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Measuring Body
Composition
Whenever we embark on any type of fitness program, we
expect to make some kind of progress. Otherwise, we would
just be wasting our time. Measuring our progress is very
important not only to let us know if and how quickly we are
improving, but also because it provides encouragement for us to
stay on track. However, no measurement is perfectly
accurate, and not all measurements are appropriate for every
goal. Using a measurement that is irrelevant to your
goal is likely to provide meaningless or inaccurate
information. As a result, we should make sure that the
measurements that we take are appropriate for our
goals. The tools and measurements for monitoring
progress can span the full range of indicators that measure
health, physical appearance/body composition, and athletic
performance. However, we will stick to indicators of
physical appearance and body composition because these are the
ones that generate the most interest in health and fitness.
This article will list some measurement parameters along
with their objectivities, accuracies, and with synopses of
their uses and limitations. For the purposes of this
discussion, the objectivity of a measurement is defined as the
reading's independence from individual interpretation.
For example, weight is considered to be very objective because if
the scale shows your weight to be 145 lbs, it will do so
regardless of what you want it to show. Also, for the
purposes of this discussion, the accuracy is defined as the
ability to accurately indicate body composition such as fat
percentage.
Weight
Theory: Heavier person is fatter.
Objectivity/Accuracy: Very objective but very
inaccurate
When used by itself, weight gives no useful information on body
composition. However, when combined with percentage
body fat measurements, it can be useful in estimating lean
mass. It can also be useful for athletes who compete in
weight divisions (i.e. boxers).
Body Mass Index or BMI (Weight in kg divided by
height2 in meters)
Theory: If 2 people are the same weight, then the
shorter is fatter.
Objectivity/Accuracy: Very Objective but
very inaccurate
BMI gives no useful information on body composition and it
is useless for computing lean mass. However, its
convenience makes it useful for studies of a general
population.
Girth Measurements with a Measuring Tape
Theory: Smaller girth (especially around
waist) is leaner.
Objectivity/Accuracy: Reasonably objective
but slightly inaccurate
Girth measurements do not directly measure body composition but
they can tell you if your waist or hip measurement is expanding
or shrinking. Girth measurements are very convenient
and are useful for monitoring trends. In addition, using a
measuring tape is the best way to see if you will fit into those
new clothes.
Photograph
Theory: If you look leaner, then you
probably are.
Objectivity/Accuracy: Somewhat
objective but somewhat inaccurate
The results that you get from a photograph are affected by
the lighting, the camera and even photographer
technique. However, if you use constant photography
conditions, before and after pictures are very useful for
measuring your progress.
Buoyancy Measurement in a Flotion Tank
Theory: Muscle is less buoyant than
fat.
Objectivity/Accuracy: Very objective and
very accurate
Buoyancy measurement is the most accurate way to measure body
composition on living subjects and is widely accepted as the gold
standard. However, it is inconvenient and it requires
a high degree of technical competence from the tester.
Also, trapped gas can affect the measurement. Regardless,
it is the most accurate way to measure percentage body fat for
purposes of estimating lean mass.
Skin Fold Measurements with Calipers
Theory: The less you can pinch, the leaner
you are.
Objectivity/Accuracy: Reasonably objective
and reasonably accurate
Skin fold measurements are second to buoyancy measurements in
accuracy. However, it only measures subcutaneous (below the
skin) fat and it requires some technical knowledge by the person
who is taking the measurement. Generally, its accuracy
increases with the number of places on your body that are
measured. It can be very useful because fat below the skin
is usually what determines how well your abs are showing or how
you look in a swimsuit.
Bioelectrical Impedance
Theory: Muscle conducts electricity better
than fat does.
Objectivity/Accuracy: Very objective but
slightly accurate
This measurement assumes average arm length for height, along
with constant hydration and electrolyte levels. Deviations
in any one of these parameters can significantly affect the
measurement. However, it is convenient and easy to use.
As mentioned before, we pursue fitness for a variety
of reasons and there are a variety of methods for
measuring our progress towards our goals. Whether your goal
is to fit into those new clothes, to look great for that photo
shoot, or simply to feel better, it is important that the means
of measuring your progress is relevant to your individual
goal.
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