had cardiac MRIs from before and after his swim and analysis of these is forthcoming. These will be helpful for the researchers to further understand whether long-term effects of weightlessness are reversible. Kelly did not receive cardiac MRIs, and currently, there are no further follow up plans for him.
Source: Medical Xpress
Journal information: Circulation (2021). DOI: 10.1161/CIRCULATIONAHA.120.050418