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Let's say there is a species of intelligent beings who are indistinguishable from humans in every way - except on average they can jump twice as high as the average human, based on Earth gravity.

What physiological differences would be necessary to allow these beings to jump so high, and yet still be able to pass as a normal human? Or, what would the greatest recognizable difference be at first glance?

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  • $\begingroup$ "Indistinguishable from humans in every way" - I assume this doesn't include a detailed medical scan? $\endgroup$ – Dan Smolinske Oct 7 '15 at 17:43
  • $\begingroup$ Do they have to be able to land without injury? $\endgroup$ – Sunspear25 Oct 7 '15 at 18:00
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    $\begingroup$ How high can an average human jump, compared with an Olympic standard high-jumper? Perhaps that's your answer. (Note, height of jump should be defined as distance by which centre of gravity is raised mid-jump above where it was pre-jump. The Fosbury flop technique doesn't alter that distance, it just optimises the position of the rest of the body for clearing a bar, given a guaranteed soft landing). $\endgroup$ – nigel222 Oct 7 '15 at 18:15
  • $\begingroup$ @Dan I originally had "unrecognizable", but it was edited to "indistinguishable". $\endgroup$ – Seth Oct 7 '15 at 20:23
  • $\begingroup$ Never mind the landing, must they be able to jump without injury? One really good spasm of the quadriceps could give admirable height, but it's not something one can do very often. $\endgroup$ – Beta Oct 7 '15 at 22:59
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Well, an easy answer, if you don't want them to look too different, would be that the person's muscle density would be higher. In body building a higher density = more strength rather than a larger mass indicating strength, but I'm not entirely sure how much denser the muscles would need to be. It might just be twice as dense, but I'm not an expert.

You should also take into account the relation of muscle strength to bone strength, which in this article seems to say that bone strength is above average in people that also have strong muscles around that bone. Depending on how high your character jumps, their bones might be strengthened from repeated impact, such as how bones harden in martial arts. Or, just give them thicker bones rather than denser bones.

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Build their muscles from something other than carbon proteins such electroactive polymers. There are several options for alternative muscles besides polymers.

Reducing the weight of the skeleton won't get you much as skeletons don't make up much of the weight of an adult human. Increasing the diameter of muscles doesn't scale very well as the ratio of muscle strength to diameter follows the cube-square law. This limitation can be avoided by making the muscles out of something else with a greater power capacity than normal human muscle.

Evolutionary of Electroactive polymer Muscles

Since movement is such a basic component of life, electroactive polymer (EAP) muscles would need to be realized in a situation where EAP muscles develop before normal protein muscles do. The earth equivalent to when these EAP muscles appear would be around the time of the Cambrian Explosion because if protein muscles show up first, every creature that comes afterwards will have protein muscles as we see here on earth.

The tradeoff between EAP and protein is that protein muscles use predominantly chemical energy in the form of carbs to work (fats work too) while EAPs are purely electrical. Energy storage in terms of batteries or capacitors accessible to the muscle will need to arise and stay charged. I'm sure that Mother Nature could come up with some fabulous dielectric materials for the capacitors.

We know that electricity can be stored and discharged by animals because the electric eel exists. The best way to capture electric eels is to get them to discharge till they're exhausted then wade in and grab them.

So, in addition to being able to jump higher, they'll be able to do about twice what normal humans can do. Run twice as fast, rock climb better.

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  • $\begingroup$ Looking at the Wikipedia article about alternative muscles (you did link to the "Artificial muscle" article), I can't help but ask myself if there is any way any of those could evolve naturally? Maybe the OP wants to allow for artificially designed implants, but I get the feeling that the primary focus of the question is on naturally evolved, biological systems. $\endgroup$ – a CVn Oct 7 '15 at 19:39
  • $\begingroup$ @MichaelKjörling I want to give a flippant "sure they could" but I don't know enough about how electropolymers are made to give an answer. The critical question would be how did they get their evolutionary start? And I'll need to think about that. $\endgroup$ – Green Oct 7 '15 at 19:52
  • $\begingroup$ Mind you, I'm not saying this is necessarily a bad answer. I just think it could be far better if it also gave some -- any, really -- semi-plausible explanation for how any one of these might possibly have evolved naturally. (Once we get into the realm of bio-augmented artificial systems, pretty much anything is theoretically possible, at which point the question would seem to lose much of its value.) $\endgroup$ – a CVn Oct 7 '15 at 20:00
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The thighs and shins are going to give it away. Jump force comes from thighs and if someone can naturally jump twice as high as a normal human, their thighs would be extremely stocky, as compared to humans.

The second give-away (this one would take a keener eye) would be a thicker bone set, specially for the lower part of the body. When landing on the ground after a high jump, the feet have to absorb the shock and then transfer it up to the rest of the body. Being able to jump twice higher than a normal human would also imply those people would be able to handle double the shock which a normal human can. This makes for thicker bones.

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