Body Composition
Objectives
• Define body composition and explain its
relationship to body weight.
• Calculate your BMI and classify yourself as
underweight, normal, overweight, or obese.
• Know what a healthy range is for body-fat
percentage, as well as the health
consequences of having too much or too
little body fat.
(continued)
Objectives (continued)
• Explain the various methods of body
composition assessment and identify each
as a laboratory-based or field technique.
• Calculate your ideal body weight using
information from your body composition
assessment.
• Describe recommended strategies for
losing and gaining weight.
Quantity Versus Quality
• A scale provides the quantity but tells
nothing about the quality of the body
weight.
• Although two people can have exactly the
same height and weight, the quality of their
bodies can be very different.
• Body composition focuses on quality.
Body Composition Defined
• Body composition refers to the
components of the human body and their
proportions.
• It reflects the relative amounts of fat and
fat-free mass in the body.
• It is one of the health-related components
of fitness.
Fat and Fat-Free Components
• Fat-free mass includes everything other than fat.
• Fat mass can be grouped into two categories:
– Essential fat—crucial for normal body functioning
• Men: estimated to be 3%
• Women: estimated to be 12%
– Nonessential fat—storage fat for energy, protection, and
insulation
• Percent body fat: Total body fat is usually
expressed relative to body weight.
Measuring Body Composition
• Height–weight charts
• BMI
– Body weight (kg) / height squared (m2)
– Not the same as body-fat percentage
– Predictor of early mortality
• Waist circumference
– Measurement at narrowest part of torso
– Android obesity
– Gynoid obesity
Risk of Premature Death Increases
as BMI Increases
Health Consequences of Overweight
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Cardiovascular and coronary heart disease
Hypertension
High cholesterol
Diabetes and blood sugar problems
Certain types of cancers
Arthritis
Menstrual irregularities
Health Consequences of Underweight
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Malnourishment
Fluid and electrolyte imbalances
Weak bones and osteoporosis
Muscle wasting
Kidney disorders
Reproductive disorders
Sudden death
Lab Methods
of Body Composition Assessment
• Hydrodensitometry
• Air-displacement plethysmography
(Bod Pod)
• Dual-energy X-ray absorptiometry (DXA)
Field Methods
of Body Composition Assessment
• Skinfold method
• Bioelectrical impedance analysis (BIA)
• Near-infrared interactance (NIR)
Hydrodensitometry
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Also known as underwater weighing.
Based on Archimedes’ principle.
Muscle sinks and fat floats.
Measures body volume.
Subsequent measurements:
– Body density = body mass / body volume.
– % body fat = (4.95 / body density) – 4.50.
• A measure of residual lung volume is
needed for greatest accuracy.
Air-Displacement Plethysmography
• The Bod Pod is used to get this measure.
• Body volume is measured by air
displacement instead of water
displacement.
• This method is quicker and easier than
hydrodensitometry.
• To get an accurate result, the subject must
wear tight-fitting clothing.
The Bod Pod
Dual-Energy X-Ray Absorptiometry
(DXA)
• This method uses a low-radiation X-ray to
identify underlying tissue.
• It measures bone mineral content and bone
density as well as fat and lean tissue.
• It is capable of taking regional assessments
(e.g., trunk versus periphery).
• It is easy for the participant.
• It is costly and requires an X-ray technician.
DXA Method: Full-Body Scan
Skinfold Method
• Measures folded skin and the fat trapped in
the fold.
• Assumes a relationship between
subcutaneous fat and total body fat.
• The technician needs to be skilled:
– Proper site location
– Pinching technique
– Equation selection
• Not recommended for obese participants.
Skinfold Measures Fat
and Layers of Skin
Bioelectrical Impedance Analysis
(BIA)
• A low-level electrical current is passed
through the body, and the flow of current is
measured.
• Water and electrolytes are primarily in the
fat-free tissue (good conductor).
• Resistance comes from fat (poor
conductor).
• Measures total body water, fat-free mass,
and body fat.
(continued)
Bioelectrical Impedance Analysis
(BIA) (continued)
• BIA is more comfortable than skinfold
measurements for the participant and
requires less skill from the technician.
• It requires adhering to pretesting hydration
guidelines.
• This method is recommended over
skinfolds for obese people.
• Inexpensive home-use analyzers are
available.
Near-Infrared Interactance (NIR)
• NIR uses an infrared light and reads the
amount of light reflected to determine the
composition of underlying tissue.
• NIR is rapid and painless for the participant
and is easy for the technician to administer.
• Accuracy is questionable.
Determining Ideal Body Weight
• To find your current body-fat percentage,
have your body composition measured by a
trained technician.
• Set a reasonable goal. Men should have 5%
to 25% body fat; women, 15% to 35%.
• To determine your target body weight,
divide your fat-free mass by the percent of
fat-free mass that you would like to have.
Reducing Body Fat
• A body fat reduction plan should allow you
to retain or gain muscle.
• Weight loss should be gradual: 1 or 2 lb (.5
or 1 kg) per week.
Gaining Weight
• The goal should be to gain muscle mass
rather than fat mass. This is achieved by
lifting weights.
• Eat ample calories, about 400 to 500 more
calories per day than your body needs.