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Extended Space Travel Causes an Inevitable Drop in Physical Fitness

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Another day, another study showing how awful microgravity is to the human body. In the latest research, scientists have found that long term exposure to space inhibits the movement of oxygen through the body, reducing an astronaut’s ability to perform strenuous tasks.

New research from Kansas State University shows that prolonged exposure to space reduces an astronaut’s exercise capacity by 30 to 50 percent. That’s...a lot. As noted in the study, which you can check out at the Journal of Applied Physiology, this seems to be happening because our heart and small blood vessels suck at transporting oxygen to working muscles under microgravity conditions. Discouragingly, the effect still matters when astronauts try to maintain a high degree of fitness in space, by riding stationary bikes and running on treadmills.

For the study, a research team led by kinesiologist Carl Ade looked at NASA data collected for nine male and female astronauts who spent around six months aboard the International Space Station. Prior to embarking on their missions, each astronaut had various health measures taken to assess their physical fitness, including oxygen uptake, cardiac output, and hemoglobin concentration and saturation. (Hemoglobin is the iron-rich protein responsible for transporting oxygen in your blood.) These measures show how effective a person’s heart and blood vessels are at getting oxygen to muscle mitochondria—the so-called powerhouses of our cells.


While in space, each astronaut followed an aerobic and resistance training regimen designed by NASA. Moderate and high-intensity aerobic exercise on a bicycle or treadmill was prescribed for four to six days each week, while upper and lower-body resistance training was prescribed six days per week.

Two days after the astronauts returned to Earth, each of them were put through the same battery of physical tests they received prior to launch.


Armed with this before-and-after data, Ade was able to show a 30 to 50 percent decrease in maximal oxygen, which is the maximum rate of oxygen that’s consumed during exercise, and a standard measure of cardiorespiratory health. After about 90 days, the astronauts’ level of fitness returned above 97 percent of what it was before. Their inability to get back to full fitness capacity is likely due to altered function of the lungs following prolonged exposure to microgravity.


“It is a dramatic decrease,” said Ade in a release. “When your cardiovascular function decreases, your aerobic exercise capacity goes down. You can’t perform physically challenging activities anymore. While earlier studies suggest that this happens because of changes in heart function, our data suggests that there are some things happening at the level of the heart, but also at the level of the microcirculation within capillaries.”

The researchers suspect that microgravity is changing the way blood vessel capillaries interact with red blood cells, but more research is required to suss this out.


For would-be space travellers and Martian colonists, this news undoubtedly sucks. It means that astronauts, after several months of exposure to microgravity, can expect a fairly significant decrease in their ability to perform strenuous tasks. Once on Mars (or other celestial body of choice), an astronaut might be less capable of, say, performing manual labor on the surface. On the plus side, however, this finding alerts scientists to the problem, and they can now go about trying to figure out a solution.

“This decrease is related to not only health, but performance,” Ade said. “If we can understand why maximal oxygen uptake is going down, that allows us to come up with targeted interventions, whether that be exercise or pharmacological interventions. This important new information can help these astronauts and prevent any adverse performance changes in their job.”


We can now add reduced oxygen uptake to our ongoing list of crappy things that happen to our bodies when exposed to space—problems ranging from loss of bone density and muscle mass through to heart, vision, and back problems. Adapting humans to life beyond Earth, as we’re learning, is going to be tough.


[Journal of Applied Physiology]