Female / Male Body Part Science

December 16, 2020 7:32 AM

So I'm sitting up in bed with my back straight up not against the headboard with my feet straight out in front of me and my S/O says that this position of my body is impossible for men to do. Fascinated I ask why and he goes into some scientific boohblahblah

That ends up with me watching a video of the "chair trick" where a man is asked to do two steps back from the nose point on a wall, bend over in front of the wall till the head touches then pick up this lightweight chair to the chest and at that point stand up again. The feat was impossible for men to execute. It had me wondering are there other movement or posture challenges to men vs. Women or vice versa?

posted by The_imp_inimpossible to Science & Nature (21 answers total)

Link please!

I mean, there are male dancers with loads of flexibility so I find this hard to believe. I can believe it in a general way but not an absolute way. Women tend to carry their center of gravity differently and are often more flexible but there’s such a range.
posted by amanda at 7:40 AM on December 16, 2020 [7 favorites]

Here's a video showing the "chair trick" in two different positions.

I have trouble believing it's absolutely divided along gender lines - it obviously is something to do with mechanics/center of gravity. There's articles on the internet quoting "experts" who suggest that men's longer foot length is the reason they struggle in position #2 but that doesn't explain position #1 issues? I don't get it.
posted by MiraK at 7:43 AM on December 16, 2020 [2 favorites]

He's wrong about the first claim; as a guy, I do not find it impossible to sit up straight in bed, away from the headboard, with my feet/legs straight out in front of me.

The chair trick, though has to do with typical weight distribution. More of mens' weight is above the waist, pitching their center of gravity forward when bent over.
posted by jon1270 at 7:48 AM on December 16, 2020 [8 favorites]

Sorry, for the position in bed are you referring to long sitting? It's difficult for many people to sit in this position because they have tight hamstrings, and men seem to be on average less flexible than women, but there's no anatomical reason men can't get into this position.
posted by autolykos at 7:53 AM on December 16, 2020 [9 favorites]

Yeah, cis women are often more flexible than cis men, and are often wider-hipped in a way that gives them a lower center of gravity. There's a correlation because hormones affect your joints and your bone structure, and cis men and women often have different hormone levels.

The correlation gets stronger in American culture because we encourage athletic girls to do things like gymnastics and skating (which build flexibility, and which often bulk up your lower body more than your upper) and encourage athletic boys to do things like play football and lift weights (which build bulk all over your body at the expense of flexibility).

But it's only a correlation. Bendy cis men and top-heavy cis women might be in the minority, but there are still plenty of both.
posted by nebulawindphone at 7:54 AM on December 16, 2020 [17 favorites]

I've just spent five minutes trying to fail the "chair trick". I'm a pretty ordinarily sized cis man (180cm/80kg/shoe size UK 8-9) and I found it completely possible. I'm only in my socks, though, and most of the people in the videos are wearing shoes. Standing about 10cm further away from the wall did make it impossible because I had to go off-balance forward to touch the wall with my head.

For reference, I also did not find it challenging sitting with my legs straight out in front of me and my back straight up and not against a wall. It's not super comfortable, but it's definitely not impossible for all men.
posted by spielzebub at 7:57 AM on December 16, 2020 [2 favorites]

Interestingly, though, I can't do it in position one in the video MiraK posted.
posted by spielzebub at 8:03 AM on December 16, 2020

I think this has to do with flexibility!

I have very tight hamstrings and my hips are very tight. I cannot sit up straight with my legs out in front of me. My lower back curves and I slouch forward to hold the position.

I do a lot of pilates, which often requires this sitting with your feet out position; if you bend your knees it helps. I bet your husband could do it if he bent his knees.
posted by dazedandconfused at 8:03 AM on December 16, 2020 [1 favorite]

Looking for data on the actual difference in center of gravity for men and women, I found a 1922 article. Continuing to look for more recent data, I found a 2010 article, which cited...the same 1922 article. So back to 1922, which says the average male center of gravity is 56.7% of height, and for women is... apparently behind a paywall: $25 to read the full 1922 article.
posted by Mr.Know-it-some at 8:10 AM on December 16, 2020 [5 favorites]

I am a cisman with very flexible hamstrings and I can 100% do the chair trick. (For reference, I can sink into a straddle from standing.)

