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 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 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.) 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.
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