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Usually, on Earth the 4 most popular ways to move are:

  1. get dragged by the waves or winds

  2. grow towards the place you want to reach

  3. pump liquids onto tubes making them move

  4. contract fibers one onto the other to pull limbs

There's also some other crazy ways to get from point A to point B but they are more situational.

I want a creature which moves by having muscles that instead of pulling fibers together, they push each other out. Basically an elastic band that works the other way around.

So how would muscles that push work?

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    $\begingroup$ Would this method really be all that different from #3, muscular hydrostats? $\endgroup$
    – rek
    Jan 12, 2021 at 17:31
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    $\begingroup$ Insect uses flow of blood to extend their legs just saying ;D $\endgroup$
    – user6760
    Jan 12, 2021 at 17:42
  • $\begingroup$ @user6760 yeah thats number 3 $\endgroup$
    – user81643
    Jan 12, 2021 at 17:50
  • $\begingroup$ @rek well i asked for a reverse muscle not a hydraulic $\endgroup$
    – user81643
    Jan 12, 2021 at 17:52
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    $\begingroup$ @TheSquare-CubeLaw yeah muscles can relax and stretch, but a lot of powerlifters rip off muscles from their bones and have tendons snapping like crazy when doing movements that require a strong stretch. Something working with water pressure would be even weaker and dependant on the material, you'd need muscles of literal titanium to make it worth the trouble. $\endgroup$
    – user81643
    Jan 12, 2021 at 18:59

4 Answers 4

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IT'S A BIT OF A STRETCH:

Here are my thoughts on the topic in order of probability. I think the closest to what you're looking for is the second. Hydraulics are a good choice, but it's already been covered well in other answers.

  • If there were some sort of molecular, cellular, or tissue spring, which was contracted by muscle and held in place, but then could be released, it could use the stored energy of the spring for extending the structure. The spring would be doing the extension, not the muscle. Tendons can store energy this way, but the underlying muscle still powers by contraction. These springs in nature allow concentrated power to be applied to sudden tasks (the classical example being a velociraptor claw, although the exact mechanisms and uses of these claws is under debate)
  • I think it would be theoretically possible for an extender mechanism, but the nature of organic material is such that an extender-muscle would need to somehow be rigid. Think of it this way - you can contract a thread by pulling on it, but not normally pushing. I envision interlocking molecular tubes, so the contraction of the muscular molecules causes the ends of the tubes to slide outward, even while the distance between the contracting part shortens. Imagine a syringe where the plunger was surrounded with muscle, where as the muscle contracted, it pushed the plunger outward out of the syringe. Mechanically it would do what you wanted without having to reinvent the muscle. I think carbon nanotubes would be excellent structural components for such a structure. These tubes can push against tissue or other tubes, causing a extending motion as bundles of these structures extend together. It would also be possible for the muscle to contract from outside a tubule structure and exert force via a thread/wire-like structure like a tiny clockwork machine moved by wires.
  • Another possible mechanism might involve a functionally threaded structure. Spirals exist in nature, and could meld together like gears (creating a functional motion similar to that of the tubes I was mentioning before) but the mechanics would need to look something more like that of a robot for something like this to work, and I can't quite envision all the moving parts.
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Turgor pressure.

This is essentially hydraulics. Plants use this for movements including rapid ones. Mimosa is the sentitive plant which will fold up if you touch it.

Mechanical and electrical anisotropy in Mimosa pudica pulvini

Thigmonastic or seismonastic movements in Mimosa pudica, such as the response to touch, appear to be regulated by electrical, hydrodynamical and chemical signal transduction... As the petiole falls, the volume of the lower part of the pulvinus decreases and the volume of the upper part increases due to the redistribution of water between the upper and lower parts of the pulvinus. This hydroelastic process is reversible. During the relaxation of the petiole, the volume of the lower part of the pulvinus increases and the volume of the upper part decreases. Redistribution of ions between the upper and lower parts of a pulvinus causes fast transport of water through aquaporins and causes a fast change in the volume of the motor cells...

Hydraulics work fine for moving plants. I think an issue is containing pressures involved, which is why hydraulics are great for machines that can use strong materials. Decrease in turgor pressure can also be used to pull.

Humans also have organs which function by redistribution of blood and changes in turgor pressure.

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The tongue

Easiest experiment in the world. Stick your tongue out. To feel how much pressure is available, hold a finger lightly in front of the tip of your tongue and push with the tongue. Also it is not trivially easy to push the tongue back into your mouth with a single finger - try it!

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  • $\begingroup$ OK, but the "push" comes from the muscles on the sides of the tongue contracting in towards the center. Since OP is asking for a mechanism, that needs to be explained. $\endgroup$
    – Spencer
    Jan 12, 2021 at 23:59
  • $\begingroup$ @Spencer - Interesting. Do you have a link to a source that details this mechanism? I couldn't find one so I was relying on empirical evidence. $\endgroup$ Jan 13, 2021 at 0:04
  • $\begingroup$ It was just my variation on the experiment. $\endgroup$
    – Spencer
    Jan 13, 2021 at 0:06
  • $\begingroup$ @Spencer - Your point about needing to explain the mechanism is a good one. It seems that further research is required. It's late here so maybe I'll continue tomorrow. $\endgroup$ Jan 13, 2021 at 0:08
  • $\begingroup$ @chasly-supportsMonica It's called a muscular hydrostat. Octopus arms are the same. Although, IMO it makes more sense for bending than pushing. $\endgroup$
    – Will Chen
    Jan 13, 2021 at 1:51
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Have a ring of normal pull-muscles contract around a long bladder filled with fluid.

As the bladder gets thinner, it must also extend longer in order to maintain the same volume.

Pneumatic artificial muscles kinda do this, but in reverse.

(The reasons for creating this hydraulic push-muscle instead of just using the pull-muscles directly would then have to be evolutionary and environmental.)

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