A study of 13 astronauts suggests that daily exercise may help protect heart function during long space missions, allowing crews to work on Mars after months in space.
After months on the International Space Station, astronauts have often struggled the first time they stood up back on Earth. Some got dizzy or lightheaded.
For a crew bound for Mars, that’s a real worry, because they would land on another planet and then need to work there.
A new study of 13 astronauts suggests the heart may hold up. After about six months in orbit, the astronauts’ hearts handled simulated Mars gravity as well as they had handled standing upright on Earth before launch.
The findings suggest that astronauts who maintain their daily exercise routines may be able to stand and work on Mars after a six-month journey.
James Thomas, a professor of medicine in the Division of Cardiology at Northwestern University Feinberg School of Medicine, was the study’s senior author.
“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,” Thomas said.
Nine of the astronauts were men, and the group’s average age was 49. The typical mission lasted 164 days.
Why standing up gets hard
Gravity pulls blood toward the lower body. After months without it, a person who stands up can have a sudden drop in blood pressure.
Doctors call this orthostatic hypotension, and it’s the reason many returning crew members have struggled with dizziness on their feet.
Mars raises a different version of the problem. Its gravity is about 38% of Earth’s.
NASA has needed to know whether a crew’s hearts and blood vessels could manage the jump from weightlessness on the trip to Mars to a planet with that much pull.
Two hours of exercise daily
The astronauts followed a NASA program called Exercise Countermeasures. They worked out for up to two hours a day. Each session included 30 to 45 minutes of endurance exercise and 60 to 75 minutes of resistance training.
“You lose muscle mass and cardiac mass when you’re in a weightless environment because you are working less up there,” said Thomas, who is also 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,” he said.
Scanning hearts in orbit
The team followed each heart with ultrasound. Doctors call an ultrasound scan of the heart an echocardiogram, and each astronaut had them before, during and after the mission.
In orbit, the astronauts were trained to scan one another every few weeks. The images went down to Thomas and his team on the ground, who tracked how each heart’s size and pumping changed over time.
Many of the measurements focused on the left ventricle, the chamber that pumps blood out to the body.
“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.”
Thomas worked with Benjamin Levine of UT Southwestern Medical Center and Michael Bungo of McGovern Medical School at UTHealth Houston.
Early changes faded
The astronauts’ hearts changed most in the first two weeks of the flight. Between beats, each heart filled with less blood than before, and each squeeze pushed out less of it.
The heart muscle also stretched and shortened less with each beat.
Before launch, the astronauts’ hearts had shown drops of a similar size on Earth, just from going from lying flat to upright. So two weeks of weightlessness did roughly what standing up does to the heart.
The astronauts’ hearts didn’t stay that way. As the missions went on, the amount of blood filling the heart and the amount pumped with each beat both rose.
Each got closer to the level measured before launch, when the astronauts were lying down.
Hearts handled the Mars tilt
For the Mars test, the researchers had each astronaut lie down and then tilted them 22 degrees head-up. The tilt shifts blood toward the lower body to mimic standing in Mars gravity.
The astronauts took that test before launch and again after they came home from about six months in space.
On the return test, none of the measures of heart volume or blood flow showed more strain than the same hearts had shown standing upright on Earth before the flight.
Standing up in Earth’s full gravity is the bigger load of the two. These hearts had managed that every day before launch.
What the study can’t say
The authors call their work a small, exploratory study. They followed one group of astronauts over time rather than comparing two groups. Every astronaut in it was following the same exercise plan.
On top of that, the Mars test used a tilted table in a lab rather than a real landing. The flights lasted up to about six months.
The researchers didn’t test what happens to a heart without the workouts.
For now, the evidence comes from 13 astronauts and a table tilted 22 degrees. Researchers would need to follow a larger group of astronauts the same way to show whether the pattern holds.
The full study was published in the journal Circulation.
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