One of the links puts distance to the wall at two lengths of your feet, so I tried that--no issues. I also tried it at 1.5 lengths and 3 lengths. 1.5 was fine. 3 lengths I had to warm up a bit for the reasons everyone here is pointing out--it's about weight distribution, so to do it you have to send your butt back a bit with the legs straight, which requires opening the hammies--but could get it as well after about 1.5 minutes of stretching.

edit: I just did this again and I'm slightly off--I'm actually only able to touch the wall with my head in any rotation close to 90 degrees at ~2.75 lengths. Otherwise I'm pitched way forward of 90 degrees at my ankles (ie the ankles make noticeably acute angles). Anyway the rest is correct. :-)
posted by migrantology at 8:25 AM on December 16, 2020 [2 favorites]

Having not much else to do because pandemic, here's my results (cis male, 50+, fairly chunky):

Sitting up straight aka long sitting: No problem. I do this 2-4x a week on a yoga mat on hardwood floor. On the bed is much less comfortable & I can't hold it for long because my bed is soft enough that I start to go V-shaped, which puts pressure on my tummy & diaphragm.

Chair Trick $2 - head against the wall - no problem IF I just bend at the waist "normally" and put my head against the wall.

Here's the key, though . . . Standing about 10cm further away from the wall did make it impossible because I had to go off-balance forward to touch the wall with my head. Yeah, this - if you're strictly following the challenge and pacing off 2 foot-lengths from the wall it puts me noticeably further back from the wall where I'm already leaning forward off balance to get my head against the wall. Then I can't do it. So there's maybe something there about leg-to-torso ratio & foot size?

Chair Trick #1 - heels and legs against the wall - Nope. I can't get more than halfway down in the first place while keeping my heels against the wall without starting to topple over. Which is interesting because I can bend over & touch my toes NOT against a wall no problem. So I guess when I'm touching my toes I'm canting my hips back at least a little?

So, yeah, there's maybe something about how muscle mass is distributed & centers of gravity & skeletal structure PLUS some general cultural stuff about fitness & flexibility wherein there might be a very vaguely general trend for one gender to find something easier than the other, but as always be suspicious of sweeping "It is impossible for [gender] to do Thing."
posted by soundguy99 at 8:28 AM on December 16, 2020 [2 favorites]

The chair challenge is all about center of mass. You can only remain standing if your center of mass stays above your base of support (your feet). As you lean forward your center of mass goes forward too, and you will fall if you lean too far forward without being able to shift something (your butt) backwards to counterbalance. Having larger feet is a disadvantage if you're measuring your steps using them, because it puts you further back from the wall, however larger feet are generally an advantage in these types of challenges because your center of mass can travel farther before it's outside the base of support. Position #1 is definitely easier with larger feet.

It's pretty easy to test this out - just move yourself different distances from the wall (for position #2) and you'll find the dividing line between possible/impossible. For position 1, I was able to do this as a teenager in physics class but I have *ahem* a booty now which has shifted things.

The general estimate for center of gravity for all humans is that it's just anterior to your S2 vertebrae, at somewhere in the range of 55 to 57% of your body height, with men's generally being slightly higher because of increased upper body mass. Please don't believe people online who say men's center of gravity is in their shoulders and women's is in their belly buttons - the actual difference is only a couple of cm either way and can vary pretty widely.
posted by autolykos at 8:30 AM on December 16, 2020 [11 favorites]

As a ciswoman with the World's Tightest Hamstrings (tm) I can't do the long sit at all, and couldn't really manage it even when I was doing yoga regularly. So that's a data point!
posted by Lawn Beaver at 8:31 AM on December 16, 2020 [2 favorites]

Sometimes men interpret a woman doing things they personally aren't able to do as an attack on their ego, so they find comfort in a narrative that it is a womanly thing that women can do and men cannot do. If gender can explain it, then they don't have to feel inferior about it.
posted by ewok_academy at 8:58 AM on December 16, 2020 [17 favorites]

There is more variation among the bodies of cis women and among the bodies of cis men* than there is between the body sizes, flexibilities, bone lengths, fat distributions, and muscle strengths of cis men and cis women.

