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Comment by Abekkus | Hacker News Reader

I had previously read that there was a point of no return for walking atrophy, somewhere before the two-year mark. Hope the medicine has improved, for this astrionaut's sake.

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I'm sure that international space programs have figured out ways to mitigate atrophy by now.

They have not. The astronauts have to exercise for hours per day (2.5 last I checked) in specially designed systems, but that doesn't even begin to compare to what we experience just existing under 1g. So they do experience substantial atrophy and are initially unable to even walk without assistance after getting back to Earth.

And if this can’t be overcome, it means any alien visitors of significant physical size after years of space travel would be rendered quivering bodies after landing on earth —that’s probably a good thing :)

More seriously it actually has really interesting implications for Mars and any other sort of low-g colonization. People who are born and live in only such an environment may simply be physically incapable of coming back to Earth in anything like a normal fashion.

Imagine trying to go to a place right now where suddenly you weighed 3x as much. In all probability, you would die without some sort of special assistance - probably of some sort of cardiovascular failure. If you're a 180lb male, it's the equivalent of strapping a 360lb weight suit on yourself, with the relevant difference that lying down wouldn't offer even the slightest of respite from the forces being imposed on your body. It also has interesting implications for sports, which are just going to be awesome in low g. An Earther would have a massive and tremendously unfair advantage against a Martian.

There's going to be some dramatic (and rapid) social, physical, and even evolutionary drift.

The Expanse (both the books and the movies) features some pretty good exploration of both the direct effects and the resulting social effects. In that universe, people who have lived in the Asteroid belt for ~3 generations can't visit earth without significant medical intervention, but their anatomy begins changing (e.g. in the younger generation some people become significantly taller). An Earther might have a significant advantage on Earth, but on Mars or in the Asteroid Belt they are stronger but less adapted in other ways.

Martians could be taller though. So in a basketball game on Mars, the Earthlings would be hopeless.

Trying to arc shots (or even move around the court) in gravity different than that you've experienced your entire life might cause more difficulty than physical differences between players, I'm thinking.

Not an issue if they have a means of propulsion capable of delivering 1g the whole way

Which is necessary to go any meaningful distance in space anyway

True mitigation would be spin-wheel sleeping and standing. Basically a centrifuge with spacesuits at the end, so they sleep/train in simulated gravity. They do not have that on the iss- although the snake-robot crane could do the job.

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