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Long-duration missions in space take a toll on the body, astronauts lose bone density and suffer muscle loss.

Both have said they enjoy the two hours or more of exercise they must do daily to combat the loss of bone density from living in space.

Long duration missions in space take a toll on the body, astronauts lose bone density and suffer muscle loss.

That's in part because on Earth, the force of gravity constantly acts on the skeleton, which stimulates bone-building cells called osteoblasts that maintain our bone density.

Without that force, bone density and muscles can atrophy and weaken, with bones becoming 1% less dense for every month spent in space without any measures performed to combat bone loss.