chapter
4
Body Composition
Rationale for measuring body
composition
• To assess the decrease in body fat
weight that occurs in response to a
weight management program.
• To help athletes determine the best
body composition for performance.
• To monitor fat and fat-free weight in
patients with disease.
• To track long-term changes that occur
in body fat and fat-free mass with
aging.
Important Terms
Fat mass
Fat-free mass
Percent body fat
Obesity
Overweight
Body fat distribution, or fat patterning
Android-type obesity
Gynoid-type obesity
Anthropometry
Body Composition = ratio of fat to fat-free mass.
Comparison of 2- and 4compartment models
Reference proportions
for 4-compartment model.
Height and Weight
• Does not differentiate between fat-free and fat-mass.
Weight measurement alone
cannot accurately determine
body fat status
•People vary widely in
somatype (or body
build)
The 1983 Metropolitan Height-Weight Table
has multiple deficiencies and is no longer
recommended. (p. 45 ACSM)
In older epidemiological studies, obese was defined as 20% or
more overweight using the concept of relative weight (now
rarely used because it was replaced by the BMI):
[(body weight/midpoint value of weight range) x 100]
The table below summarizes standards for relative weight.
Measuring Weight and Height
• Body weight should be measured
on a physician’s balance-beam
scale with minimal clothing and
no shoes.
• Height should be measured with a
stadiometer:
– No shoes, heels together, back
straight, heels, buttocks, shoulders,
and head touching the wall, standing
as tall as possible, and looking
straight ahead.
– Have individual inhale deeply and
hold breath.
Frame size can be estimated by
measuring the width of the elbow.
The table below shows how elbow
breadth can be classified as small,
medium, and large frame (according
to the Metropolitan Life Insurance
Company, as used with their 1983
height-weight table). Also see Table
4-1C for Frame size classifications.
Body mass index (BMI) is a commonly used estimate of
obesity (especially in population studies and surveys). The
Quetelet Index is the most popular BMI estimate: kg/m2
The table below shows the relationship between BMI and
percent body fat (r=0.70, SEE 5% body fat).
Body mass index (BMI)
is a commonly used estimate of obesity
(especially in population studies and surveys).
The Quetelet Index is the most popular BMI estimate: kg/m2
The table below summarizes the 1998 NHLBI Obesity Education Initiative guidelines for
classifying BMI, with disease risk estimated when also related to waist circumference.
(Also see CDC growth charts that classify BMI for boys and girls, aged 2-20 (my website: pdf
documents)
http://www.cdc.gov/nccdphp/dnpa/bmi/childrens_BMI/about_childrens_BMI.htm
Two-Compartment Models
Assume that body is divided into fat and
fat-free mass.
Assume a constant density of fat and fatfree tissues among individuals.
Siri (1961) gives a common model:
%BF = 495/Db – 450.
When components of the fat-free mass
differ from the assumed values,
estimation of %BF is compromised.
There are two-compartment models for
various populations.
Both hydrostatic weighing and air
displacement plethysmography use twocompartment models.
Hydrostatic Weighing
Often referred to as a criterion method
Based on Archimedes’ principle
Used to calculate total body density
Db =
BW
(BW – UWW)
D H2O
– RV
Density of Water
Air displacement plethysmography (BOD POD).
(based on the two-compartment body composition
model).
Bioelectrical Impedance
Analysis (BIA)
Electrical current travels more easily
through tissue containing water and
electrolytes.
Fat does not contain much water;
therefore, electrical flow is impeded.
Fat can be estimated by the impedance
encountered when electrical currents
pass through the body.
(continued)
Leg-to-Leg BIA (Tanita
Corporation)
There are a number of
commercially available BIA
devices.
Values are typically within 4% of
those obtained with
hydrostatic weighing.
It is important to choose the
proper equation for
estimating %BF.
It is critical that person being
tested is normally hydrated.
Tetrapolar BIA technique
Skinfold Measurements
Skinfold Measurements
The most widely used body composition estimate is the skinfold
measurement technique. When performed correctly, skinfold
measures provide an fairly good estimate of percent body fat (r>/=0.80
with underwater weighing). As shown below, the goal is to measure a
double fold of skin and subcutaneous tissue (with sides of skinfold
approximately parallel). The thicker the fat layer, the wider the fold.
Accuracy
in Measuring Skinfolds
To make the measurements as accurate as
possible,
accurately locate the skinfold site,
accurately measure the skinfold, and
choose the appropriate equation for
converting skinfold thickness into %BF.
Basic Rules for
Taking Skinfolds
• Take skinfold measurements on the right side of the body
(most skinfold equations were developed from
measurements on the right side).