Which is to say, when you plot thousands of cis men and cis women on “how easily can this position or fear be achieved or completed?” On bell curves, the curve of one group will be very very slightly offset from the curve of the other group. Both curves will be normally distributed.

Bodies are weird and we’ll be well served to stop with the biological determinism associated with assertions like “that’s impossible for men to do.”

I cannot believe I just did a “not on men” on the Internet. But here we are.

*This of course excepts Y carried physical defects, as well as physical structures that are generally determined by sex chromosome, but of course that’s where you’re headed for intersex education and potentially as many as __(I forgot but you can Google!) percent of the population may be intersex. We don’t really know because there’s still a ton of stigma around this, AND medical studies devoted to the area have historically been sketchy as fuck.
posted by bilabial at 9:13 AM on December 16, 2020 [7 favorites]

Yeah, isn’t this just seated dandasana? Men can for sure do this.
posted by en forme de poire at 9:19 AM on December 16, 2020 [3 favorites]

Nthing: some men can do the chair trick (I could in the past, haven't checked in years), many men can sit like that (I still can easily)

I think you're mostly talking about how gender biases and norms shape behavior and those behaviors shape our bodies, and not much at all about science of sex-based differences. E.g. sure, men are often stronger than women, but for just about any man you can find a stronger woman.

In-group variation almost totally swamps any meaningful strict differences between the sexes, and I hope you use this thread to school your husband on his (probably accidental, learned from society since a young age) ultimately sexist thinking.
posted by SaltySalticid at 9:22 AM on December 16, 2020

There do seem to be consistent sex differences in hamstring flexibility and i suspect that has a lot to do with this. Hard to say whether that's cultural or biological or (i suspect) both.
posted by dis_integration at 10:55 AM on December 16, 2020

I'm an almost-50-year old guy, and I can do the chair trick. I can also sit like that.
posted by fimbulvetr at 2:26 PM on December 16, 2020 [1 favorite]

As I have access behind an academic paywall, I was able to take a look at the 1922 paper linked by Mr. Know-it-some. The study looked at a pretty narrow subset of society with a relatively small number of subjects, so shouldn't necessarily be taken as representative of the full range of human body type variation. That said, they report that as a percentage of the person's total height, the center of mass in men is located at 56.18%, with a standard deviation of 0.234%, and in women at 55.44%, with a standard deviation of 1.09%. Underlining the point that bilabial made, this means there's much more variation within each sex than between the average of the sexes. So in their sample, specifically, the 12% of women with the highest centers of mass had higher centers of mass than the 66% of men with the lowest centers of mass. To their credit the authors of the 1922 study make this point fairly clear.

It is often the case that careful scientific measurements can reveal systematic differences between various aspects of biology and behavior in (cisgendered) men and women aside from the basic primary sex characteristics. It is also almost always the case that these systematic differences are smaller than the natural within-group variability. Just as it's fairly obvious that average height of men is greater than the average height of women, but if you were to assume that every man is taller than every woman you'd be wrong an awful lot of the time, one should usually approach claims about supposedly-scientific evidence that some trait is generally true of men but not women, or vice versa, with a hefty dose of skepticism.
posted by biogeo at 4:53 PM on December 16, 2020 [7 favorites]

I'm a cis woman and sitting that way would be uncomfortable for me because of tight hamstrings. I could do it, but not comfortably, not for long. Yes, this is about flexibility, not women and men. Now, it may also be gendered in that men tend to sit with legs asprawl, but that's also a chicken and egg situation.
posted by bluedaisy at 5:50 PM on December 16, 2020