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In micro-gravity and zero G, people's muscles deteriorate. If you sent a set of already very physically fit soldiers to train/live on a high gravity planet, would they perform better than other soldiers when they returned to zero G or normal gravity?

Basically, could you make super-soldiers by sending a bunch of regular soldiers to live on a heavy planet for awhile, so when they come back the higher muscle and bone strength could serve as a significant combat advantage?

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  • $\begingroup$ Welcome to Worldbuilding.SE! We're glad you could join us! When you have a moment, please click here to learn more about our culture and take our tour. Keep in mind that muscle strength is only part of the problem - what gravity does to bones, the cardiovascular system, cartilege (I'm sure I mispeled that :-)) your foot arch... this all contibutes. In other words, the super strength might be balanced by weaknesses (making your story realistic). $\endgroup$ – JBH Oct 5 '18 at 0:10
  • $\begingroup$ I would recommend reading the answers to the related questions on this page - particuliarly this one. Though this question is not a direct duplicate, and thereby no direct answer, the answers on them are highly related (pay particular attention to what high Gs do to fluid and bones in the body). $\endgroup$ – JGreenwell Oct 5 '18 at 1:00
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    $\begingroup$ You don't make soldiers from Marines!!! $\endgroup$ – RonJohn Oct 5 '18 at 1:04
  • $\begingroup$ I think it might be more easily done on Earth - increase the weights they have to lift in a gym, increase the resistance on their exercise bikes, increase the weight they carry while running / climbing, etc. This would all probably have the same effect but much more cheaply and it would be much easier to tailor to specific soldiers and find the optimum levels. $\endgroup$ – colmde Oct 5 '18 at 10:58
  • $\begingroup$ Related (not dupe): worldbuilding.stackexchange.com/q/48638/21222 $\endgroup$ – Renan Oct 6 '18 at 12:06
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I don't think so. The biggest issue I see is that your super soldiers are going to need to adapt to the new gravity where they are being deployed. If that gravity is different, they need to get used to it. So you might be physically stronger, but your aim is going to be different, your equipment feels different and your actions are going to be different from what your use to.

This sort of change can be deadly in combat and your soldier is going to miss vital moments because of it. For example, lets say the soldier hears a noise behind him. He turns around and gets ready to shoot. Except he has got way to much strength in his legs. He over spins, can't accurately point his gun at the enemy and gets shot.

It's all going to boil down to muscle memory. His use to a certain gravity and his muscles are going to react based on that gravity. Your instincts kick in faster than you can think, so by the time he realizes his overshot, he already has and that fraction of a second can spell life or death.

This is also going to be combined with your super soldiers deteriorating muscles. Once his in a lower gravity level, there are going to be a bunch of muscles that will deteriorate since they are no longer needed. So while this is happening, your soldier is going to need to constantly adapt to his new body until it stabilizes.

A Higher G could help in building up that additional muscle mass initially, to a safe level that your soldier can maintain it in every day life, but pushing beyond that is going to come with downsides.

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    $\begingroup$ I was going to say, well the soldier could jump, and his jump will be much higher than an average Joe, but then I realized we got bullets so.... we have a high jumping dead soldier eh? $\endgroup$ – Mr.J Oct 5 '18 at 7:51
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    $\begingroup$ Reminds me of a chapter in the Expanse book series where some people without training get hold of power armour and keep accidentally slamming themselves into walls. $\endgroup$ – Joe Bloggs Oct 5 '18 at 8:10
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    $\begingroup$ Similarly, in the Halo novels the original power armor tests go horribly wrong when a soldier tries to salute and bashes his head and consequently dies from conclusions that keep damaging himself. $\endgroup$ – Unassuming Guy Oct 5 '18 at 15:59
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    $\begingroup$ Perfect answer. Now start thinking about the differences between leaping to your feet, throwing yourself to the ground, recovering from tripping while moving over rough ground--these will all change, and could make deadly differences. $\endgroup$ – Hosch250 Oct 5 '18 at 17:56
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The simple answer is yes, but there are complications (that is, the answer is not really simple).

Yes, living at higher g will cause greater muscle development. But. There are a few problems.

Most importantly, at any sort of increased g you'll start getting injuries. Lots of them. For instance, we take our ability to balance and walk upright for granted, but it's a pretty precarious situation, and typically takes a couple of years to learn. With greater weight faster reaction times are needed to stay up, and there is only a fixed reaction time built into the nervous system. To get a feel for this, get a backpack and add your body weight to it. Put on the pack and start running around. This is a sort-of-decent-but-not-really first-order simulation of walking around in 2 gs. You'll have to be careful about how you move, or you'll fall over. Worse, in an actual 2g field, you'll fall faster than you do in 1 g, so the situation actually underestimates the reaction time problem. Since you fall faster, you'll have less time to get your hands in position to break your fall, and you'll get injured more, too.

