Body
Composition
Body Composition
2 component model
Fat tissue
Fat free tissue
Body Composition
Why the interest?
Excess body fat
• Hypertension
• Type 2 diabetes
• Hyperlipidemia
• Certain cancers
• Poor performance/function
• Poor self-image
Incident of overweight is ↑ng
Want to “look good”
Body Composition
Terminology
Depot or storage fat – fat stored in
adipose cells as nutritional reserve
Essential fats – fats necessary for
normal physiologic function
Body Composition
Terminology
Lean body mass (wt) – body mass
minus depot fat
Fat free mass (wt) – body mass minus
all fat (depot & essential)
Body Composition
Relative %age of body weight that is
fat & fat-free tissue
Lab & field tests vary in complexity,
expense
Anthropometry
Measurement of
the human body
Anthropometry
Ht/wt
Circumference/girths
Skinfolds
Hydrostatic weighing
Bioelectrical impedance
DXA
TOBEC
X-ray
Body Composition - %Fat
Norms
Classification
Women
Men
Essential Fat
11.0 - 14.0
3.0 - 5.0
Athletes
12.0 – 22.0
5.0 – 13.0
Fitness
16.0 - 25.0
12.0 – 18.0
Potential Risk
26.0 – 31.0
19.0 – 24.0
≥ 32.0
≥ 25.0
Obese
Body Composition - Tests
• Densitometry
– Two component model
• Fat & fat free mass
– Ratio of body mass to body volume
(DB=BW/BV)
– Body mass determined form body weight
– Body volume from under water weighing or
plethysmography
Densitometry
• Hydrostatic (under water)
weighing
–Criterion, gold standard
Densitometry
• Hydrostatic (under water) weighing
– Archimedes’ principle – when a body is
immersed in water, it is buoyed by a
counterforce equal to the weight of the water
displaced
– The loss of weight in water, corrected for
density of the water, allows calculation of
body volume
Densitometry
•
•
•
•
•
RV
Density of H2O
Trapped gas in GI tract (100 ml)
Body weight (dry)
Body weight (wet)
Body Composition Densitometry
Body density =
weight in air
(weight in air – weight in water) – Residual
Density of the water
volume
Body Composition Densitometry
Body density = bone & muscle
more dense than water, fat
tissue less dense
Body Composition Densitometry
Plethysmography
• air displacement – Δs in pressure
in a closed chamber
Bodpod
Body Composition Densitometry
%fat =
457
Body Density
- 414.2
%fat =
495
Body Density
- 450
Body Composition –
Anthropometric Methods
•
•
•
•
Height
Weight
Circumferences
Skinfolds
Body Composition –
Anthropometric Methods
• Reliability & validity
– Skill of the measurer
– Type of caliper or tape measure
– Subject factors related to skinfold
compressibility, edema, & variability in
fat pattern & distribution
– Prediction equation used to estimate
fatness
Body Composition –
Anthropometric Methods
• Body Mass Index (BMI)
–
–
–
–
–
–
Assess weight relative to height
[body weight (kg)/height (m2)]
BMI > 25 – increased health risk
25.0 to 29.9 = Overweight
> 30 = Obese
See Table 4-1 pg.58 & Table 4-2 pg.59
Body Composition –
Anthropometric Methods
• Waist-to-hip circumference
– Body fat distribution
– More fat on trunk (abdominal fat) = greater risk
of HTN, type 2 diabetes, hyperlipidemia, CAD,
premature death
– Health risk is high
•
•
•
•
W/H ratio > 0.94 in young men
W/H ratio > 0.82 in young women
W/H ratio > 1.03 in men 60-69 yrs
W/H ratio > 0.90 in women 60-69 yrs
See Box 4-1 & Table 4-3 pgs.60-61 ACSM GET&P
Classification of Disease Risk Based
on Body mass Index (BMI) and Waist
Circumference (Table4-1)
Disease Risk Relative to normal
Weight and Waist Circumference
BMI, kg/m2
Underweight
<18.5
Men, 102cm;
Women,88cm
…
Normal
18.5-24.9
…
…
Overweight
25.0-29.9
Increased
High
I
30.0-34.9
High
Very high
II
35.0-39.9
Very high
Very high
III
40
Extremely high
Extremely high
Men >102cm;
Women, >88cm
…
Obesity class
Body Composition –
Anthropometric Methods
• Skinfolds
– Amount of subcutaneous fat is
proportional to total body fat
Box 4-2. Standardized Description of
Skinfold Sites & Procedures Continued
• Procedures
– All measurements on the right side of the body
– Caliper should be placed 1 cm away from the thumb
& finger, perpendicular to the skinfold, & halfway
b/n the crest & the base of the fold
Box 4-2. Standardized Description of
