Body Composition



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.39 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. 39 and in Box. 4.4. Compute your WHR on your spreadsheet and evaluate it using Table 2 at the end of this document.

4. Skinfolds. Refer to pages 61-72 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. There are 5 skinfolds for males (chest, abdomen, thigh, triceps, subscapular) and 4 skinfolds for females (triceps, suprailiac, thigh, abdominal). One person should measure all skinfolds in succession and then the next person measures all 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 5mm different from the average, everyone should re-measure that site and continue to do so until everyone is within 5 mm of the average (you compute a new average each time a re-measurement is made. Measure each of the skinfolds identified in both the Jackson et al. 3 skinfold equations (Box 4-3, p. 68) and defined in Box 4-2, p. 64. The skinfold sites are specifically described in Box 4-2. The sites are also shown in Fig. 4-8, p. 65-67. 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 for each skinfold equation. Classify your % body fat as determined by each method using Table 1 below. The standard error of estimates for these equations are listed in Box 4.3.

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 BTPS Correction H2O Temp H2O Density

Spirometer °C Factor °C

18 1.114 30 0.9957

19 1.108 31 0.9954

20 1.102 32 0.9951

21 1.096 33 0.9947

22 1.091 34 0.9944

23 1.085 35 0.9941

24 1.080 36 0.9937

25 1.075 37 0.9934

26 1.068

27 1.063

28 1.057

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.

Printing the Spreadsheet. 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) Make the background of each of the following Columns a light grey but that you can still see the numbers : Z - Density First 3; AE – Density Second3; AM – Density UWW; AS – Density WB BIA; AY – FFW WB BIA; AZ –Density Seg BIA; BC – Density Bod Pod

(2) print in landscape view and print on two pages with page 1 going up to and including the column for ideal % fat (column U) and page two from the BMI column (column V) 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 regarding the densities of the various components of the body mass and the relationship of the reference body to the measured body. List those three assumptions as 1a, 1b, 1c. ? 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). List this equation as 1d.

2. Under water weighing can be a very accurate method but it is very dependent on good subject cooperation in performing the manuever. Explain the specific effect each of the following scenarios would have on the underwater weight of the subject and the density of the subject determined from UWW (ie. Would it increase or decrease the UWW and density) and specifically why would it have the indicated effect on the UWW and the density.

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 (using the spirometer) but did make a full expiration when the underwater weight was measured. (hint: how is the measured vital capacity eventually used in the computation of density?)

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) a runner runs 5 miles when the temperature is 90 degrees and relative humidity is 70%. At the end of the run the runner weighs 4 lbs less than before the run. The BIA measurement is made right after the runner completes the run..

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.

D) the subject is a male with gynoid fat distribution and the segmental BIA (like we used in lab) is used. (hint: How does the segmental BIA account for the fat mass in the part of the body not measured by the BIA?)

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) or does not wear a swimming cap when the procedure is performed. (hint: How does trapped air affect the measurement?)

B) When determining body composition with the BOD POD, the total lung volume is estimated and plugged into the computation. If the total lung volume of the subject was underestimated by 25% and this low value was used in the determination of %fat in the BOD POD how would it affect the %fat computed? (Hint: How is the lung volume used in the computation?)

5. The skinfold method of determining body composition can be affected by numerous factors related to measuring the skinfold or to the specific 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 (ie. You measure the triceps three times in succession before measuring the next site. before measuring the next site and the average of the three measurements is used as the skinfold value 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 on both sides of the paper.

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 left-hand 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 |Increased Risk |Healthy |Increased Risk |High Risk |

| | | | | |

| |(BMI ................
................

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