Outline:
1.Essential & Storage
Fat
2.Techniques to Assess
Body Composition
3.Determining
Recommended Body
Weight
4.Importance of Regular
Body Composition
Assessment
Chapter 4
Body Composition
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Key Terms
• Body composition: The fat and nonfat
components of the human body; important in
assessing recommended body weight
• Percent body fat: Proportional amount of fat in
the body based on the person’s total weight;
includes both essential and storage fat
• Lean body mass: Body weight without
body fat
• Recommended body weight: Body weight at
which there seems to be no harm to human
health (healthy weight)
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Key Terms
• Overweight: An excess amount of weight
against a given standard such as height or
recommended percent body fat
• Obesity: An excessive accumulation of
body fat usually at least 30% above
recommended body weight
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Height/Weight Tables
• An individual might appear to be overweight
according to height/weight tables but not have
too much body fat
• Examples are football players, body builders,
other athletes with large muscles
• Some people may look skinny or underweight
when they actually are overweight because of
their high body fat
• Physical inactivity and a constant negative
caloric balance both cause a loss in lean body
mass
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Essential and Storage Fat
• Total fat in the human body can be
classified into two types
• Essential fat: Minimal amount of body fat
needed for normal physiological functions;
constitutes about 3% of total weight in
men and 12% in women
• Storage fat: Body fat in excess of
essential fat; stored in adipose tissue
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Typical body composition of an adult
man & woman
• Essential fat
constitutes
about 3% of
the total
weight in men
and 12% in
women
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Body Composition
• Storage fat serves 3 basic functions:
– As an insulator to retain body heat
– As an energy substrate for metabolism
– As padding against physical trauma to the
body
• Men tend to store fat around the waist and
women around the hips and thighs
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Techniques to Assess Body
Composition: DEXA
• Research/medical
facility technique
– Dual energy X-ray
absorptiometry
(DEXA)
– Uses very low-dose
beams of X-ray energy
– Measures total body fat,
fat distribution, bone
density
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Hydrostatic Weighing
• Underwater weighing
• Most common technique used for decades
• A person’s “regular” weight is compared
with underwater weight
• Fat is more buoyant than lean tissue
• Almost all other indirect techniques have
been validated against hydrostatic
weighing
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Hydrostatic Weighing
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Air Displacement
• Individual sits inside small chamber (Bod Pod)
• Computerized pressure sensors determine the
amount of air displaced by the person
• Body volume is calculated by subtracting the air
volume with the person inside the chamber from
the volume of the empty chamber (air in the
lungs is taken into consideration)
• Body density and percent body fat are then
calculated from the body volume
• Less cumbersome to administer
• Takes only about 5 minutes
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The Bod Pod, used for assessment of
body composition
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Skinfold Thickness
• Based on the principle that the amount of fat
beneath the skin is proportional to total body
fat
• Reliable measurements of this tissue give a
good indication of percent body fat
• Skinfold test is done with pressure calipers
• Several sites are measured and percent fat is
estimated from the sum of the three sites
using Tables 4.1 (women) and 4.2 or 4.3
(men)
• All measurements should be taken on the
right side of the body
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Anatomical landmarks for skinfold
measurement
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Skinfold Thickness
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Procedure for body fat assessment
using skinfold thickness technique
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Bioelectrical Impedance
• Simpler to administer, but accuracy is questionable
• Sensors are applied to the skin and a weak
electrical current is run through the body to
estimate body fat, lean body mass, and body water
• Based on the principle that fat tissue is a lessefficient conductor of an electrical current
• The easier the conductance, the leaner the
individual
• Body weight scales with special sensors on the
surface may also be used to perform this procedure
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Body Mass Index (BMI)
• Incorporates height and weight to
estimate critical fat values at which
disease risk increases
– BMI = Body Weight (lbs) x 705 ÷ (height in
inches)2
• Example
– Body Weight = 172 lbs Height = 67 inches
– BMI = 172 x 705 ÷ (67)2
– BMI = 27
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Determination of Body Mass Index
(BMI)
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Mortality risk vs. BMI
• BMI is used almost
exclusively to determine
health risks and mortality
rates associated with
excessive body weight
• Data indicates that disease
risk starts to increase when
BMI exceeds 25
• The risk also increases for
individuals who are
underweight (below 18.5)
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Overweight & obesity trends in the
United States, 1960-2000
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Disease Risk According to Body Mass
Index (BMI)
• BMI does not
differentiate fat from
lean body mass or
note where most of
the fat is located
• Athletes with large
amounts of muscle
mass can fall into the
moderate or high-risk
categories
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Determining Recommended Body
Weight
• Some evidence indicates the mortality rate
for underweight people is high
• The body fat of a healthy thin person is
near the high physical fitness standard
• Underweight people have extremely low
body fat, compromising essential fat
• Normal physiological functions can be
impaired if people fall below the essential
fat standards of 3% for men and 12% for
women
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Typical body composition changes for
adults in the United States
• Because of the typical
reduction in physical
activity, each year the
average person gains
1-2 lbs of body fat
and loses a half a
pound of lean tissue
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Effects of a 6-week aerobics exercise
program on body composition
• Loss of lean body
mass can be offset or
eliminated by
combining a sensible
diet with physical
exercise
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