Human bodies are made to live on Earth, so strange things happen to astronauts’ bodies when they spend long periods in outer space, Dr. Christopher Kain, an orthopedic and spinal surgeon, told visitors to the Cosmosphere on Saturday.
Without gravity to compress his spine, NASA astronaut Scott Kelly grew 2 inches during his nearly yearlong stay on the International Space Station, although that wasn’t a change that lasted long, Kain said.
“Within a week, he was his normal height,” he said.
Some other effects of weightlessness are reversible, but take quite a bit longer. Kain said astronauts lose about 20 percent of their muscle mass in as little as 11 days in space, because they don’t have to push against gravity.
A loss of bone density and strength during prolonged spaceflight takes even longer to reverse, Kain said. Physical stress – whether lifting things or the impact of every step a person walks – makes bones denser and stronger, he said, and a weightless environment robs bones of a lot of that workout.
“Your bone melts like butter in a frying pan” in weightlessness, Kain said.
He said astronauts can get their bone mass back over three to five years with a lot of work and treatment.
Other issues caused by weightlessness include a person’s heart getting weaker and face swelling, Kain said, both because the human body normally has to pump blood against the force of gravity.
“Nothing good, over time, happens in a weightless environment,” he said.
How to cope with those issues is one of the major challenges with the prospect of sending astronauts to Mars, Kain said.
Kain said willingness to accept these health risks in the name of science and exploration is part of astronauts’ heroism.