maximum weight on a Bianchi Eros frame.

David Damerell wrote:
Quoting 41 :
About BMI vs cubic law: a mouse, rat, pig, or super-morbidly obese
person is starting to approximate a cube or an oblate spheroid

But the square-cube law has nothing to do with the actual shape of the
body in question.

If you only knew geometry, you might think that. But then, you would be
wrong. See reply to CC below.ê

Chalo wrote:
41 wrote:

Once you stop getting taller, you start getting shorter, regardless of
age.

If so, the effect should be fairly imperceptible until the geriatric
phase. Although height for anybody can vary about an inch over the
course of a single day, a consistent one inch loss from let's say age
20 to 40 would be unusual.

It's more pronounced for me than for many other folks probably
be cause I broke my back in two places as a teenager, but no doubt also
due to my unusual height and weight.

Sorry about the back. If the broken back were treated by spinal fusion
and who knows what else, I would expect the effect to be less
pronounced. This because most of the variation in height seems to be
water loss from the disks during the course of upright posture, and
re-absorption when lying prone, i.e. according to the diurnal cycle.
Your unusual height does mean that a smaller proportional loss can lead
to a larger absolute loss. I do believe it is the extra 100+ pounds
compressing you. If you tried inversion boots you might get it back,
and then some...


About BMI vs cubic law: a mouse, rat, pig, or super-morbidly obese
person is starting to approximate a cube or an oblate spheroid
http://tinyurl.com/bhskg
but a lean person is not.

It doesn't matter what the shape is, volume is still directly
proportional to the cube of the length.

Not in all circumstances. In particular, not in the ones that apply
here. Consider this example:

Cube dimensions lxwxh = 1x1x1 = volume of 1.
Now double length to 2: volume 2x1x1 = volume of 2
double length to 4: volume 4x1x1 = volume of 4.

So, this does not follow the cubic power law, nor for that matter the
BMI. But wait you say, the three versions of the cube are not
proportionally scaled. That is exactly the point: a normal person of
height 6'8" does NOT have the same proportions as one of 4'8".
(However, a really fat small mouse, pig or person, and a really fat
large mouse, pig or person, are closer to proportionally sized,
according to my eagle eyeball, because the limbs sort of disappear
under all the blubber.) This is likely why the BMI works better than
the cube law.


Both cube laws and the BMI are just
approximations, neither of which is perfect.

Not perfect, sure, but consider this: If two bodies are exactly
identical in every respect except overall scale, then BMI considers one
of them to have a "better" weight than the other. Obviously this is
fallacious.

I wouldn't say so, because if you scale up a small person to the size
of large person, you get a deformed freak, well, more or less. Extreme
example going the other way: scale down an adult to the size of a baby.
That looks freakish and bizarre, as da Vinci notably observed, and as
you can see in many pre- da Vinci paintings.

We see this in bicycling when we note that taller people can have the
handlebars proportionally lower than shorter people.

This is also one of the reasons I find the complaints about Barbie's
proportionally humungous knockers and tiny waist to be fallacious. A
small doll should not necessarily be in the same proportions as a
regular size person in order to look right. Consider Raggedy Anne.


BMI is pretty good, an d people are interested in it not because of any
geometrical rationalization, but because it is easy to calculate from
available data and seems well correlated with % body fat and health and
lifespan.

The more you look at it, the more it looks like plain old hokum.

^^^^^
I believe the term you are searching for is (statistical) index or
indicator. That means the easily calculated value suggests, with some
statistical spread, some other value that is not so easily calculated.
The latter in this case would be % body fat, or even better, mortality
and morbidity. In any case, for the individual, BMI, like any other
index, or even any sophisticated measurement of body fat, or even
simply weighing on a scale, is entirely unnecessary except for
psychological stimulation: if you've got flab, you are overweight. You
don't need anything fancy to tell you that, a mirror, your fingers, or
your jeans will tell you. For normal health, that's all anyone needs to
know. The epidemiologists and so on can't go around sticking their
fingers in everybody's waistband or asking them to strip, but they have
height and weight statistics up to their eyeballs, so BMI or something
similar is just what they need. For their purposes, it works reasonably
well..

Quoting Chalo :
Qui si parla Campagnolo wrote:
Many as heavy and strong as you
or more so, have used square taper for decades w/o any failures.
And several people who post here in this group have broken them. It's
not rare and it's the result of just plain bad engineering.

http://www.chiark.greenend.org.uk/~a...mp/bbshear.jpg

Friend of mine - about 6'2", some fat but not much. Not exactly Chalo's
build.
--
David Damerell Kill the tomato!
Today is First Aponoia, July.

Quoting Peter Cole :
David Damerell:
Indeed, it is obvious that BMI is bogus for people of unusual height
precisely because it does not take account of the square-cube law.
We've been over this before. BMI works for me (6'10"/230lb), so does the
max HR formula. As unusual as I am statistically, I'm only 17% or so
taller than the average male of European descent,

That produces an error of 17% in the predicted "correct" weight, then.

that for my ancestral gene pool (Dutch). As far as I know, I'm to scale,
in that all my parts, including eyes (opthalmologist says) and teeth/jaw
(dentist says) are just that much bigger.

