I don't just mean testosterone. I mean, are men's muscles just structurally different due to testosterone?

No. Men just have more muscle tissue. They also have denser bones. But the differences are in quantity, not quality.

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Evolutionary Design: Men are built to hunt and protect, while woman play the major role in reproduction and care taking of the next generation. This diversification happens during puberty and needs to be seen in context. It does not mean women can't be stronger than man, but at the extremes its quite clear , see top level sports.

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The structure of muscles are the same but you have more amounts of it on men, although ofc testosterone is super potent on muscle buildup so unless women get huge amounts of this, they can't build as much muscle as a man. Testosterone is produced in a small amounts in women but not that much.

TLDR: Built different.

great but common missunderstanding of evolution. men "are" not "designed" by or with the purpose for anything (that would be creationism). over the years stronger men survived and gave their genes to the next generation, same with women that where light and able to flee. those advantages survived the next generations and so on. when more and more society evolved, beauty ideals and preached roles where having an impact on evolution as well.

Men tend to have larger muscles, heart and lungs than women of the same height giving them more physical power. Men's bones will be denser and longer giving them better leverages. Men's circulatory system will be more robust with thicker veins and arteries giving them better energy delivery.

To grossly simplify, this is caused by exposure to testosterone during development, with men receiving much more testosterone than women.

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Certainly breeding choices come into play here. There is nothing preventing a female from having denser bones, bigger muscles, and a nice moustache. Testosterone does its thing. On the flip side of that coin if a Male has excess Estrogen they will lose muscle mass, bone density, start to develop breasts, grow wider hips and be prone to melancholy where as testostorone drives "rage" (unless countered by serotonin).

Also, I could be wrong about this. Women who go through menopause generally have "rage" do to the steady testosterone levels with depleting estrogen.

The primary drivers of the dimorphism between men and women are sex steroid hormones during puberty.
This is a really good review of the topic https://doi.org/10.1016/j.beem.2007.04.007
Just the abstract is sufficient to give a good overview.

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Exactly, evolution doesn't design anything. Natural selection just results in certain traits that lead to survival of the species. In a different environment, humans may have evolved differently.

So substitute the words "evolved for" for "designed for" and the statement stands.

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Women gain just as much muscle mass from strength training as men, relative to what they started with. But because they usually start from a much lower baseline, their overall strength will still be lower than that of a comparably trained man.

>Men are built to hunt and protect

Intrasexual competition is a more common culprit in explaining sexual dimorphism. Dimorphism correlates strongly with mating system across mammals, such that higher size dimorphism corresponds with more polygyny and male-male competition.

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No, no, no. Unless you're talking about women with testicles. Testosterone is a game-changer, and while teenage boys will grow muscles from looking at a weighted barbell, women take years to grow unless they inject some maleness.

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They have massively higher concentrations of androgen receptors independent of testosterone exposure. Amongst elite athletes men tend to have a higher 1rm off of say, an 8 rep max.

IE a man and a woman of equal muscle mass and leverages can both squat 315x8. The man will have a 1rm fairly higher then the female even though rep max was the same.

Men are better at maximal efforts, likely from muscle fiber composition favoring 1rm and the androgen receptors.

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Men tend to have much higher neuromuscular efficiency than women. The ability to activate more muscle fibers during contraction. This is mostly due to testosterone exposure during gestation.

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How does competition create sexual dimorphism?

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That article is about “body composition in relation to lean, fat and bone masses”, not necessarily the phenotypic differences between the sexes. Meaning, how muscle, fat, and bone are distributed on the body differentially between the sexes and over time. You can’t pretend like a 6’5” 300lb dude is only that big because of hormones. Genetics has a lot to do with it.

Where one sex (usually males) competes physically for the other sex, there is selection pressure for large size, musculature, weaponry like antlers and horns, territoriality, and aggression. The winners of these contests reap huge rewards in terms of mating (Bateman's principle), which is why sexual dimorphism is associated with polygyny. In monogamous species, there is much less incentive to invest energy into intrasexual competition.

Thanks for the reply. Also I've been looking for an answer to my question and haven't found anything on it. Do you happen to know what would create the attraction for sexual dimorphic features such as fat deposition in females? I understand that they survived better in the past but how does actual attraction come into play?

The best available info I could find is here:

https://embryo.asu.edu/pages/sex-determination-humans

https://guides.hostos.cuny.edu/bio140/13-44

https://academic.oup.com/edrv/article/41/3/bnaa003/5770947

TLDR: Every fertilized egg would develop into a female without chemical prompting. If a fertilized egg has a “Sex Determining Region Y,” gene it is likely to be male by creating the “SRY” protein. However the SRY proteins do not have all the information necessary to create a male. Some people with the SRY gene are not fully male.

A embryo with the SRY gene will likely create testes, which produce comparatively much greater androgens during puberty than embryos without testes. This results in:

>Marked changes occur in body composition during puberty that lead to boys becoming stronger and more anabolic compared with female counterparts. Androgens alone increase both whole body and muscle protein synthesis, though this is increased further in the presence of GH (236). Similarly, GH works synergistically with testosterone during puberty to reduce adiposity and increase lean muscle mass (236). Muscular strength accelerates rapidly after 13 or 14 years of age in response to rising testosterone and GH . . .

