You may know the popular belief that people are taller in the morning than they are in the evening.
A change of height depending on time.
Is it true? There's only one way to know: by doing the experiment!
This one will us to another experiment, then another.... Well, you'll see.
In order to measure myself, I'll be using this board and shelf bracket to make sure my measurements
are perpendicular to the wall.
This isn't ideal, especially considering that I'll be measuring myself alone;
but what we really want is a means of measurement that will give us reliable results.
I'll measure myself twice each day: once in the morning, and once in the evening.
What I want to find out is the difference between the two measures, if there is one.
While I make my measurements, you can start thinking about what the results will be and why.
Results: on the first morning, I am 172,8cm tall. In the evening, I am 171,35cm tall.
That's a difference of 1,45cm. What's it like the next day? Over 2 weeks?
The results are surprisingly constant.
On average, I am 172,9cm tall in the morning and 171cm tall in the evening.
We get a difference of 1,9cm or ~1% of my height.
It isn't just a myth: people are indeed taller in the morning!
After my experiment, I searched the literature and found the same exact results:
1,9cm of difference, 1% of my height.
I thought that the results raised more questions than they gave answers, though.
Do we grow smaller in a constant way throughout the day? Do we get even shorter if we stay up all night?
I measured myself at regular intervals during one day and the results were very surprising.
It only took an hour for me to lose 80% of the height I had gained through the night!
Even worse: after only 40 minutes, I had already lost 60% of the height I had worked so hard to regain.
However, as you can see, there seems to be a limit to the amount of height you can lose after that.
OK, but then, if I take a 1-hour nap, will I be taller again? If I sleep for 2 days, will I keep growing?
That's the hardest thing to measure: how long does it take for me to win back those 1,9cm (and perhaps even more)?
For this experiment, I got myself to get up in the middle of the night for a week
at different intervals of time so that I could measure myself.
On average, we need 2 to 2,5 hours to win back 60% of the lost 1,9cm.
We only needed 40 minutes in the previous test.
After a good 5 hour's sleep, no more increase: all 1,9cm have been recovered.
Therefore, a 1-hour nap wouldn't be enough.
These are all my results over a 24-hour period:
there is a variation of about 2cm, by which my height drops quickly in the morning
and comes back slower during the night.
Now comes the obvious question: why do we shrink when we get up?
There's clearly something up with the position change from laying down to standing up.
You guessed it: gravity.
When laying down, the body is under less of its own pressure. The reason our height varies
is because of certain body parts that allow it to.
What body parts? It could be the arches of the feet, except the results are unchanged if we
run the tests sitting down (1,9cm; 1% of the height).
This means that the height change must come from the upper body.
From head to toe, the human skeleton has a quasi-continuous bone structure.
There are intervertebral disks between each vertebra.
An intervertebral disk is much more flexible than a bone: when the spine is under pressure
(e.g. when standing up), its most flexible parts will be the ones to move.
So when the spine is put under pressure, the intervertebral disks take the hit.
We have 23 of them which make up 30% of the total length of our spine.
They absorb shocks and allow the vertebrae to move without friction.
To make it simpler, imagine the disks are like a sponge: when you press it, the water
it contains is pushed out. When you lift the pressure, the water comes back in.
That's what happens with our intervertebral disks during the day.
The body's weight puts pressure on the spine and the disks lose water (~20% of their volume)
and when we lay down, the pressure is mostly lifted and the water returns into the disks.
If our height changes so much throughout the day, is it really useful to have it on our ID cards?
I think it should be: 'Height: 1,73cm (early in the morning)
otherwise 1,71cm but that's by my own measurement with my wooden board'.
I invite you to reproduce this simple experiment of measuring yourself in the morning and in the evening.
I'd be especially interested to hear from those of you who are smaller or taller than me and want to give it a go.
Share your results in the comments: do you also find a 1% height variance?
I hope you liked this video. I already knew that our height did indeed change during the day,
but I was very surprised by how consistent the results were and how large the variation turned out to be.
You can now share this video, like it, not like it, whatever feels right.
If you are craving for more, you can follow Scilabus on Facebook, Twitter or on the blog.
I'll see you next time.
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