Skinfold Sites and Procedures
Continued
– Pinch should be maintained while reading the
caliper
– Wait 1 to 2 s (& not longer) before reading
caliper
– Take duplicate measures at each site & retest if
duplicate measurements are not w/n 1 to 2 mm
– Rotate through measurement sites or allow
time for skin to regain normal texture &
thickness
Box 4-2. Standardized Description of
Skinfold Sites & Procedures
• Skinfold Site
– Abdominal
– Triceps
– Biceps
Vertical fold; 2cm to the right side of
the umbilicus
Vertical fold; on the posterior
midline of the upper arm, halfway
between the acromion & the
olecranon processes, w/ the arm held
freely to the side of the body
Vertical fold; on the anterior aspect of the
arm over the belly of the biceps muscle, 1
cm above the level used to mark the
triceps site
Box 4-2. Standardized Description of
Skinfold Sites & Procedures Continued
• Skinfold Site Continued
– Chest/Pectoral
Diagonal fold; one-half the
distance between the anterior axillary
line & the nipple (men) or one-third
the distance b/n the anterior
axillary line & the nipple (women)
– Medial Calf
Vertical fold; at the maximum
circumference of the calf on the
midline of its medial border
Box 4-2. Standardized Description of
Skinfold Sites & Procedures Continued
• Skinfold Site Continued
– Midaxillary
Vertical fold; on the midaxillary line at
the level of the xiphoid process of the
sternum (An alternate method is a
horizontal fold taken at the level of the
xiphoid/sternal in the midaxillary line
– Subscapular
Diagonal fold (at a 45 angle); 1 to 2
cm below the inferior angle of the
scapula
Box 4-2. Standardized Description of
Skinfold Sites & Procedures Continued
• Suprailiac
Diagonal fold; in line w/
the natural angle of the iliac
crest taken in the anterior
axillary line immediately
superior to the iliac crest
• Thigh
Vertical fold; on the anterior
midline of the thigh, midway
b/ the proximal border
of the patella & the
inguinal crease (hip)
Table 4-5. Body Composition (%Body Fat)
For Men*
Age
Percentile 20-29 30-39 40-49
90
7.1
11.3
13.6
80
9.4
13.9
16.3
70
11.8 15.9
18.1
60
14.1 17.5
19.6
50
15.9 19.0
21.1
40
17.4 20.5
22.5
30
19.5 22.3
24.1
20
22.4 24.2
26.1
10
25.9 27.3
28.9
50-59
15.3
17.9
19.8
21.3
22.7
24.1
25.7
27.5
30.3
60+
15.3
18.4
20.3
22.0
23.5
25.0
26.7
28.5
31.2
Table 4-6. Body Composition (%Body Fat)
For Women*
Age
Percentile 20-29 30-39 40-49
90
14.5 15.5
18.5
80
17.1
18.0
21.3
70
19.0 20.0
23.5
60
20.6 21.6
24.9
50
22.1 23.1
26.4
40
23.7 24.9
28.1
30
25.4 27.0
30.1
20
27.7 29.3
32.1
10
32.1 32.8
35.0
50-59
21.6
25.0
21.3
28.5
30.1
31.6
33.5
35.6
37.9
60+
21.1
25.1
25.0
29.3
30.9
32.5
34.3
36.6
39.3
Body Composition – Other
Techniques
• Bioelectrical Impedance Analysis (BIA)
– Volume of FFM is proportional to the electrical
conductivity of the body
– Small electrical current is passed through body
– Measures resistance to current
• Fat is poor conductor – 14 to 22% water
• Lean tissue is good conductor - >90% water
– Assumes normal hydration
Body Composition – Other
Techniques
• Bioelectrical Impedance Analysis (BIA)
–
–
–
–
Does not require a high degree of technical skill
More comfortable
Requires minimal cooperation
Intrudes less on privacy
Body Composition – Other
Techniques
• Dual Energy X-ray Absorptiometry (DEXA)
– Assess total bone mineral, bone, fat, & lean tissues
– Uses three component model (fat, solids, water)
• Near-infrared interactance (NIR)
– Light absorption & reflection
– Chemical composition of the body
– Accuracy 4 to 11%
Dual X-Ray Absorptiometry
Prediction Equations
• Population specific
– Derived on homogeneous population
• General equations
– Diverse, heterogeneous samples that account
for differences in age, sex, race, ethnicity, etc.
Prediction Equations
• Equation Selection
– To whom is the equation applicable
– Was equation developed on an appropriate reference
model?
– Was a representative sample studied?
– How were predictor variables measured?
– Was the equation cross-validated?
– Does equation give accurate estimates? (2.5 to 3.5% - %fat)
(2.5 to 3.5 kg – FFM)