What effects would moving between areas of different gravity have on a human?

Question

Basically, this is a setting in which artificial gravity generation is possible and can be confined to certain areas with different settings. There are maybe five human colonies on planets with near-Earth gravity (ie close enough to 1g as to make not much difference), but there are also human colonies on worlds with less/more gravitational pull. Artificial gravity adjustment is used on these worlds to keep the areas of human habitation closer to 1g than the rest of the planet, but humans can still travel outside of these areas and into zones where the local gravity is in effect, so people are somewhat used to moving between different areas of gravity.

There are two types of artificial gravity generators. One is used for extremely large areas such as a walled in or domed city. Others are used for smaller indoor areas, such as a the interior of a building or a spaceship. The larger one has a dissipating strength - as in the closer you are to the generator the better the effect of it is (so basically if you are generating 1g on a planet with less gravity than Earth, you'd have to be closer to the central radius of the generator to actually feel 1g, with it incrementally decreasing the further away you get). The smaller one is far more evenly spaced in its gravity distribution, with very little dissipation of effect on the edges.

So my question is what would be the effects of moving rapidly from one area of gravity to another? Say a person is in a building set at 1g, but runs out into an area that is 0.7g? Or 1.3g? I'm not talking huge increments. The maximum deviation from Earth norm on the heavy end will be 1.5g, while the low end would be maybe 0.4g or 0.3g. I am also not adverse to the idea of a dial getting messed with and having an entire area made into 0g on accident.

Basically, I'm writing a chase scene. The characters are going to be transitioning between areas of different gravity. I need to know if by doing so, if there will be puking, tripping, accidental breakage of bones, bouncing, fainting, heart attacks, muscle strain, nothing, or all of the above.

Answer 1

Immediate effects:

If you are not prepared, the change in gravity might cause you to fall, just like when you don't watch where you're going and accidentally step onto an escalator or other moving patch of ground. Heavy -> light might cause you to accidentally propel yourself forward too much; light -> heavy might cause your legs to give out on you because your muscles aren't prepared for the suddenly greater strain.

Based on the assumption that going through a rollercoaster doesn't cause any immediate health concerns through the changing gravity (unless you have a weak heart etc.) I assume that changing gravity within the space of a step will not cause any health problems either. Small gravity changes (ca. 0.1g) can also be compared to an elevator starting / stopping. So you can probably expect a sinking / lifting feeling when crossing the boundary.

Short-term issues:

Until your body and brain have adjusted to the new gravity, you will misjudge what strength it takes to run / jump / throw / lift unless you concentrate on those actions.

Normal-gravity comparison: When you lift a gallon bottle, your mind and your muscles expect it to have a certain weight. However, when the bottle is empty when you expected it to be full, you might accidentally knock it on the shelf above it before your muscles compensate for the unexpectedly light weight. On the other hand, you won't be able to lift it at first when you expected it to be empty but it turns out to be full after all.

Sure, your body will compensate quickly for unexpected weights. But in a chase situation where everything depends on split-second changes I expect you will do a lot of overshooting, undershooting, etc. The body works a lot with muscle memory, and until the muscle memory has gotten the memo 'different strength needed' you will have problems when you don't concentrate.

I am not a biology expert, but I'd say it takes at least 4-5 repetitions to set the muscle memory to the new standard. So, after 4-5 steps you should have walking/running down pat in the new gravity. But when you suddenly decide to throw in a pacours wall-jump you'll probably have to do a lot of on-the-fly correcting and landing in unexpected positions. After 4-5 pacours wall-jumps, you'll probably have that one down as well. But then you might decide to do some other acrobatics. The adjustment period will get quicker since you are constantly gathering experience (2-3 tries instead of 4-5). But it will take time and practice to completely get used to the new gravity in that regard (I'd expect somewhere between 30min and several hours).

Longterm issues:

Since you are writing a chase scene, the longterm issues are pretty moot. Medium long-term: just like some people can't adjust to living in high altitudes, there might be people who can't adjust to living in a different gravity. Really long-term: I'm thinking of growing up in low-G and then going to a high-G environment. Gravity affects things like bone density and muscle tonus (not only of the trainable muscles like biceps but also of intestinal muscles etc.), so I'd expect a lot of potential problems coming that way. (Just imagine how many problems Astronauts have coming back to earth after a stint on the ISS, and that is despite being there for less than a year and having a special training schedule to not lose their earth-G muscles).

Multiple gravity changes in short time issues:

Going with the rollercoaster example as quickly changing gravity, I imagine you might get a headache or an upset stomach from multiple rapid changes. If you have any pre-existing medical conditions, they might be exacerbated.

That aside, the longer the chase lasts, the more likely it becomes that one of the characters loses concentration and misjudges something in varyingly fatal or at least chase-ending ways. The quicker you change gravity, the less you can benefit from adjusting muscle memory, and the more you need to concentrate on every single step or motion.

I think it is possible to train for that, so that you know what to watch for when entering a new gravity at a full run. So someone trained might have an advantage over someone untrained. But unless gravity-caused medical issues come into play, it will come down to who does multi-tasking better (concentrating on running in new gravity + (chasing perpetrator or escaping chaser)).

Bonus effects:

When you are changing the direction of gravity (i.e. floor and ceiling suddenly becoming walls, and the walls becoming the new floor) you will probably have to deal with a lot of disorientation. And nausea.

Answer 2

One of the first things that people who experience zero gravity for the first time do is start swimming. During the "making of" video for the OK GO film clip for Upside Down Inside Out they recently released, where they filmed inside a reduced-gravity aircraft (a "vomit comet"), they all observed that the first thing they did when exposed to zero G was flail around like idiots trying to swim around, as if they were dropped in water. Unfortunately, as the air around them provided very little resistance, they generally just flailed around in place.

Definite puking. The feeling of zero gravity really messes up your sense of balance and your body responds to that by think it has been poisoned, and ejecting stomach contents. Again to use that video as an example, there were nearly 60 instances of vomiting during the filming.

Heart attacks would be very unlikely, as reducing gravity would take stress off someone's heart in the short term. Muscle strain would be unlikely as well because it's easier to propel your limbs when they don't weigh anything. Breaking bones would be possible if they lose control of themselves and carom into things. Going weightless results in the equilibration of bloodflow around the body, and as such would not make anyone faint.

Long term effects of zero gravity tend to be things like muscle atrophy and related heart problems, as well as loss of bone density, but these take months to years to manifest. Your eyes also change shape after a long period of time in zero gravity, but will return to normal when exposed to regular gravity within days to a week.

Note that these things really only apply to people who aren't used to zero gravity. If you have experienced operators, they will be able to switch between different gravity areas quickly. Dropping the gravity from 1.0 to 0.2G, for example, would make people go from running normally to bouncing around like they did on videos from the moon landings, except they would not have more than 100 pounds of suit attached to them and could get even higher with their jumps.

Answer 3

I think Susanne's answer has covered most of it.

The human body is actually able to cope with a wide range of gravity already, as can be seen in any number of fairground rides where huge numbers of humans experience increased or reduced gravity with few injuries or bad effects.

Living long term in altered conditions has much more profound consequences but if you spend most of your time at 1G and then occasionally venture out I would not expect any serious problems. Movement in different gravity would take some time to get used to, especially moving in variable gravitational fields. That would be a learned skill in of itself and I'd expect it to take more than 4 or 5 steps.

In fact that's an area where someone used to the effects could have a huge advantage, if they were moving through areas where the gravity changed frequently. The native would adapt without thinking while someone not used to the effects would need to adapt each time it changed, and then as soon as they learned to run the gravity would change once more and they would be stumbling along again.