Researchers from Northwestern Medicine, UT Southwestern, and UT Houston monitored the hearts of 13 astronauts during approximately six-month stays aboard the International Space Station. Their findings, published in Circulation, show that astronauts' cardiovascular systems adapted well to microgravity, with intensive daily exercise protecting heart function.
Initial echocardiograms revealed declines in cardiac filling and stroke volume during the first two weeks in space. Over time, these measurements improved, approaching pre-mission levels. Astronauts exercised up to two hours daily as part of NASA's Exercise Countermeasures program, including 30 to 45 minutes of endurance training and 60 to 75 minutes of resistance work.
The study tested astronauts' hearts under simulated Martian gravity after they returned to Earth. Researchers tilted each astronaut 22 degrees from horizontal, causing blood to shift toward the lower body to approximate the effects of Mars's surface gravity, which is about 38% of Earth's. The astronauts' hearts performed as well under these conditions as they had standing upright on Earth before their missions.
"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 Dr. James Thomas, senior author and professor of cardiology at Northwestern University Feinberg School of Medicine. Study co-authors included Dr. Benjamin Levine of UT Southwestern Medical Center and Dr. Michael Bungo of the McGovern Medical School at UTHealth Houston.
The research addresses a primary NASA concern about human Mars missions. Extended microgravity causes heart muscle to shrink and weakens the cardiovascular system's ability to handle gravity. The astronauts' successful adaptation suggests that maintaining exercise regimens during spaceflight could enable crews to function on Mars without major cardiovascular strain.