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October 21, 2026ronauts suggests that the human heart may be surprisingly well equipped for a journey to Mars, especially with regular exercise during spaceflight. Researchers found that astronauts’ hearts adapted to months of weightlessness and handled simulated Martian gravity without major problems, offering new hope for future missions to the Red Planet.
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A journey to Mars may be less challenging for the human heart than scientists once feared. A new study suggests that astronauts can adapt remarkably well to months of weightlessness, offering encouraging evidence that humans could endure the long trip to the Red Planet and function under its weaker gravity.
Researchers from Northwestern Medicine, UT Southwestern, and UT Houston monitored the hearts of 13 astronauts who spent approximately six months aboard the International Space Station. Their findings showed that although spaceflight initially affected heart performance, the astronauts gradually adapted, with intensive daily exercise playing an important role in maintaining their cardiovascular health.
One of NASA’s major concerns about sending humans
One of NASA’s major concerns about sending humans to Mars is how astronauts’ hearts and circulatory systems will respond when they leave the weightless conditions of spaceflight (known as microgravity) and encounter Martian gravity, which is only about one-third as strong as Earth’s.
Encouragingly, the researchers found that the astronauts showed no significant signs of cardiovascular strain when exposed to simulated Martian gravity after returning to Earth.
“With our findings, there is now reason to think that we would be able to traverse to Mars, get there and actually work on the surface of Mars,” said study senior author Dr. James Thomas, professor of medicine in the division of cardiology at Northwestern University Feinberg School of Medicine.
The study, published last month in the journal
The study, published last month in the journal Circulation, is the first to investigate how the heart responds to simulated Martian gravity following an extended period in space.
How Daily Exercise Protects Astronauts’ Hearts in Space
Living without gravity creates unusual challenges for the human body. On Earth, the heart constantly works against gravity to circulate blood, while muscles must support the body’s weight. In space, those demands decrease substantially, allowing muscles and even the heart itself to shrink over time.
Returning to a gravitational environment can also be difficult. Astronauts on previous missions have frequently experienced dizziness or lightheadedness when standing after landing. This happens because gravity pulls blood toward the lower body, sometimes causing blood pressure to drop suddenly. The condition is called orthostatic hypotension. (If you’ve seen Sandra Bullock crawling after returning to Earth in “Gravity,” you get the idea.)
The astronauts involved in the new study generally
However, the astronauts involved in the new study generally handled this transition well, potentially because they had maintained demanding exercise schedules throughout their missions.
As part of NASA’s Exercise Countermeasures program, astronauts exercised for up to two hours each day. Their routines included 30 to 45 minutes of endurance training, which strengthens the cardiovascular system, along with 60 to 75 minutes of resistance training to help preserve muscle mass and strength.
“You lose muscle mass and cardiac mass when you’re in a weightless environment because you are working less up there,” explained Thomas, who also is a Northwestern Medicine cardiologist. “You’re floating around in the air, and you give a little tap with your foot, and you can sail over to say hello to your buddy.”
“To counter that, exercise is crucial when you’re in space,” Thomas added.
Heart Scans Reveal How the Body Adapts to Weightlessness
To understand what happens to the heart during
To understand what happens to the heart during prolonged spaceflight, the researchers collected echocardiograms before, during, and after each astronaut’s mission. These ultrasound scans use sound waves to produce moving images of the heart, allowing doctors to examine its structure and measure how effectively it pumps blood.
While aboard the International Space Station, astronauts were trained to perform these scans on one another every few weeks. The recordings were transmitted to Earth, where researchers could monitor changes in heart function throughout the missions.
Thomas worked alongside Dr. Benjamin Levine of UT Southwestern Medical Center and Dr. Michael Bungo of the McGovern Medical School at UTHealth Houston.
It would be typically about 3 a.m
“It would be typically about 3 a.m. for me because the space station runs on Greenwich Mean Time,” Thomas said. “I would watch the recordings come in live and coach the astronauts in real time to improve the images.”
The scans revealed that the astronauts’ hearts initially struggled to adjust to their new environment. During the first two weeks in space, researchers observed declines in cardiac filling, stroke volume, and several other measures of cardiovascular performance.
Cardiac filling refers to how much blood enters the heart between beats, while stroke volume describes the amount of blood pumped out with each contraction. Both measurements decreased early in the missions, indicating that the astronauts’ hearts were temporarily moving less blood with each beat.
But the changes did not persist.
As the astronauts spent more time in space,
As the astronauts spent more time in space, their cardiovascular systems adapted. Cardiac filling and stroke volume gradually improved, approaching the levels recorded before launch.
These results suggest that the heart can adjust to prolonged weightlessness more effectively than early measurements might indicate, particularly when astronauts maintain regular physical activity.
Astronauts’ Hearts Pass a Simulated Mars Gravity Test
The researchers also wanted to answer a particularly important question for future Mars missions: What happens when an astronaut who has spent months in weightlessness suddenly encounters gravity again?
Mars has roughly 38% of Earth’s surface gravity
Mars has roughly 38% of Earth’s surface gravity. Although this is considerably weaker than what people experience on Earth, it would still force astronauts’ hearts to work differently after months of floating in space.
To reproduce some of these effects, the researchers conducted a simulated Martian gravity test after the astronauts returned to Earth.
Each astronaut was tilted upward by 22 degrees from a lying position. This posture caused blood to shift toward the lower body, approximating the circulatory effects of Martian gravity.
The results were encouraging
The results were encouraging. After spending about six months in space, the astronauts’ hearts performed just as well under simulated Martian gravity as they had when standing upright on Earth before their missions.
This suggests that astronauts who maintain their cardiovascular fitness during spaceflight may be capable of transitioning to the weaker gravity of Mars without experiencing major cardiovascular difficulties.
Although the findings come from a relatively small group of astronauts and a simulation rather than an actual Mars landing, they provide valuable evidence for planning future missions.
Combined with the benefits of daily exercise,
Combined with the benefits of daily exercise, the heart’s ability to adapt to weightlessness and respond well to simulated Martian gravity offers another reason to be optimistic about sending humans to the Red Planet.
The study is titled “Impact of Prolonged Spaceflight on Cardiac Structure and Function: An Exploratory Longitudinal Observational Study.” Funding was provided by the National Space Biomedical Research Institute (grant NCC9-58), NASA (grant NNJ04HH01A), the IDP Foundation, Sandra Helton, and the National Heart Foundation of Australia.
Materials provided by Northwestern University. Note: Content may be edited for style and length.
- Vinesh Appadurai, Kazuaki Negishi, Allen G. Borowski, Zoran B. Popović, Neil L. Greenberg, David S. Martin, Michael W. Bungo, Benjamin D. Levine, James D. Thomas. Impact of Prolonged Spaceflight on Cardiac Structure and Function: An Exploratory Longitudinal Observational Study. Circulation, 2026; 154 (15): 1444 DOI: 10.1161/CIRCULATIONAHA.125.078665
Northwestern University. “Astronauts’ hearts just passed a surprising test for Mars.” ScienceDaily. ScienceDaily, 21 October 2026. <www.sciencedaily.com/releases/2026/10/261020085016.htm>.
Northwestern University. (2026, October 21). Astronauts’ hearts just passed a surprising test for Mars. ScienceDaily. Retrieved October 21, 2026 from www.sciencedaily.com/releases/2026/10/261020085016.htm
Northwestern University. “Astronauts’ hearts just passed a surprising test for Mars.” ScienceDaily. www.sciencedaily.com/releases/2026/10/261020085016.htm (accessed October 21, 2026).
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