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Answer:
Your bodyfat
percentage and Body Mass Index are actually
two very different numbers that can
have very little to do with each other
depending on several factors.
Your body
fat percentage (regardless of the source
you get it from, be it the handheld
bio-impedence electrical machine or
through skinfold calipers) is a measure
of how much fat you have on your body
compared to lean mass in form of muscle,
bone, organs, etc. For example, if you
weigh 200 pounds at 10% bodyfat, you
are carrying 20 pounds of fat on you.
Your Body
Mass Index is a measure of weight compared
to height. It actually has nothing to
do with fat or muscle or anything like
that!
Using
our same example, a person who weighed
200 pounds at 10% bodyfat could be categorized
as obese unless they were at least 6
foot 4!
Body Mass
Index is a simple, quick gauge of your
body based on the combined average data
of the measurements of millions of people.
It does not necessarily apply to an
individual. Your bodyfat percentage
is a far more useful number.
I would
expect these two numbers to agree only
if the person being tested were completely
average, which is hard to expect in
the real world.
As an
aside, the bio-impedence method of testing
bodyfat may be convenient but it is
not all that accurate. The readings
can vary greatly during the course of
a day and can be affected by how much
water you have in you as well as what
you've eaten during the day.
For best
results, use it at the same time every
day (preferable first thing in the morning
before doing anything else). This will
give you a standardized way to compare
your results.
Personally,
those standing bodyfat scales are pretty
much a waste of money. I actually have
one (Tanita Ironman scale that's supposedly
tuned for athletes) and it pegs me at
anywhere between 20% to 36% bodyfat
even though I'm about 8 to 10% or so.
What IS
interesting to think of is that the
scales you stand on are really only
measure bodyfat in your LOWER body.
The current goes from one foot to the
other the quickest route possible. They
may have formulas to estimate upper
body fat and get a total but this fact
makes it very innaccurate for total
body testing. For best results, you
need to go from right or left hand to
opposing foot to get a cross-section
of the whole body.
As for
hyrdation, the better hydrated you are,
the lower your bodyfat levels will record.
Water is a good conductor and more of
it means the current goes through easier
(and muscle has more water than fat).
Also, if you're hydrated, you'll weigh
more than if you are dehydrated, which
will result in lower readings.
Same goes
for eating salami (or any sodium-rich
processed foods). The sodium conducts
the current well and gives lower readings.
These
bf scales are good as a curiosity but
I wouldn't put any stock in them in
terms of giving legitimate numbers,
to be honest.
The one
I have cost me $120 and is a supposedly
good quality BF scale and it still doesn't
work well for me. If you get a cheap
one, you'll really be guessing. You're
better off with a regular scale and
tape measure to throw around your waist
in terms of feedback on fat loss.
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