If a guy is 6'3" and weighs over 200 pounds then it's not a big deal, he might not be that muscley.
However if a guy is 5'3" and weighs over 200 pounds, he's probably built like a rhino. (Assuming he's not obese!)
This got me thinking. When comparing two people's weight, would it not be better to "normalise" their bodyweight to a certain height (such as 5'10") before comparing them? I've never seen people do this before.
What I mean to say is, instead of just saying that Jack is 5'1" and 154 lb, and that John is 6'2" and 223 lb, you could specify the weight that they would be if they were 5'10". Then it would be easy to compare them.
I was playing around with calculating this just now. Here's what I was thinking:
The human body is a 3-dimensional shape. 3D shapes have the following three properties:
1) Length
2) Surface Area
3) Volume and Mass
If you take a 3D object and "blow it up" (as in the way you blow up a photograph to make it bigger), then the way these three properties change can be predicted mathematically.
I'm 5'3" tall. If my height was to be multiplied by 2, making me 10'6", then that would result in my surface area being multiplied by 4, and my volume and mass being multiplied by 8. I'll explain:
The 4 comes from 2 squared (i.e. 2 to the power of 2).
The 8 comes from 2 cubed (i.e. 2 to the power of 3).
Right now I'm 5'3" tall and I weigh 133 pounds. I want to figure out how much I would weight if I were taller, say about 5'10". Here's how I'd do it:
First I'll convert my height to inches, so that's 5 x 12 + 3, which is 63 inches.
Next I convert my target height to inches, so that's 5 x 12 + 10, which is 70 inches.
Now I need to figure out the factor that my height will be multiplied by, so I divide 70 by 63 to give me 1.1111111111.
In order to find out how heavy I would be, I first need to take this figure and cube it, giving 1.371742112482853224.
I then multiply this number by my original weight, and it gives me: 182.4 pounds.
So there you have it: If I was 5'10", I'd weigh 182.4 pounds.
If I was 6'0", I'd weigh 201 pounds!
I learned about this stuff in a nature book. The book had a picture of a rhino and it gave an explanation of why a rhino's limbs are so big in relation to its body size (think about it, it has way bigger limbs relative to its body size than most other animals). Basically the explanation was as follows:
As an animal becomes taller, its surface area and mass increase far faster than its height. For instance if you make an animal 3 times taller, it results in it being 27 times heavier (because 3 cubed is 27).
Because a rhino is so heavy, its strength must be increased by increasing the cross-sectional area of its muscles, meaning it gets thicker limbs.
Another good thing it explained is that strength is proportional to the surface area of the cross-section of a muscle. So in the end, it comes together like this:
If an animal is 3 times taller, then it's 9 times stronger, and it's 27 times heavier.
One thing you can take from this, is that taller people will have more difficulty doing exercises which involve their own bodyweight, e.g. chin-up's. So if you see a tall person doing chin-up's well, you know he's strong!
While you've got the image of a rhino in your head, think about a preying mantis. The preying mantis has very long skinny legs in relation to its body size. If the preying mantis were "blown up" to the size of a human being, it wouldn't be able to support its body with those skinny legs, it would have to make like a rhino and develop thicker stronger limbs.
Here's another measurement I can do: At the moment, my one-repetition maximum for flat bench press is 157 pounds. I want to figure out what that would be if I were 5'10". If I were 5'10", then the cross-sectional area of my muscles would be greater, meaning I'd be stronger. The factor by which the cross-sectional area of my muscles increases is equal to the square of the factor by which my height increases.
We already calculated that if I was 5'10", I'd be 1.111111111111 times as tall. So I just square this number and multiply it by bench max:
157 x (1.1111111111 squared) = 193 pounds
So if I was 5'10", my flat bench 1-rep max would be 193 pounds.
Anyway maybe some will find this stuff interesting. At least I do
Reply With Quote
Originally Posted by Almond
