Body Composition
Laboratory Assignment
Procedural Instructions
1. Do not eat large quantities within 12 hours of the lab.
2. Do not drink large quantities of alcohol or beverages containing caffeine within 12 hours of the lab.
3. Make sure you are normally hydrated by drinking regularly in the 12 hours before the lab.
4. Bring a towel and bathing suit for the underwater weighing.
Computational Instructions
When computing body composition variables, round to the following significant decimal places:
%fat, fat weight, fat-free weight, ideal fat weight, body weight, ideal body weight, BMI, W/H ratio
– 1 decimal place
skinfolds – 1 decimal place
residual volume – 3 decimal places in liters; no decimal place in milliliters
density – 5 decimal places
Lab Protocol
1. Determine your height and weight.
2. Body Mass Index. Compute your body mass index ( p.40 in text) on your spreadsheet and classify
your BMI using Table 1 below.
3. Waist to Hip Ratio. Measure your hip and waist circumferences as per the instructions in your text
p. 41. Compute your WHR on your spreadsheet and evaluate it using Table 2 below.
4. Skinfolds. Refer to pages 62-72 for general instructions. Each person in each group should
measure the skinfolds of every other person in the group and record on the data sheet. One
person should measure all 7 skinfolds in succession and then the next person measures all 7 and then
the next. Mark each skinfold site with a marking pen. After all persons in the group have measured
every other person in the group, average the values for each site. If any measurement made at any
site is more than 10% different from the average, everyone should remeasure that site and continue
to do so until everyone is within 5 mm of the average (you compute a new average each time a remeasurement is made. Measure each of the seven skinfolds identified in the Jackson et al. 7 skinfold
equation (Box 4-3) and defined in Box 4-2, p. 65. Three of the same skinfolds will be used in the
Jackson et al. 3 skinfold equation listed in the same box. The skinfold sites are specifically
described in Box 4-2. The sites are also shown in Fig. 4-7, p. 66. Compute density using your
spreadsheet. Convert density into %fat on your spreadsheet using the Siri equation: %fat =
(495/density)- 450. Compute, on your spreadsheet the FM, FFM, and the IBW. Classify your %
body fat as determined by each method using Table 1 below. The standard error of estimate for
these equations is 4% units of body fat.
5. Bioelectric Impedance. Determine your body composition using two methods of BIA. The first
method is called whole body BIA as it determines the resistance to current flow between the foot and
the hands (ie. The entire body except for the head). The second method is called segmental BIA
because it determines the resistance to current flow between one foot, through the hips and the other
foot (ie. Just the lower extremeties).
Whole Body BIA. First, using the RJL BIA system, determine the whole body resistance value.
Next, compute FFM on your spreadsheet using the resistance value from whole body bioelectric
impedance as per the class demonstration and information on p.56 in your text. Follow the
guidelines listed regarding preparation for being measured using bioelectric impedance. Use the
appropriate equation provided in Table 3 below. Note that these equations compute FFM in
kilograms, not pounds and height is in cm and weight is in kilograms. After computing FFM,
compute FM, %fat, density, IBW on your spreadsheet. Convert all weights to pounds. Classify
your %fat computed in this manner using Table 1. The standard error of etimate for this method
is 4% units of body fat.
Segmental BIA. Using the Tanita BIA system, record the value for %fat following the instructions
posted next to the instrument. Enter this value into your spreadsheet in the appropriate column and
then compute the values for density, FM, FFM and IBW. The standard error of estimate for this
method is 5% units of body fat.
6. Underwater Weighing. Determine density on your spreadsheet using underwater-weighing and
compute %fat using the same equation you used for #4 above (Siri equation). Once you have %fat,
compute FM, FFM, IBW on your spreadsheet. Refer to p. 59-61 in the text for methodology [Note.
Density values could conceivably range from 0.9 (corresponds to 100% fat) to 1.1 (corresponds
to 0% fat)]. Values outside this range are incorrect. Make sure you are getting a reasonable
density value. Carry your density value to 5 decimal places. Classify your % fat using Table 2
below. The standard error of estimate for this method is 2.5 % units of body fat.
7. Air Displacement Plethysmography (Bod Pod). This will be performed on the first body
composition lab day. Prior to this assessment you must determine your total lung capacity. To do
this you must first determine your vital capacity as per the instruction below in Estimating Residual
Volume. Once you have determined vital capacity you must then compute residual volume and then
sum the vital capacity and residual volume to get your total lung capacity (see the data sheet). When
you have your total lung capacity you then can do the Bod Pod assessment. In order to do the body
pod you must wear tight fitting shorts or swimsuit. You will also need to wear a swim cap but that
will be provided. (Note: You can use your vital capacity determined for the Bod Pod when you
do the Under Water Weighing).