• Do not take measurements when the subject's skin is
moist (ensure that the skin is dry, and has no lotion). Also
do not take measurements immediately after exercise or
when the person being measured is overheated because
the shift of body fluid to the skin will inflate normal
skinfold size.
• To reduce error during the learning phase, skinfold sites
should be precisely determined, marked, and verified by a
trained instructor. The largest source of error in skinfold
testing is inaccurate site selection.
Skinfold Rules (continued)
• Firmly grasp the skinfold with the thumb and index
finger of the left hand, and pull away.
• Hold the caliper in the right hand, perpendicular to the
skinfold and with the skinfold dial facing up and easily
readable. Place the caliper heads ¼-½ inch away from
the fingers holding the skinfold. Try to visualize where a
true double-fold of skin thickness is, and place the
caliper heads there.
• Read the caliper dial to the nearest 1 millimeter within 4
seconds. During the measurement, ensure that the left
thumb and forefinger maintains the shape of the skinfold.
• Take a minimum of 2 measurements at each site (at least
15 seconds apart). If the 2 values are within 10% of each
other, take the average.
Thigh Skinfold
Vertical fold on anterior
thigh, midway between
inguinal crease and
proximal border of patella.
Suprailiac Skinfold
Jackson-Pollock procedure: a
diagonal fold is taken with the
natural angle of the iliac crest
at the anterior axillary line
immediately superior to the
iliac crest.
Chest Skinfold
Jackson-Pollock procedure: the chest/pectoral skinfold site is one
half the distance between the anterior axillary line and the nipple for
men, and one third of this distance for women.
Triceps Skinfold
Vertical fold on posterior aspect of arm,
midway between lateral projection of
acromion process and inferior margin of
olecranon process.
Abdomen Skinfold Site
Jackson-Pollock procedure uses a vertical fold 2 cm to
the right of the umbilicus.
Subscapular Skinfold
Diagonal fold just below the
inferior angle of scapula.
Midaxillary Skinfold
Jackson-Pollock procedure, a vertical
fold taken on midaxillary line
at level of xiphoid/sternal
junction.
Medial Calf
A vertical skinfold on
the inside of the calf at
the level of maximum
circumference.
Body fat standards for children/youth ages 6-17 years using
the triceps and subscapular skinfolds (sum).
Body fat standards for children/youth ages 6-17 years using the
triceps and medical calf skinfolds (sum).
Jackson and Pollock generalized body composition equations (Box 4-2, p. 65)
See Table 4-6 (ACSM p. 68) for age- and sex-specific equations to convert body
density to percent body fat.
The Brozek (457– 414.2 /body density ) and Siri (495– 450 /body density )
equations estimate percent body fat from body density. Fat
free mass varied among different groups, and Table 4.6 ACSM
p. 68 summarizes recommended equations.
Nomogram for
estimating
percent body fat
from sum of
three skinfolds.
Durnin and Womersley equations for
calculating body density (based on sum
of 4 skinfolds---biceps, triceps,
subscapula, and suprailiac).
Use Table 4.6 for age- and sex-specific
equations to convert body density to percent
body fat.
Biceps skinfold = vertical fold
on anterior upper arm directly
opposite triceps skinfold site.
Body Fat Ranges for Ages 18 and Older
Classification
Male
Female
Unhealthy range (too low)
<5%
<8%
Acceptable range (lower end)
6-15%
9-23%
Acceptable range (higher end)
16-24%
24-31%
Unhealthy range (too high)
>25%
>32%
Average Body Fat Ranges for Elite Athletes
Males
Females
4-15%
12-26%
Emphasize Leanness
4-10%
10-19%
Team/Dual Sport Athletes
7-21%
18-27%
Power Athletes
5-20%
17-30%
Endurance Athletes
Athletes in Sports that
Girth Measurements:
Important Measurements
Waist: Most narrow part of the torso
between the xiphoid process and the
umbilicus
Abdomen: Circumference of the torso at
the level of the umbilicus
Hips: Maximal circumference of the
buttocks above the gluteal fold
Thigh: Largest circumference of the right
thigh below the gluteal fold
The ratio of waist-to-hip
circumference (WHR) has
been used to determine
android vs. gynoid type of
obesity.
The waist circumference
alone is more commonly
used than the WHR.
A waist-to-hip ratio of more than 0.94 for men or 0.82 for
women is considered too high.
A waist circumference greater than 102 cm in men or 88 cm in
women significantly increases the risk of obesity-related disease.
Calculating Target
Body Weight
It is often important to help clients determine
a healthy and reasonable weight. Calculating
target body weight requires knowledge of
current body weight, %BF, and desired %BF.
FFM
Target body weight =
1–
(
)
Desired %BF
100