Well, I don't know if I should post this question on Worldbuilding, Engineering or Game Design stackexchange, but it has been a matter that keeps hammering my brain.
In this story, armies started using full-body rigid suit ballistic armour, the type of armour that protects every centimetre of one's body. It is not a thing they wanted to do, but a thing they needed to do. After all, humans became a space faring species and their military suits must be mass produced and prepared for every kind of environment, from the vacuum of space to the high pressure atmospheres of planets.
It doesn't matter (much) of what these suits are made of (because different materials have different properties, density and weight), but you could assume that these are made of some kind of steel or ceramic composite. How the user keeps these joints from clogging and/or breaking is another problem for the me of the future.
However, the detail that I cannot escaped/solve in any way, shape or form are the shoulders.
I tried to go look for real world examples, like space suits and dive suits, but both have only in mind the fact that astronauts and divers only do repairs and tests in the environments they were built for.
For obvious reasons, these aren't made to let the user crawl on the ground and partially look up during a gun fight. I can imagine that the neck could have the same rolling mechanisms of the limbs which would be easier to think, but the shoulders are definitely a wall.
This is the Artemis II suit, it appears to be rigid/semi-rigid just like the deep dive suits because it seems that rigid structures are easier to keep pressurised.
Not to mention that most of the training for space missions are done underwater anyway, inside the biggest pools of the world.
The movement of the shoulders are quite complex, and I can't find a good enough image to show all the possible movements you can make.
As you can see, the shoulders allow your arms to reach forward, backwards, upwards and even touch the back of the opposite shoulder.
This is the closest I could find, but it seems just too complex, unlike the previous examples.