Astronauts may be able to arrive on Mars with hearts strong enough to handle the planet’s gravity after months in space if they keep exercising along the way.
A study co-led by a UT Southwestern Medical Center researcher found that cardiac changes during roughly six months in microgravity were largely transient and that astronauts’ hearts remained within a range researchers say should be adequate for Mars’ lower-gravity environment.
The findings were recently published in Circulation and shared Wednesday by UT Southwestern.
“Our previous studies had demonstrated that the heart atrophies in both bed rest and in space — it becomes smaller and stiffer — and we were concerned that could be a problem over long-duration spaceflight, especially for missions to Mars,” said Dr. Benjamin Levine, professor of internal medicine at UT Southwestern.
“Our findings suggest that the exercise countermeasures we already have in place are enough to keep the heart in good working order for Mars’ gravitational loads,” Levine said.
What Happens To The Heart In Space?
Human hearts evolved to work under Earth’s gravity.
In space, the cardiovascular system no longer has to pump blood against the same gravitational forces, and the body begins adapting.
NASA identifies cardiovascular adaptation as a significant concern for long-duration missions. Low gravity and other spaceflight stresses can alter the heart and blood vessels and potentially contribute to low blood pressure after landing, abnormal heart rhythms, blood clots, and other cardiovascular problems.
Those risks become increasingly important as NASA looks toward missions lasting months or years.
Levine, who is also founding director of the Institute for Exercise and Environmental Medicine at Texas Health Presbyterian Hospital Dallas, has spent years studying how the cardiovascular system responds to unusual gravitational environments.
Researchers Followed Astronauts During Six-Month Missions
UT Southwestern said researchers worked with 14 astronauts (nine men and five women) who spent about six months aboard the International Space Station, roughly the duration researchers use when discussing a possible transit to Mars.
The peer-reviewed study reports that 13 astronauts, nine of them men, were included in the final analysis, with a median spaceflight duration of 164 days.
Before launch, the astronauts underwent echocardiograms with Doppler ultrasound while exposed to several body positions designed to represent different gravitational loads.
Researchers measured them lying flat, at a 22-degree tilt designed to simulate Mars’ roughly 0.38 G environment, and sitting upright to represent conditions closer to Earth gravity.
Once aboard the International Space Station, astronauts trained in echocardiography performed additional scans at approximately days 14, 30, 75, and 135 and again roughly 15 days before returning to Earth.
That allowed researchers to observe how the heart changed during the mission rather than comparing only preflight and postflight measurements.
Hearts Became Smaller Early In Flight
During the first two weeks in space, researchers found reductions in measurements including left ventricular end-diastolic volume, stroke volume, and measures of myocardial deformation.
In simpler terms, the heart became somewhat smaller and pumped less blood per beat early in the mission.
UT Southwestern reported that all of the astronauts experienced some changes in cardiac structure and function during that period, with their hearts shrinking slightly.
Levine said the early changes were not surprising because astronauts often experience motion sickness and are adjusting to mission duties during the first days of spaceflight, which can limit exercise.
But the changes did not continue worsening.
As the missions progressed, left ventricular volume and stroke volume increased toward preflight values, according to the study.
Exercise Appears To Be The Key
Astronauts began exercise programs as soon as they were able after reaching the space station.
The specific routines described by UT Southwestern lasted about 45 minutes to one hour per day and included endurance and strength-building exercises.
NASA’s broader International Space Station exercise program is more extensive. Crew members currently average about two hours of exercise each day, using equipment including a treadmill, stationary cycle, and the Advanced Resistive Exercise Device, which mimics weightlifting in microgravity. NASA says the regimen is designed to counter losses in muscle and bone as well as cardiovascular deconditioning.
As the astronauts continued exercising, the early cardiac changes gradually moved back toward their preflight measurements.
The published study concluded that, with current countermeasures, spaceflight lasting up to six months did not produce large changes in cardiac structure or function beyond the range associated with normal changes in posture on Earth.
Could Astronauts Function After Landing On Mars?
That is the question that makes the study particularly relevant to future Mars missions.
An astronaut traveling to Mars would not simply spend months in microgravity and return directly to Earth. Crew members would have to land on another planet and begin functioning under gravity again.
Within a day after returning to Earth, participants underwent additional echocardiograms under simulated zero-gravity and Mars-gravity conditions.
Researchers found that after approximately six months in space, the astronauts showed no greater cardiac volume or hemodynamic stress under simulated Martian gravity than they had experienced while standing upright on Earth before flight.
The authors said the findings suggest orthostatic intolerance — difficulty maintaining blood pressure when upright — may be unlikely on Mars after a six-month transit when astronauts use appropriate exercise countermeasures.
That does not mean a Mars mission would be free of cardiovascular risk.
The study was small and exploratory, and the astronauts were living aboard the International Space Station rather than traveling through deep space. A real Mars mission would involve additional concerns including radiation exposure, isolation, communication delays, limited medical resources, and potentially much longer total mission durations.
NASA continues to classify cardiovascular changes as a health risk for extended missions and is studying ways to protect astronauts as trips extend farther from Earth.
Mars Research Is Accelerating
NASA has increasingly used both the International Space Station and Earth-based analog missions to study how the human body may respond to longer journeys.
As previously reported by The Dallas Express, NASA is recruiting volunteers for a yearlong Moon and Mars Exploration Analog mission scheduled to begin no earlier than August 2027 at Johnson Space Center in Houston. The study will examine how participants adapt to isolation, confinement, and other demands associated with deep-space missions.
NASA has also continued studying how much exercise equipment future crews will actually need.
Deep-space spacecraft are expected to have far less room than the International Space Station, making large treadmills and other exercise equipment harder to accommodate. NASA’s Zero T2 study is examining whether astronauts can maintain health on long missions without using a treadmill at all.
Findings Could Help Patients On Earth
The Dallas-led research may also have applications closer to home.
Levine and his colleagues have studied patients with disorders involving difficulty tolerating gravity, including fainting, orthostatic intolerance, and postural orthostatic tachycardia syndrome, commonly known as POTS.
UT Southwestern said similar endurance and strength-training programs have previously improved symptoms among some patients with these conditions. Researchers hope the astronaut findings could lead to a better understanding of how cardiovascular systems respond to gravity and potentially inform treatments on Earth.
