Astronauts’ Hearts Adapt to Spaceflight, Offering Hope for Future Mars Missions
A six-month stay in space may leave astronauts better prepared for the journey to Mars than scientists once feared. A study of 13 International Space Station crew members has found that their hearts adapted to prolonged weightlessness, with cardiovascular performance recovering towards pre-flight levels and no significant strain detected during a test simulating Martian gravity.
The research was led by scientists from Northwestern Medicine, UT Southwestern Medical Center, and UTHealth Houston, and published in the journal Circulation. It offers new evidence that the human cardiovascular system may cope with the transition from microgravity to the weaker gravitational pull of Mars, although further research will be needed before the findings can be applied to an actual landing.
On Earth, the heart works against gravity to circulate blood, while muscles support the body’s weight. In space, those demands fall, potentially reducing heart muscle mass and the amount of blood pumped with each beat.
Using ultrasound scans taken before, during, and after their missions, researchers tracked changes in the astronauts’ heart structure and function. During the first two weeks in orbit, measurements showed declines in cardiac filling and stroke volume, which describes the volume of blood pumped by the heart with each contraction.
However, these changes gradually eased as the astronauts adapted to life in orbit, with measurements approaching their pre-flight levels.
Daily exercise appears to have played an important role. Under NASA’s exercise programme, the crew members trained for up to two hours a day, combining endurance workouts to support cardiovascular fitness with resistance training to preserve muscle strength and mass.
The team then examined how their hearts responded to simulated Martian gravity after they returned to Earth. Mars has approximately 38 per cent of Earth’s surface gravity, meaning astronauts would face a different circulatory environment after months of weightlessness.
For the test, participants were tilted upwards by 22 degrees from a lying position to mimic some of the effects of gravity pulling blood towards the lower body. Their cardiovascular performance under this simulated condition was comparable to measurements taken while standing upright before their missions.
The findings suggest that the heart can adapt to prolonged spaceflight and retain the capacity to respond to a change in gravity. However, the study involved just 13 astronauts, and a ground-based simulation cannot fully reproduce the demands of arriving on Mars.
For future crewed missions, the results underline the importance of maintaining cardiovascular fitness throughout the journey, as researchers continue investigating how astronauts will cope with life beyond Earth.
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