I'm working on some biologically realistic interpretations of fantasy creatures, such as Orcs and Ogres. They're signature superhuman strength has been given a scientifically realistic reasoning to it: Their muscle twitch fibres are more fast-twitch than that of a human, whose muscles have mor slow-twitch

For context, muscle-twitch fibres are categorized into two types: The high-power fast-twitch and the high-endurance slow-twitch. Many species, including most primates, feature more fast-twitch muscles than slow-twitch muscles. They have a higher power output but lower endurance compared to humans, whose muscles are around an entire 50% comprised of slow-twitch muscles (give or take 10% or so).

The biggest benefit of having slow-twitch muscle fibres is a lower energy cost, which in turn can have excess energy stored as either fat or used to fuel the brain (At least, this is my understanding)

However, could a humanoid species with more fast-twitch muscle fibres (like say, comparable to that of a chimpanzee or a gorilla) still maintain something close enough to human-level intelligence? Fast-twitch muscle fibres, due to being higher power, take up more energy, hence their lower endurance. This would leave less room for fat reserves, and more importantly brain fuel.

Is there any special setup that could be used so that a humanoid creature can have both fast-twitch muscle fibres AND human level intellect? I already can imagine compromises such as a higher caloric intake, less endurance, and less capacity to build fat, but would this all truly work? What else would need to change in order for a humanoid species to have intellect comparable to a human?

(When I say "comparable", I mean in terms of comprehension, versatility, vocabulary, adaptability, intellectual capacity, and strategizing. I imagine the traits of their brains might need to be changed too.)

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    $\begingroup$ you don't have ot change the muscle fiber just changing muscle recruitment will be enough, it is the reason a chimps is stronger than a human but has poorer motor control. $\endgroup$
    – John
    Jun 3, 2020 at 16:42
  • $\begingroup$ Ever heard of the Kzinti? $\endgroup$ Jun 3, 2020 at 16:58
  • $\begingroup$ Does anyone know if overheating and brain damage are major risks with this setup? There would have to be some point this would be a limit. ncbi.nlm.nih.gov/pmc/articles/PMC4944502 Probably no big problem until quite intense levels, though. $\endgroup$
    – DWKraus
    Jun 4, 2020 at 4:07

2 Answers 2


There's no contradiction

It's true that 'fast-twitch' muscles are more powerful than 'slow twitch'. However, what isn't true is that the primary advantage is based off of slow twitch taking more power - it actually doesn't! Since slow twitch muscles are endurance muscles, in the short term, fast twitch will eclipse them, however, long term the slow twitch endurance muscles will burn more energy. Humans are creatures designed for endurance, not power.

Additionally, it doesn't matter how strong the muscles are or how much energy they take in. There's not a hard limit to how much energy a human, or any creature, can take in and use - as long as they have the systems and facilities to it, they can use it. Saying creatures spend more energy on muscles and therefore can't be as smart is like saying professional athletes can't be intelligent because they have too many muscles.

  • $\begingroup$ While there is no theoretical limit on how much energy a living creature can use, there's a practical one. The amount of energy an hervibore can get depends on how much plants can find and eat (and digesting plants is quite an energy and time demanding process). For a carnivore, it all depends on how much it can hunt. There's always competency out there, so evolution pressures energy needs of all species down to a minimum, as your high-energy consuming humanoid would be the first to die of hunger. $\endgroup$
    – Rekesoft
    Jun 5, 2020 at 10:38

The brain is plastic, it adapts... When an athlete gains muscle mass some stem cells on the back of the head are used to create new brain cells, and when animals become bigger with more muscle their brains grow too.

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    $\begingroup$ The number of neurons don't increase over time. At most it decreases. $\endgroup$
    – L.Dutch
    Jun 3, 2020 at 18:50
  • $\begingroup$ @L.Dutch-ReinstateMonica do not know where you heard that but the brain does indeed increase the number of neurons over time, it is a generally accepted and well studied mechanism of human anatomy $\endgroup$
    – user76358
    Jun 10, 2020 at 18:54

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