I'm doing some background work for a scifi/horror piece, and it includes "orcs", who are just humans that have undergone a series of mutations - the main one being that they no longer produce myostatin. This results in them having more muscle mass than a normal human - according to that article, in cattle this can result in up to 40% more than average. There have also been a few humans born with similar mutations, so it strikes me as being plausible.

One problem that the Wikipedia article above mentions is that it may result in the "orcs" requiring more food than a normal human - which, if nothing else, gives them a plausible reason to feud with normal humans. Another problem, again from that article, is that long-distance endurance and muscle mass aren't necessarily linked. What other problems might occur as a result of this, particularly for a character who recently mutated instead of inheriting the mutation?

  • $\begingroup$ The other problem also mentioned is that the muscle tissues do not develop is a normal way like it does by exercising. Meaning that they have a weird shape and a questionable usefulness. $\endgroup$
    – Vincent
    Feb 13, 2015 at 17:22
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    $\begingroup$ My yoga pants would stretch even more causing another recall due to exposed undies. $\endgroup$
    – DA.
    Feb 13, 2015 at 18:15
  • $\begingroup$ Also, I see your article already mentioned it, but for those interested, the Belgian Blue is a really interesting breed of cattle that has 'double muscles'. en.wikipedia.org/wiki/Belgian_Blue $\endgroup$
    – DA.
    Feb 13, 2015 at 18:17
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    $\begingroup$ The average power lifter surely has 40% more muscle mass than I do, and requires more food. This hasn't lead to them "feuding" with me, though, thank goodness ;-) Face it, if orcs and humans feud it'll be because people are racist scumbags. $\endgroup$ Feb 17, 2015 at 8:50
  • $\begingroup$ @SteveJessop Many are of the opinion that racism stems from subconscious economic/material concerns. $\endgroup$ Sep 7, 2016 at 19:15

3 Answers 3


Some problems associated with an increase in muscle mass could include increased food requirements, birthing difficulties, heart problems, faster aging, and skeletal deformities. Individuals with this increased muscle mass may also suffer more from environmental effects in cold climates.

Heart disease

Increasing the size of muscles will probably also increase the size of muscles in the heart. While improving blood flow to the muscles, this can also lead to complications. Hypertrophic cardiomyopathy is a condition in which the walls of the heart are thickened due to genetic factors, and can lead to sudden unexpected death due to heart failure in some cases.

Increased food needs

As you mentioned, more muscles need more calories, which generally means more food. Simple enough.

Birthing difficulties

The sorts of mutations that lead to increased muscle mass also often lead to increased birth weights. This can cause complications during birthing, which are seen in some animals with muscular hyperplasia like the Belgian Blue, a type of cow.

Faster aging

Aging has been shown to correlate inversely with caloric intake, which will be increased by the presence of more muscle. Muscular stem cells may also be depleted faster in individuals with less myostatin, a potential complication which is being investigated as a potential complication of treating MS through myostatin inhibition.

Skeletal deformities

While not all animals with increased muscle mass due to absence of inhibition of myostatin experience this, in whippets, the presence of a homozygous mutation in a gene can lead to shorter limbs and a pronounced overbite.

Adverse weather issues

Lastly, genes that cause heavy muscling also lead to less body fat. While advantageous for models, body fat can also be crucial to helping people thrive in cold conditions by providing an extra layer of insulation below the skin. Without this layer of fat, people will get cold faster, exposing them to frost bite as well as requiring more food to produce heat to stay warm. Your orcs will do best when sticking to low, food-rich regions.

  • $\begingroup$ Those are very useful links, particularly that PubMed article. Thanks! $\endgroup$ Feb 13, 2015 at 20:21
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    $\begingroup$ I find it interesting that many of these consequence (short lives, skeletal deformaties, etc) are common features of orcish descriptions. $\endgroup$
    – Tim B
    Feb 13, 2015 at 20:29
  • $\begingroup$ It appears that study actually shows that there is not a correlation between RMR and aging. Read the conclusion - "Our data challenge the theory that RMR is a significant determinant of oxidative stress and therefore contributes to the aging process." $\endgroup$
    – Samuel
    Feb 16, 2015 at 2:31
  • $\begingroup$ Good catch. I replaced that source with one looking at (and actually finding, this time!) a correlation between caloric intake and aging. $\endgroup$
    – ckersch
    Feb 16, 2015 at 3:25
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    $\begingroup$ "Has been shown" is probably over-stating the case if you had to cherry-pick studies to do it. "Is sufficiently plausible for fiction", sure, easily :-) $\endgroup$ Feb 17, 2015 at 8:55

The thing with postnatal inhibition of myostatin is that you will not be able to achieve 40% increase in muscle mass no matter what you do.