But let's say that you've got a bunch of survivors back from high-g training. What next? Conditioning requires constant reinforcement - unused muscles quickly lose strength. Operating for any length of time in a lower-g environment will cause them to revert to just the strength they need to do operate in the current environment.

Another problem is that muscles are only part of the body system. In addition to the nervous system, there are joints and (a particularly knotty problem) the spine. I suggest you look into the issue the US Army is having with musculo-skeletal problems in troops in Iraq and Afghanistan. Carrying heavy loads on a long-term basis is bad for you. Long-term (as in lifetime) conditioning seems to help, but it takes a long time to build up all the parts that need beefing up.

And even then, there are limits. I've a friend whose son gained a lot of weight. As in he was up to 400 lb+. Eventually he decided to lose it, which everyone applauded. Problem is, his knees are in bad shape due to the load his weight imposed, and it's extremely painful for him to walk around - and running is out of the question. As you can imagine, this makes it extremely difficult for him to burn the calories needed to take off the fat. So that's another issue to consider.

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Please recall that weight and mass are two different things.

Although things may weigh more on a high-G planet, they have the same mass.

Mass is all about inertia. How much force it takes to give an object a specified acceleration (or, when stopping it, a deceleration).

It is exactly the same, on any planet (or even in space), no matter what the G, or the weight, for the same object.

To give an object with a mass of one kilogram an increased velocity of of one meter per second in one second, (an acceleration of one meter per second per second) takes exactly the same force no matter how high or low the G forces, and no matter what its 'weight'.

The same goes for stopping an object. A one kilogram object takes exactly the same force to bring it to a stop from a given speed, in a given time, no matter what its 'weight' (or the G forces of the planet).

What differs from one G-force planet to another different G-force planet, is the force necessary to get it to a certain height and keep it there. Lifting it against gravity, in other words. That is the only time you are competing against gravity.

On a perfectly frictionless horizontal (to gravity) surface, strong enough to resist gravity (hold the weight), it takes exactly the same force to move an object, irregardless of the gravitational force. However, if you are carrying the load, holding it up against gravity, it will take more energy to hold it up. That is, you need more strength to hold it up, and to lift it, but not to move it horizontally.

So your soldiers would not just have a physical adjustment to make, they would have a psychological adjustment to make. They would have to re-learn how to do every physical task. In order to accomplish the same objective, on a lower G planet, they have to move slower and on a high-G planet, they have to move faster.

That is, when the soldiers return to a lower-G planet, they would have to slow down in order to successfully accomplish the same tasks.

This is perhaps counter intuitive to normal human thinking.

So would they have a combat advantage? Not necessarily. Depends on how well their mind could adapt and transfer the skills. But certainly, a combat soldier equal in strength that is used to and trained in the gravity of a planet would definitely have an advantage over a soldier equal in strength, but trained on a higher-G planet, at least in the short term.

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No, because:

  1. The extra force in high-G will more quickly deteriorate joints like ankles and knees, and the vertebrae will get squashed.
  2. The high-G planet will also have a higher-density atmosphere which your soldiers will become acclimated to. When they return to the lower-G planet, it will be as if they're operating in the thin air of a high mountain.
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  • $\begingroup$ Your first point (very important) is correct, but the second is not automatically the case. That is the density of the atmosphere (at the surface) need not be larger or smaller - there's no direct correlation. It depends on the extent of the atmosphere. A high-G world could even have no atmosphere at all. It might have a very thin atmosphere or very thick. $\endgroup$ – StephenG Oct 5 '18 at 3:13
  • $\begingroup$ @StephenG if that high-mass (that is, after all, what makes it high-G) has an atmosphere, then it's going to be dense near the surface because, well, gravity. As for saying that a high-G planet might not have an atmosphere... that's not realistic: even the Moon has an atmosphere (it's just vanishingly thin and doesn't extend far off the surface). $\endgroup$ – RonJohn Oct 5 '18 at 3:34
  • $\begingroup$ @RonJohn Check Venus atmosphere: Venus has (more or less) the same size and mass, but it's atmosphere it's about 90 times denser. For a Venusian the Earth would have virtually no atmosphere to breath, it's like Mars for us $\endgroup$ – Pablo Lozano Oct 5 '18 at 11:11
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It would work, within limits

It would more or less do for your muscle strength what altitude training does for your oxygenation, ie give a noticeable boost.

Like others have said it would put an extra strain on your joints, however you wouldn't go to a place with 2g any more than people who do altitude training go to the stratosphere. In stead you would go to a place where you have something like 1.15g and accept the increased deterioration of joints and vertebrae as a trade off.

If this will result in "super soldiers" or in "soldiers that are stronger than they would have been otherwise" depends on your definition, but I would say it's definitely feasible as a training method.

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