Testosterone also directly increases bone density and increases the effects of Insulin Like Growth Factor-1. All this results in greater muscle and bone growth than if the androgens were not present in the same quantities.

TLDR was TL so the Short, Short answer is:

Testes produce more androgens than Ovaries, especially during puberty, which results in significantly greater muscle and bone anabolic activity.

> men tend to have a higher 1rm off of say, an 8 rep max.

What do these letters mean? Rm? Rep?

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1 repetition maximum. A rep being one of a movement type.

Like benching 225 12 times would be 12 reps at 225, for a set of 12.

1 rm or rep max would be the most weight you can lift a single time.

Men who have the same 12 repetition maximum (the most weight they can lift 12 times in a row) as women, will have a higher 1 rep maximum then women. Women seem to have better endurance relative to their maximal strength, while men have better power relative to their lifting endurance.

Female Olympic athletes are just much better at handling total training volume relative to 1rm then men are.

IE attempting 5 reps at 95 percent of 1rm could be possible for women. For men it's likely they would fail after 2 reps and begin to risk serious injury.

The tldr is that women are more resistant to fatigue then men while lifting heavy, but men are capable of producing more power with equal muscle mass. Part of it is cns, part hormones. Women who take steroids still can't equal 1rm of steroid free men when muscle mass is the same.

> Evolutionary Design: Men are built to hunt and protect, while woman play the major role in reproduction and care taking of the next generation.

I don't think this stands up to scrutiny. Firstly the idea that hunting was a male activity in forager societies has been called into question by archeological evidence such as https://www.science.org/doi/10.1126/sciadv.abd0310

Secondly, the same sexual dimorphism exists in the other Hominidae (great apes) to a varying extent, with no correlation to how much hunting the species does. In particular gorillas do virtually no hunting but have males much larger than females. An evolutionary explanation for sexual dimorphism that's applicable to all great apes is simpler than appealing to a different explanation for each species.

I agree with other answers that fighting is a more probable driver of sexual dimorphism in great apes than hunting. If, in human forager societies, more hunting was done by men this could be as much the result as the cause of the sexual dimorphism.

I don't know about the microscale. There is variation in muscle tissue, such as "fast twitch" vs "slow twitch" fibres, but I don't know of any studies correlating (or not) such variation with sex.

Men on average have more muscle mass and lower body fat percentage. As well as that there is a difference in muscle distribution. Compared to women, men have a significant advantage in upper body strength but a more modest advantage in lower body strength. I've seen varying figures from different sources but the difference clearly exists. Upper body strength is important for punching, throwing objects, and wielding weapons - all abilities required to fight and to hunt.

Even if they're the same height and weight and have the same skill and general fitness, that upper body strength gives the man an advantage in a fight, which is likely to be one reason why combat sports usually separate men and women in competition even though they also have weight classes.

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Size is not a sexual dimorphism in the human species, male and female are relatively similar in size, there are actually many women taller than man. Size, which is linked to strength, makes/made a man go up in the competence hierarchy, which makes him more attractive as a mating partner, which in turn means that the genes responsible are passed on to the next generation.

Humans do show size dimorphism (about 15%), albeit not as much as some other primates, and certainly not as much as elephant seals. There is also substantial dimorphism in upper body musculature relative to lower body, suggesting adaptations for fighting.

The rest of what you described is Darwin's male-male competition and female choice.

Thats a size difference in my eyes, due to a complex mating behavior humans developed over time and male physical aspects is one parameter that played/plays quite a significant role, which also indicates health.. likely the major aspects in mate selection on both sides. And could you please define what you refer to when using the term size dimorphism.

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You might want to look in Fisherian runaway selection and Zahavian honest signalling. Both are explanations for the evolution of preferences for sexually selected traits, but would take a while to write out here. Wikipedia is good.

Such traits don't need to offer a survival advantage to evolve. In fact, many examples probably offer a survival disadvantage.

Size dimorphism means a difference in size between the two sexes of a species.

Even the fibers themselves are different. You can tell male from female just from the composition.

That makes no sense. Anyone who has ever lifted weights can tell you the gains come easily when starting out and taper off.

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What are the testosterone levels and estrogen levels in cis men and women? I'm curious because I found out fairly recently that both have both hormones, but in different rates.

Yeah, men and women need both estrogen and testosterone for good health.

Etrogen: Men 40 pg/ml, Women 350 pg/ml (depending on stage of menstrual cycle)

Testoserone: Men 300 ng/dl, Women 15–70 ng/dl

Thank you. Interesting to hear. The female testosterone levels vary too? Or is that on an individual basis, ie. it's constant, but one woman might have more testosteron than the other?

And follow-up: HRT basically just shifts the balance, right?

Yes. Every hormone in everyone varies. Natural hormone levels change over time (minutes, hours, days, months, years). The relative amounts do sit in particular ranges, and those ranges vary between men and women.

HRT I don't know much about, but I assume so. I believe one issue is that it lacks the variations of natural hormone secretion. But that's way out of my wheelhouse.

Interesting point because humans are not particularly sexually dimorphic when compared to other animals, and even other primates. Sexual selection is often overlooked in evolution, but females play a large role in what traits are conserved and which are lost. For humans, parental involvement was favored over size/strength of males. This is why we pair-bond and are mostly monogamous with fewer offspring.