On this planet, gravity faces many fluctuations, but humans spend most of the time in 1.4-1.5 gravity. During these periods (usually lasting about 5-7 days) I was thinking I'd have them increase salt in their diet to increase blood pressure so their brain would receive sufficient oxygen. I realize that increased salt means decreased calcium which would lead to more kidney stones and risk of osteoporosis. So to counteract this, I would increase the calcium in their diet (also a risk of kidney stones if they take in too much, but hey).

My question is, what other effects would this diet have/what else should I take into account regarding the increased gravity? Would their lifespan decrease(or, for the sake of argument, increase?) Are they more prone (or less prone) to certain diseases/conditions? How would the 1.5g change other organs? Would their brain maybe distort in shape and cause mental changes? I know in 0g eyeballs can become deformed (rounder) and change the person's vision for the worse, but what would the opposite do? Would it be dangerous to give birth, even when mostly submerged in water? The people are shorter (average being 5'5 for men, 5'3 for females) and stronger than we earth beings. What would have more muscle mass entail, other than more eating? Also, would the biological difference between genders cause men to be more susceptible to certain things than women or the other way around? The day cycle is almost 29 hours on this planet, and they sleep around twelve-fourteen hours since they exert more energy. So this would give their bodies more time to recuperate, but then the question becomes would lying around for longer periods of time have detrimental effects as well? And there's a 3 day period where the gravity gradually increases from 0.4g-1.3g before eventually reaching 1.5g. I assume this is better for them as it gives them a ‘break’ and slowly reintroduces them back, but I have no idea.

To specify, my question is not how would they adapt to this environment. Assume that has already happened, I just want how their body currently works to be as accurate as possible. I'm looking for any gap in my thinking and their possible solutions. I realize there is a lot of variables and questions here, but feel free to answer just one of the hundred to help me get things in order.

First post on this site, so apologies if I've made any mistakes.

Edit: I'm aware the gravity situation is not at all accurate, I'm just looking for answers relating to human biology when placed in this circumstance.

  • $\begingroup$ Hello, Silvirs, and welcome to Worldbuilding.SE! Please take our tour and visit the help center to learn more about the way the site works. Have a nice day! $\endgroup$
    – Gryphon
    Jul 22, 2018 at 21:37
  • $\begingroup$ On this planet, gravity faces many fluctuations This just does not happen. A planet's gravitational field will not fluctuate like this. there's a 3 day period where the gravity gradually increases from 0.4g-1.3g before eventually reaching 1.5g I cannot imagine a reason why such a thing would happen. $\endgroup$ Jul 22, 2018 at 22:15
  • 2
    $\begingroup$ StephenG, you are correct, the fluctuations are not at all based on science as we know it, but a more magical element that would go off topic if I explained it. I only care about the biological aspect. $\endgroup$
    – Silvirs
    Jul 22, 2018 at 22:18
  • $\begingroup$ Magic is not off topic on WB. But mixing and matching magic and science is usually not recommended. That said note that the magic system that produces this fluctuation in gravity could be important to people answering. $\endgroup$ Jul 22, 2018 at 23:59
  • $\begingroup$ Related: worldbuilding.stackexchange.com/questions/71379/… $\endgroup$
    – cls
    Jul 23, 2018 at 4:14

2 Answers 2


Apart from chemical adaptations, the bigest problems I see are the spinal cord and knees. Even after centuries of evolution, modern humans often suffer from abrasions and damage to the cartilage in the knee joint or spinal disks.

In an environment of increased gravity, people would suffer from typical joint related old-age diseases at a younger age. Or their bodies would malform at a young age. A possible physical adaptation could be to revert to a quasi quadrupedal walk like chimpanses and gorillas. For that you would need longer arms and shorter legs, so the proportions of humans have to change quite a lot.

If they stick with the upright walk, the hips would probably become wider and stronger to offer better support for the entrails. A narrowing of the birth chanal would pose severe risks for any mother-to-be.

