The world watched last night as two NASA astronauts emerged from their space capsule off the coast of Florida after nine uncertain months in space.
Sunita Williams, 59, smiled and waved as she was lifted out of the SpaceX Dragon craft and helped into a stretcher, assuring the public she was well.
But health experts picked up on a small detail that revealed the silent health battle she now faces.
After waving, her right arm suddenly went limp and flopped against her thighs as if they were much heavier — the result of spending so long in zero gravity.
Doctors who viewed the footage told DailyMail.com that the movement may be a sign of muscle wasting while in space for 286 days.
In the microgravity of space, muscles get smaller because the body doesn’t need to work as hard to maintain posture.
Her heart may also have shrunk because the body doesn’t need to exert much energy to allow blood to flow.
But the the fact she was still able to lift her arm in the first place was a good sign, doctors say.
It comes after other experts raised concerns over Williams’ health pointing to her thin wrists, which they said may also indicate weight loss and muscle wasting.
Dr. Stanton Gerson, who researches the impact of deep space on cells, noted that Williams appeared much more frail than her male crew member, Butch Wilmore.
‘She had more trouble, if you will, than did the other astronaut with standing up,’ he told this website.
‘This may be because it is really hard to maintain muscle mass in space without the help of gravity.
‘In space, there isn’t a differential on muscle mass, because there isn’t the stress and strain from gravity and, as a result, from undertaking exercise.
‘That means that when you do push and pull exercises, these don’t exert the same level of muscle activation as they would on Earth.’
In microgravity, muscles experience significantly less resistance, leading them to atrophy over time.
On Earth, gravity constantly forces muscles — especially those in the legs, back and core — to work against it, creating a mechanical load that prevents wasting.
Astronaut Williams waves to the camera after being pulled from her space craft
Her arm instantly flops and goes limp
The doctor also pointed out Williams would have been exhausted after her trip home.
It takes about eight hours for astronauts to pack and do pre-flight checks on the space station, and then another 17 hours for them to undock and fly back to Earth.
He said: ‘What I see is a happy, tired, astronaut. Think how you would feel after a long trans-Atlantic flight.’
Asked how much muscle mass the astronauts may have lost in space, he said that this was likely to be in the single digits and ‘minimal’ — based on his experience with previous missions.
‘It would be in single digits in terms of percentage muscle mass, and we have even had some cases — very few — where astronauts have come back with a little extra muscle mass,’ he added.
Men have more muscle mass than women, overall, which can lead to women being more seriously affected by the loss of a small amount of muscle mass.
On the return to Earth, he said astronauts may have appeared unsteady because of the impact of the planet’s gravity on their inner ear.
‘It turns out that our inner ear has evolved very, very, well for the environment here on Earth,’ he said.
‘But in space, because of the lack of gravity, we lose some of the fluid in the inner ear which causes it to start behaving differently.
‘When we come back, this can cause vertigo,’ which is a sensation of spinning, whirling or moving when you are not actually in motion.
It always takes time for astronauts to recover after returning to the US from space, with experts saying this can take a month to three months.
But there have been no recorded cases of astronauts suffering from permanent health problems as a result of being in space.
Dr Vin Gupta, an Air Force surgeon who works with people who spend a long time in the air, added that it was a good sign she could still lift up her arm.
‘Anyone who is able to elevate their arm is then also able to lower their arm successfully, should be OK,’ he said.
Studies have shown that other health effects of being in space for long periods include the brain shrinking and swelling in the eyes, which happens because the lack of gravity causes the positioning of fluids to shift.
Dr Stanton said patients recover quickly after returning to Earth with no long-term adverse health effects.
He said some astronauts have reported ‘brain fog’ after returning to Earth, but that this clears within a few days to weeks.