You see, when there is a genetic loss of myostatin, the number of muscle fibre as well as muscle fibre diameter both increase (hypertrophy and hyperplasia), which gets you about 40%. However, after birth, of you manage to get rid of myostatin, you only increase the muscle fibre diameter(only hypertrophy) which is somewhere in the region of about 16-20% depending on which technique you use.

If you are looking at before birth alterations, might I suggest also looking into combined myostatin inhibition and follistatin upregulation ? Scientific literature has shown that muscle mass may increase by about 4 times.

Alternatively, if you are taking of a postnatal augmentation so to speak, I'd suggest messing about with the growth hormone, (though be warned that will screw up a lot of things, mostly making the individual more aggressive (as orcs are meant to be).

Also note that myostatin affects the fast muscle fibre more than the slow types. You use fast types for quick burst activities and the slow types for well.. endurance. So myostatin inhibition may actually be detrimental for endurance training (also causes a fibre type shift, converting some slow fibres to fast fibres).

Do note that when you increase muscle mass like this, you are not necessarily increasing quality. You will be increasing the total force output sure, but the muscle on the whole becomes weaker (specific force decreases) and there are cases of brittle tendons and other things.


You make a few good points but

I must note here that Myostatin inhibiton has been shown to have no increase in the size of the heart (as its a different fibre type).

Muscle stem cells are not affected in any way by myostatin inhibition (acts by a completely different pathway)

  • $\begingroup$ Quite interesting points, there. I had considered growth hormone earlier - again, it's plausible, but has downsides. So, it looks like my orcs are going to have some serious health problems. $\endgroup$ Feb 17, 2015 at 8:45
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    $\begingroup$ @PhilipRowlands: I think the general theme is that if you change a human in any way you're liable to create some serious health problems, because there are so many delicate inter-dependent systems available for you to mess up. On the other hand, serious health problems means serious selection pressure in favour of any existing variation or further mutation that mitigates the problems. So give 'em a few generations to evolve and they'll be right as rain (or extinct) ;-) $\endgroup$ Feb 17, 2015 at 9:00
  • $\begingroup$ @SteveJessop hadn't realised that, but then I'm not a biologist or a doctor :) That said, my main storyline is set a few generations after the orcs start appearing, so perhaps they'll be in better health than their great-grandparents. $\endgroup$ Feb 17, 2015 at 9:08
  • $\begingroup$ I said "a few", but really that was for emphasis. 3 generations isn't enough for the mitigating genes to propagate throughout the population, unless it's as simple as "X% of the original orcs were basically unviable: they or their descendants have dropped dead. The other 100-X% had the orc-survival gene, that was nearly-neutral in normal humans, and handwaves away the worst of the health problems". You'd probably have to consult a qualified speculative geneticist to get an idea how many generations it "should" take to mitigate particular problems ;-) $\endgroup$ Feb 17, 2015 at 9:38

The more muscle, the more calories needed. However, that doesn't necessarily mean more food needed. Just higher calories.

But yes, food could be one problem.

We may also see issues with the physical world having to become upgraded. Plane seats. Car interiors. Mattresses. Granted, we have to accommodate some of that today in some regions (namely the US) due to higher fat mass. So in terms of size issues, there may be a parallel there.

And then things such as ladders. Instead of being rated for 200lbs, maybe they'd have to be rated for 300lbs. So there could be a need to increase natural resources to accommodate this more massive human.

  • $\begingroup$ That is a very good point too. I hadn't considered how ladders etc. would be affected by this. Thanks! $\endgroup$ Feb 13, 2015 at 20:30

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