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I know the human body can survive multiple g's for short periods - like fighter pilots or F1 drivers. But what is maximum survivable gravity for more than just a transient moment? Could a body live on a 1.5g planet for 8 months or would their circulatory system shut down? Would something as simple as compression garments help? I remember reading JBS Haldane "On Being the Right Size" in junior high but can't recall the conclusions.

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  • $\begingroup$ worldbuilding.stackexchange.com/q/37195/30492 $\endgroup$
    – L.Dutch
    Commented Jun 12 at 15:40
  • $\begingroup$ @L.Dutch I've looked through the various related questions, and none of them have convincing answers. Its all just guesswork and handwaving. A new user trying to prompt for new answers on old questions is largely impractical, too. $\endgroup$ Commented Jun 12 at 15:48
  • $\begingroup$ Will the humans have training beforehand/time to acclimate to high g? Also, are they spending the time walking around and living like normal, or strapped to a special chair? These would make a pretty big difference. $\endgroup$
    – Bubbles
    Commented Jun 12 at 19:48

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Your main problem here is that no-one really knows... that's why all of the questions and answers linked in the "related" section on the right aren't all that helpful. The experiments simply haven't been done, and the equipment to do them hasn't been built.

That said, this quote from The Human Centrifuge might be of interest:

What should the gravity level be? This is a difficult question. To answer this we could, as a first approach, rely on extrapolating data from long duration animal studies or short duration human experiments. From a very comprehensive study by Wunder et al. (1963) we could extrapolate a maximum value around 1.5 to 1.8×g. The limiting factor might be the body fluid balance (personal comment Dr. R. Burton). Bone and muscle systems are used to high loading although these peak loads are of short durations. Without a large radius centrifuge it is difficult to answer this question, however.

(I've not found an online copy of the referenced Wunder paper, Survival and growth of organisms during life-long exposure to high gravity)

Van Loon was asking a slightly different question to you, however... he was interested in things like building up astronaut muscle mass and bone density prior to long term microgravity exposure. That means that the people undergoing this experiment/training program would be expected to be in there for a fixed period of time though that period wasn't stated. It does seem like a reasonably good starting point, however.

From The Biology of Human Survival: Life and Death in Extreme Environments (pdf link):

Human volunteers have tolerated 1.5 G for seven days with no apparent ill effects. However, after just twenty-four hours at 2 G, evidence of significant fluid imbalance is detectable. At 3 G to 4 G fatigue is limiting, and above 4 G cardiovascular factors limit G tolerance.

The author does not reference the study here, so I can't find any further details. Many people reference this quote, but none of them seem to cite an underlying study either, which seems a little suspicious. I found one reference to a 24 centrifuge stay at 2 G (The G Machine, Smithsonian magazine) but no mention of physiological issues. Maybe you'll have better luck tracking down the original source.

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  • $\begingroup$ One can draw charts and graphs and analyze and speculate endlessly, but as the old saying goes, an ounce of experiment is worth a pound of theory. And to the best of my knowledge, no one has ever done the experiment, because it's very difficult to construct such an experiment on Earth. I read years ago of an experiment where they put people in a room rotating at high speeds for a long period, but that added the problem of centrifugal forces complicating things. (I don't have a citation for the experiment. I'll have to look for it.) $\endgroup$
    – Jay
    Commented Jun 13 at 15:57
  • $\begingroup$ @Jay ...why are you summarizing my answer back to me? $\endgroup$ Commented Jun 13 at 16:19
  • $\begingroup$ I mean, the second sentence is about the experiments having not been done, and the last paragraph is about an experiment people talk about but can't actually cite :-/ $\endgroup$ Commented Jun 13 at 16:20
  • $\begingroup$ You're going to attack me for agreeing with you? Umm ... ok. $\endgroup$
    – Jay
    Commented Jun 15 at 1:57
  • $\begingroup$ @Jay I’m not attacking you… I’m just puzzled. $\endgroup$ Commented Jun 15 at 7:14
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Human tolerence for high gravity was discussed in Habitable Planets for Man (1964) by Stephen H. Dole, on pages 11-13.

https://www.rand.org/content/dam/rand/pubs/commercial_books/2007/RAND_CB179-1.pdf

Discussing the evidence from research up to then, Dole concluded on page 12 that:

Based on the available evidence, one might conclude that few people would choose to live on a planet where the surface gravity was greater than 1.25 or 1.5 g.

The revised second edition in 2007 might contain results of later experiments in high gravity tolerance.

And I guess that few people would want to live on a planet with surface gravit greater than 1.25 or 1.5 g.

If it turns out that 1.25 g is the maximum surface gravity for people to want to live on a planet full time, people who are resistent to the bad effects from high gravity could voluteer to go to a planet with a surface gravity of 1.5 g for a period as long as 8 months.

And if a surface gravity as high as 1.5 g is the maximum that people would want to live the rest of their lives under, they would be even more willing to spend only 8 months on a world with a surface gravity of 1.5 g.

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  • $\begingroup$ One thing to consider, all those studies were conducted on healthy adults in their prime. My uneducated guess is that the increased gravity would have significantly worse effect on the elderly, or really anyone past their prime, and unpredictable but likely dangerous effect on children and babies. Fetuses in utero surviving in anything significantly more than 1g is likely out of question. $\endgroup$ Commented Jun 13 at 7:19

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