Then it ought to be immediately apparent that if BMI were to be correct,
it would have to include the cube of height as a term, not the square.

scaled up a bit. For my average build, the BMI seems to scale well,
perhaps not perfectly, as my body fat is low-ish and the BMI has me at
the high end of normal/recommended.

That sounds like the expected 17% error, yes.
--
David Damerell Kill the tomato!
Today is First Aponoia, July.

Quoting 41 :
David Damerell wrote:
Quoting 41 :
About BMI vs cubic law: a mouse, rat, pig, or super-morbidly obese
person is starting to approximate a cube or an oblate spheroid
But the square-cube law has nothing to do with the actual shape of the
body in question.
If you only knew geometry, you might think that. But then, you would be
wrong.

Not really, no. You've observed that some specific proportions like head
size have to change, but the gross proportions like the barrel of the
chest all scale up. For BMI to be correct, the other two linear dimensions
would have to increase as the root of height - tall people would be
impossibly skinny, and short ones like hack-fantasy dwarves.

Or one could just notice that very tall people all report that BMI makes
them overweight unless they are stupidly thin (notice that Peter Cole
actually reports an error when claiming there isn't one) and very short
people can eat pies all day and still not have BMI claim they are
overweight.
--
David Damerell Kill the tomato!
Today is First Aponoia, July.

David Damerell wrote:

For BMI to be correct

No one is saying that the BMI is "correct". In fact, there is always
extra research going on to "correct" it further, e.g. by introducing a
body build factor or whatever.

The point is that a simple cube law isn't either. These issues are well
known, the geometry contribution of scaling in relation to body size is
discussed all the time, if it were just a simple geometrical problem,
there would not have been all this research over all these years into
allometry, going back many years, e.g.

http://tinyurl.com/a5fty
http://tinyurl.com/ak7vo

Why would the field (allometry or allometric relationships) need to
contain more than 1 sentence if the cube law were "correct"?

Qui si parla Campagnolo wrote:

And as I have mentioned, there is something amiss in the ones you used
and I do not think it's a design flaw. Many as heavy and strong as you
or more so, have used square taper for decades w/o any failures.


Peter,

Have you seen more broken Shimano Square BBs than Campy BBs? The only
Campy I have seen are the really old ones in the picture collection
referred to frequently by this newsgroup.

-n

"David Damerell" wrote in message
...
Quoting Llatikcuf :
If you refer to the simple geometric principle that volume is
proportional to height^3, then you'll see that 6'8" and 300 lbs is
equivalent to 6'0" and 219 lbs., or 5'6" and 168 lbs. That's normal
for fit men of heavy build at those heights.
that's not how I remember health class-
[BMI]

Indeed, it is obvious that BMI is bogus for people of unusual height
precisely because it does not take account of the square-cube law.
--

Moreover, BMI is flawed because it does not differentiate between lean body
mass and bodyfat. A chronic alcoholic who's skinny with a pot belly may have
a "healthy" BMI, while a bodybuilder may be considered obese. It's a
measuring stick for the couch potato, but that's about it.

Mike
5'7" 175"---BMI 27.4---overweight. Overweight, my ass! It's taken lots of
squats and benches to get this overweight. :-)

Quoting 41 :
David Damerell wrote:
For BMI to be correct
No one is saying that the BMI is "correct".

Well, yes, people are. Every time someone of unusual height goes to their
GP and is told something based on BMI, that's saying that BMI is correct.

The point is that a simple cube law isn't either.

Indeed - but it's a damn sight closer.
--
David Damerell Distortion Field!
Today is Gaiman, July - a public holiday.

David Damerell wrote:
Quoting 41 :

The point is that a simple cube law isn't either.

Indeed - but it's a damn sight closer.

This is a very active research field and I'm sure the professional
community would love to hear this exciting news. I wonder why they all
missed it?

E=ma^2 x
E=mb^2 x
E=mc^2 AHA!

I guess you are saying that Quetelet, and those who resurrected BMI,
only did two tries to get to kg^2 and they stopped. If only they had
gone one further!

Quetelet was one of or the founder of modern social and medical
statistics and he was no fool. A cubic relation may work better FOR YOU
and for some others he this is what statistical spread is all about.
But the BMI is preferred over it on the basis of a much larger sample,
where extremes are relatively rare. Again, there are "corrected"
versions of it based on body type and other factors. And again, what is
the point of BMI or any other relation for an individual, who can see
right away whether he has flab or not, and moreover what is the
validity of ANY such index for an individual, when such indexes must
have statistical scatter? BMI or something else only makes sense for
professionals doing populational studies. But strangely the cubic is
not yet finding favor as a replacement.

Previously you wrote:
You've observed that some specific proportions like head size have to change, but the gross
proportions like the barrel of the chest all scale up.

No, this is wrong. For example, my chest is shaped nothing at all like
any usable barrel. Second, more to the point, the proportions of limb
length to trunk length change, often markedly. If you have ever floated
in a pool you may have noticed that these have different densities.