What sort of problems might occur if every human gained extra muscle mass?

Question

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?

Answer 1

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.

Answer 2

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.

@ckersch

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)

Answer 3

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.