Study: Astronauts’ Hearts Stabilize After Six Months in Space, Thanks to Exercise

NASA has spent decades worrying about what happens to astronauts’ bodies in space, and a new study offers some comfort: exercise appears to protect the heart from prolonged exposure to microgravity. The research, published Tuesday in Circulation, tracked 13 astronauts who performed echocardiograms during six months in orbit, revealing how their hearts changed — and then recovered — after returning to Earth.

The finding matters because a Mars mission is on the horizon, and that journey will involve two six-month trips through microgravity, separated by 18 months on the red planet. Weightlessness is well known to weaken bones and muscles. There were concerns about how astronauts’ health and performance might be affected when they first stepped onto Mars to begin their work there.

The Imaging Test

The study used echocardiograms, ultrasound tests that create moving images of the heart, performed aboard the spacecraft itself. Astronauts were trained to operate the machines, guided remotely from Earth by technicians. The setup is a workaround for a practical problem: you cannot fly a doctor into space to run an exam.

The researchers taught astronauts how to position the probe against their sternum, rotate it by specified degrees, and capture images that met research standards. The result was a steady stream of data showing how the heart responded to living in a near-weightless environment for half a year.

What Microgravity Does to the Heart

Microgravity changes how fluids move to and from the heart. Heart chamber walls shift their shape, altering how the heart pumps blood. Exercise and strength training can offset some of those effects, according to the study.

The imaging showed mild but transient changes in the heart when moving from Earth gravity to microgravity. Those changes stabilized over the six-month period in space, and then returned to normal after the astronauts got back to Earth.

The Mars Simulation

The study also tested what happens when astronauts are exposed to simulated Martian gravity, which is roughly three-eighths of Earth’s pull. The authors credit exercise regimens for protecting the astronauts’ hearts from prolonged time in space and in a simulation of Mars-like low gravity.

“The single most novel thing that we showed was that after six months in space, when you come back down to Earth and then are exposed to three-eighths gravity, which is the gravitational gradient that we will experience on Mars, that nobody, not a single astronaut, had a cardiovascular response that was more stressed than the upright posture on Earth before they went,” Levine said. “That was really reassuring to me.”

Levine is director of the Institute for Exercise and Environmental Medicine at Texas Health Presbyterian Dallas.

The Caveat

There is a catch. The astronauts in the study were able to complete their countermeasures — the exercise routines designed to fight the effects of microgravity. When they landed on Earth, they received medical support, and some got IV infusions.

But what would happen if an astronaut got injured and could not exercise? That might be a problem, and they might be more compromised when they land.

A Career of Concern

Levine has spent his career as a top consulting cardiologist to NASA, focused on keeping astronauts healthy, especially their hearts. Now that a Mars mission is on the horizon, his research continues to test how well exercise maintains the heart’s structure and function during prolonged spaceflight.

The mission to Mars is currently planned for 2035. That timeline means NASA is already working on the equipment and protocols needed for the journey.

What Exercise Protects

Exercise protects more than the heart. In the context of the space program providing transportation to Mars, astronauts will need devices and tools to preserve the entire spectrum of human adaptation to physical activity. That includes:

1. Skeletal muscle
2. Bones
3. The brain
4. Mental status

The study’s findings suggest that exercise regimens can stabilize the heart’s structure and function during prolonged exposure to microgravity, and that the recovery process begins immediately upon return to Earth.

The Equipment Question

For the trip to Mars, the question of equipment remains open. The NASA exercise scientists are working on what will be included, though Levine noted that the balance between mass, volume, and power requirements will shape the final design.

The space station has a treadmill, a bike, and a weight system. A spacecraft bound for Mars will have less room, so the devices will need to be compact.

What Comes Next

The study provides a foundation for planning the Mars mission. It shows that the heart can adapt to microgravity with proper exercise, and that the adaptation stabilizes over time.

The findings also raise questions about what happens if an astronaut cannot complete the countermeasures. That is a concern the researchers have flagged, and it will need to be addressed before the mission launches.

The bottom line is relief. The study found that astronauts’ hearts stabilized after six months in space and recovered normally on return, thanks to exercise, easing worries about prolonged exposure to microgravity.

astronauts · heart health · microgravity · NASA · space travel