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Effect of Microgravity on Bones

Author: Suhani Patel

Editors: Galiba Anjum and Kira Tian

The human body has evolved within the constant pull of Earth’s gravity. In the microgravity environment inside the orbiting International Space Station, bones and muscles don’t have to support the body’s mass (weight on Earth). Without Earth-like exercise, astronauts would experience bone and muscle loss—scientifically known as atrophy—while working in space. Since bone and muscle atrophy is not unique to space environments (it also occurs from normal aging, sedentary lifestyles, and illnesses), it can cause serious health issues from injuries due to falls or osteoporosis for both astronauts and individuals on Earth.

NASA researchers have been working on understanding the mechanisms causing microgravity-induced muscle and bone atrophy and how to prevent it from happening in order for astronauts to remain healthy during missions as well as when they return to Earth or set foot on the Moon and, in the future, Mars. Since astronauts need to maintain strength in order to carry out research while also standing and moving without gravity, it’s important that we figure out the mechanisms behind atrophy. A nutritious and adequate diet alongside proper exercise is essential to maintaining individuals’ health. A diet deficient in nutrients or calories can increase bone and muscle atrophy, while a well-balanced diet with the appropriate vitamins and minerals can help prevent it. In addition, astronauts working aboard the space station are “prescribed” more than two hours of exercise per day to combat muscle and bone atrophy. Research continues to help determine the right combination of diet, exercise, and medication to protect against bone loss.

Exercise is important for keeping the musculoskeletal system—the muscle and bone system—strong and to prevent bone and muscle loss. Research done on Earth and on the space station has demonstrated that high-intensity resistance workouts are the most effective way to reduce bone and muscle loss. The Advanced Resistive Exercise Device (ARED) on the space station allows astronauts to perform high-intensity workouts.

While researchers understand the general causes of bone and muscle loss, they continue to investigate fundamental mechanisms and other specific contributing factors; research done in space of the effects of microgravity on bones and muscles is an important part of these efforts. For example, some research assesses the likelihood of bone fracture following exposure to microgravity by scanning the hip bones of astronauts. There are also studies that compare subjects on the ground to those aboard the station or in simulated conditions of spaceflight.

The search for bone atrophy treatments in space overlaps with research on bone loss associated with osteoporosis on Earth. While in space, immobilization and illnesses occur at a much higher rate than normal aging; however, both conditions happen due to bone resorption occurring faster than the formation of new bones. This means that optimizing exercise regimens and developing drugs to treat bone loss benefit people on Earth while also providing countermeasures for people on space missions. Drugs that prevent bone turnover have successfully prevented bone atrophy in both astronauts and animal models in space.

While space station research helps us understand how to prevent and treat muscle atrophy and bone loss, optimizing countermeasures for astronauts is particularly important because NASA is planning missions to the Moon as well as Mars. While in those partial-gravity environments, astronauts need to perform strenuous activities after a long time in near weightlessness. And thus, we need additional research aboard the space station in order to develop the best countermeasure protocols for space travelers as well as to advance treatments for people on Earth.



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