The Subregional Bone Assessment, a NASA study of the long-term effects of microgravity on the bones of International Space Station crewmembers, showed that the astronauts lost roughly 11% of their total hipbone mass over the course of their mission, more than an elderly woman in a year. While bone mass was regained after a year on Earth, bone structure and density had not recovered. The research focused on weight bearing bones including the hip, which experiences the highest amount of bone loss during a space mission and is the site of the most fractures in the elderly.

One of the first the Human Research Program investigations, similar human health experiments have been done to understand and reduce health and performance risks to astronauts in space. The research aims to predict and address health issues facing astronauts during long-term missions on the Moon, to Mars, or on other microgravity missions.

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