Edit 1

The thought of medieval corsets just came to my mind. In contrast to 18th century corsets that resulted in a wasp-waist, medieval corsets were used to support the back of hardworking people like housewives, soldiers and miners. If your people used corsets they wouldn't have to adapt too much physically.

Edit 2

Another rather funny but maybe realistic idea is to use crutches in times of high gravity and leaving them at home at times of low gravity. The regular use of cruthes would have an impact on their cultural accessoirs and behavior. Since one or both of your hands are occupied, to carry items around you need backpacks or bags with long straps that can be worn over the shoulder.

The social duties of people would differ greatly depending on their age: (abbreviations HG = High Gravity; LG = Low Gravity)

  • Infants / small children won't do much during HG but compensate by excessive playing during LG
  • Older children and juveniles are expected to carry stuff around and do most of the work during HG (since they don't suffer from abrasions in their joints yet) and have to tame the infants / small children during LG.
  • Young adults have their mid-life-crisis at 25 - 30, when they notice the first joint aches and have to contemplate using a crutch or not
  • Adults try to cope as best as they can in HG but have to get as much work done as they can in LG
  • Elderly need assistance during HG and probably avoid standing up and walking as much as possible. LG is the time when they can feel somewhat younger again and help in controlling the infants / small children.

Concerning blood flow to the brain you could take giraffes as an example. Standing tall, their hearts have to pump blood all the way to the brain, but while drinking, they have to lower their head to the water level, resulting in a dangerous rush of blood. They have a sponge-like appendage to the brain that absorbs the excess blood and keeps them from passing out or bursting blood vessels in the brain.

  • $\begingroup$ I'd like to keep them bipedal, but I really appreciate the idea of a corset-like accessory to support their backs, as well as the broadening of hips. I actually do want them to have health issues caused by the gravity, just not crippling ones, so a weakening of joints would be "good" and an interesting plot device even if it may eventually lead to actually being crippled. If you have any idea on how to either counteract or delay the stress on the joints I'd be interested in hearing it. $\endgroup$
    – Silvirs
    Jul 23, 2018 at 14:36

If you are asking about people that came from what we consider a 1G environment, they would get tired faster and potentially have swollen feet and routine lightheaded effects. They would need to be in decent physical shape to survive at length.

Compared to earth humans (if aloud to sufficiently evolve) they would have bigger hearts and slightly bigger muscles in general.

This is basically the reverse situation that astronauts have when they enter microgravity environments.


1G is a somewhat arbitrary datapoint and happens to be the force of gravity on the planet that we humans evolved on. As such our bodies have evolved to operate quite well in this environment and now that we have been going to space somewhat routinely for the past 50 or so years we have been able to observe what happens in other environments. One thing we know is that our bodies are set up such that we spend more energy pumping blood up to our brains than down to our feet. Its not that our brains need more blood (although they may) but that humans generally evolved in a upright position so the blood we pump above the heart must also fight gravity while the blood we pump to our feet can effectively flow there with the assistance of gravity.

We have observed that when humans enter a microgravity or "0G" environment their faces (and upper bodies) appear to puff up. This is a result of the fact that the heart is no longer pumping against gravity but still pumping with its same old strength. Fluids also tend to migrate towards the head for a similar reason.

If a human were routinely under a 1.5G environment their heart would need to work harder to pump the blood above it and they would experience pooling effects in the lower part of their body. This is a far less extreme version of what fighter pilots know as G-LOC.

Many of the studies out there are concerned with humans in lower G environments (space travel mostly) but this answer would indicate that 7 days at 1.5G is perfectly fine however long term effects may yet be unknown.

Other answers here suggest the possibility of using a corset like device. Much like the fainting issues that occurred in the 1700's this may not have a good outcome. The human body needs blood flow to survive and corsets work to cut that off, in the chest they can also have breathing issues. This is the basic principal on which Anti-G-Suits however those only cut off blood flow during short times of heavily increased G-Load to prevent pooling. They are essentially momentary corsets, they would not work very well in a sustained situation.


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