Estimating Residual Volume. In order to determine density by underwater weighing, you must
know your residual volume and for the BOD POD you must know your total lung capacity. You will
estimate your residual volume by taking a percentage of your vital capacity. First, measure your
vital capacity using the spirometer. The vital capacity volume read off the spirometer’s graph paper
must be corrected for the temperature of the spirometer using the BTPS correction factors listed
below. Multiply the vital capacity volume from the spirometer (the uncorrected value) times the
BTPS correction factor to get the actual volume of the vital capacity in your lungs (corrected vital
capacity). Once this conversion has been made, residual volume is estimated by multiplying your
corrected vital capacity by 0.28 if you are female, and by 0.24 if you are male. The total lung
capacity is the sum of the vital capacity and the residual volume.
You also need to know the density of the water in the weighing tank in order to compute density.
The density of the water is dependent on the temperature of the water. Use the appropriate density
value (in the following table) based on the temperature of the water.
Temperature of
Spirometer °C
BTPS Correction
Factor
18
19
20
21
22
23
24
25
26
27
28
1.114
1.108
1.102
1.096
1.091
1.085
1.080
1.075
1.068
1.063
1.057
H2O Temp
°C
30
31
32
33
34
35
36
37
H2O Density
0.9957
0.9954
0.9951
0.9947
0.9944
0.9941
0.9937
0.9934
7. Completely fill in the Body Composition Data Sheet including the Summary Table. Use the values
for density and %fat from calculations from your spreadsheet. In order to fill in the summary
table, you must select a value for your ideal percent fat. You then use this value to compute your
ideal body weights (IBW). For the density from whole body BIA measurement, you must compute
density by working backward from the %fat which you compute from initially knowing FFM. Once
you have %fat from both BIA methods, use the same conversion equation (Siri equation) you have
used for skinfolds and UWW to convert the densities to %fat. You just rearrange the equation to
solve for density since you know %fat.
Excel Spreadsheet. Using Excel, create a spreadsheet which computes all the values for your specific
data identical to what is on the Excel sample sheet. Leave the data for the sample male and female in
the spreadsheet in rows 2 and 3 and put your data and computations in row 4 of the spreadsheet with
your name (last name first) in column A. In order to make sure your have the correct computations on
the spreadsheet, compute each of the calculated variables using the data for the sample male and
female. You should get the same calculated values that are already in the spread sheet. If you do this,
when you compute your data, the answers will be correct. When computing the data for the various
body composition methods you must use an IF Statement if there is a different equation for males
and females.
When you print the spreadsheet to turn in, do the following:
(1) reduce the wasted space between columns as much as possible (squeeze the columns to
where there is no space on either side of the numbers/letters. Do not put any borders
around any of the columns or rows.
(2) grey the background of each column in which you compute density
(2) print in landscape view and print on two pages with page 1 going up to and including the
column for ideal % fat (column V)and page two from the BMI column (column W) to the
end of the spreadsheet. The easiest way to do this is to select the columns you want to print
and then print the selection. You also need to “fit to one page” and it will automatically be
reduced to fit on one page.
(3) print the gridlines that separate each cell. Gridlines are not borders. To print the gridlines
you have to go to “page setup” and then click on the option to print gridlines.
Answer each of the following questions. Put the number of the questions (1, 2, 3, etc) and then the
specific part of the question where appropriate (A, B, C, etc) in front of each response.
1. In order to covert a density into a %fat using the Siri equation three assumptions have to be
made. List those three assumptions? In order to compute density if you know the %fat using
the Siri equation you have to rearrange the equation to solve for density. What is the correct
rearranged equation to solve for density (i. solve the equation for density)
2. Under water weighing can be a very accurate methods but it is very dependent on good subject
cooperation. Explain the specific effect each of the following factors would have on the
density determined from UWW (ie. Would it increase or decrease the density and specifically
why would it have that effect?): A) The subject did not have their head completely under the
water at the time the weight was determined. B) The subject was touching the bottom of the
tank with their feet at the time the weight was determined. C) The subject did not fully expire
all their air at the time the underwater weight was determined. D) The subject did not make a
full expiration at the time the vital capacity was measured but did make a full expiration when
the underwater weight was measured. (hint: you can check it out with your spreadsheet)
3. Bioelectric impedance measures the resistance to current flow (impedance) and then computes
a %fat value based on the impedance. The BIA methods can be significantly affected by the
water content of the body. Explain the specific effect each of the following scenarios would
have on the determination of % fat using BIA and why it has the effect. A) the impedance
measurement is made immediately after a male has completed a 5 mile run in a relatively heat
stressed environment. B) the impedance is measured when a female is in her water-retention
stage of her menstrual cycle. C) the impedance is measured when the subject has a full bladder,
and D) the subject is a male with gynoid fat distribution and the segmental BIA is used.
4. Explain the specific effect of each of the following on the measurement of % fat using the
BOD POD? A) The subject wears loose fitting shorts ( males) or a blousy bathing suit (females)
when the procedure is performed; B) The total lung volume of the subject was underestimated
by 25% and this low value was used in the computation of % fat in the BOD POD.
5. The skinfold method of determining body composition can be affected by numerous factors
related to measuring the skinfold or to the equation used. Explain the specific effect each of the
following scenarios would have on the determination of density using the skinfold method and
why it has the effect. A) in determining the skinfold thickness three measurements are made in
succession at each skinfold site before measuring the next site and the average if the three
measurements is used as the skinfold at each site. B) a skinfold equation developed on females
is mistakenly used for a male subject.
In preparing your responses to the questions above, follow these directions:
1. Type your responses using #12 Times New Roman font, double spaced with 1 inch
margins top, bottom, left and right. Print only on the front of the page.
2. Put your name and class number in the top left hand corner of the first page.
3. This lab will be graded on the items specified on the Lab Evaluation Sheet included in
your packet of printed material.
4. Turn in the assignment with the following pages in this order and stapled in top lefthand corner: (1) Lab Report 3 Evaluation Sheet with your name and class number
filled in, (2) responses to the questions with each response identified with the same
number (1, 2, 3, etc) as the questions above, (3) Excel spreadsheet, (4) Summary table
with all values typed in, and (5) data sheets with all values typed in.
5. Late assignments will be accepted but there is a 5% per day penalty for being late until
the total penalty accrues to 50%. The lab is late when it is not turned in at the
scheduled time in class. After the penalty reaches 50%, there is no further penalty. It
is always better turn in something rather than nothing. It is usually better to take a 1-
or 2- day late penalty and turn in a complete lab than to turn in an incomplete lab on
time.
Table 1. BMI and Percent Fat Standards in Adult Males and Females
Adult Males
AGE
20-39
40-59
60-79
Increased Risk
Healthy
Increased Risk
High Risk
(BMI<18.5)
(BMI 18.524.9)
8-19%
11-21%
13-24%
(BMI 25-29.9)
(BMI 30+)
20-24%
22-27%
25-29%
≥25%
≥28%
≥30%
33-38%
34-39%
36-41%
≥39%
≥40%
≥42%
≤7.9%
≤10.9%
≤12.9%
Adult Females
20-39
40-59
60-79
≤20.9%
≤22.9%
≤23.9%
21-32%
23-33%
24-35%
Source: Data from Nieman, David. Exercise Testing and Prescription: A Health Related Approach,
McGraw-Hill Higher Education, 2003, p. 133.
Table 2. Waist-to-Hip Ratio Risk Standards
Risk Classification
Age
Low
Moderate
High
Very High
20-29
<0.83
0.83-0.88
0.89-0.94
>0.94
Males
30-39
<0.84
0.84-0.91
0.92-0.96
>0.94
40-49
<0.88
0.88-0.95
0.96-1.00
>1.00
50-59
<0.90
0.90-0.96
0.97-1.02
>1.02
60-69
<0.91
0.91-0.98
0.99-1.03
>1.03
20-29
<0.71
0.71-0.77
0.78-0.82
>0.82
Females
30-39
<0.72
0.72-0.78
0.79-0.84
>0.84
40-49
<0.73
0.73-0.79
0.80-0.87
>0.87
50-59
<0.74
0.74-0.81
0.82-0.88
>0.88
60-69
<0.76
0.76-0.83
0.84-0.90
>0.90
Source: Heyward, VH. Applied Body Composition Assessment. Human Kinetics, 1996.
Table 3. Bioelectrical Impedance Analysis Prediction Equations
Gender
Equation
Male
FFM(kg)= (0.0006636 * ht2) – (0.02117 * R) + (0.62854 * Wt) –
(0.1238 * age) + 9.33285
FFM(kg) = (0.000646 * ht2) – (0.014 * R) + (0.421 * Wt) + 10.4
Female
Note:
Ht is in centimeters
Wt is in kilograms
R is resistance from the BIA analyzer (the larger number)
Age is in years