SECTION A Background Skinfold Measurements The principle behind the skinfold is that

SECTION A

Background

Skinfold Measurements

The principle behind the skinfold is that the amount of subcutaneous fat is proportional to the total amount of body fat. It is assumed that close to one half or one third of the total body fat is located subcutaneously. The exact proportion of subcutaneous to total body fat varies with sex, age, and ethnicity. Therefore, the regression equations used to convert sum of skinfolds to body density must consider these variables for greater accuracy. Be sure that you are using an equation that was designed for the specific test population (e.g., children, elderly). The accuracy of predicting percent body fat from skinfolds is approximately ±3.5% assuming that appropriate techniques (from a skilled technician) and the correct equations have been used. Also, note that the regression equations for predicting body density and BF% are based on correlations between anthropometric measurements (e.g., skinfolds) and hydrostatic measures of body density. This lab will be using the Jackson and Pollock formulas for the three-site method.

Accuracy of Skinfold Measurements

Reference: Adams, GM & Beam, WC. Exercise Physiology Laboratory Manual, 7th ed. New York, NY: McGraw Hill Education, 2014.

Of the more than 100 equations for the prediction of body density from anthropometric data (with subsequent conversion to percent body fat), the ones from skinfold measurements are considered the most accurate. The relationship between body density and skinfold fat is nonlinear. Therefore, when using a linear equation, accurate predictions would be made for those in the middle values but not at the extremes, where the obese person would be underestimated and the lean person overestimated. The reliability of skinfold measures is high with test-retest reliabilities of 0.94-0.98. In general, the inclusion of three skinfold sites in the regression equation produces a better prediction (lower standard of estimate; SEE) of body density than fewer sites. However, neither the feasibility nor accuracy is improved by using more than three sites. The standard error of the estimate for skinfold prediction of hydrodensitometrically determined body fat is about 3.5% body fat units with the acceptable SEE of 1-1.5% (probably impossible to attain via skinfold measures. The sum of the skinfolds itself may be a more valid indicator of adiposity and better for progressive monitoring of fatness than the prediction of percent fat derived from the skinfolds. Factors that may contribute to measurement error within skinfold assessment include poor anatomical landmark identification, poor measurement technique, an inexperienced evaluator, an extremely obese or extremely lean participant, and an improperly calibrated caliper.

Dual Energy X-Ray Absorptiometry (DEXA)

Reference: Heyward, VH & Gibson, AL. Advanced Fitness Assessment and Exercise Prescription, 7th ed. Champaign, IL: Human Kinetics, 2014.

Dual-energy X-ray absorptiometry (DEXA) is gaining recognition as a reference method for body composition research, especially in clinical settings. This method yields estimates of bone mineral, fat, lean soft tissue, and visceral adipose tissue mass. It is also possible to obtain estimates of these variables at the whole body and the regional (trunk and appendicular) levels. Dual-energy X-ray absorptiometry is an attractive alternative to hydrostatic weighing because it is safe and rapid, it requires minimal client cooperation, and, most importantly, it accounts for individual variability in bone mineral content. The amount of time required per whole-body scan ranges from approximately 8 to 20 min, depending on the model and age of the DEXA machine as well as the stature of the client. The basic principle underlying DEXA technology is that the attenuation of X-rays with high and low photon energies is measurable and dependent on the thickness, density, and chemical composition of the underlying tissue. The attenuation, or weakening, of X-rays through fat, lean tissue, and bone varies due to differences in the densities and chemical compositions of these tissues. The attenuation ratios for the high and low X-ray energies are thought to be constant for all individuals (Pietrobelli et al.

1996).

Accuracy of Dual Energy X-Ray Absorptiometry (DEXA) Measurements

Reference: Heyward, VH & Gibson, AL. Advanced Fitness Assessment and Exercise Prescription, 7th ed. Champaign, IL: Human Kinetics, 2014.

It is difficult to assess the validity of the DEXA method because each of the three manufacturers of DXA instruments has developed its own models and software over the years. As many researchers and some clinicians have discovered, body composition results vary with manufacturer, model, and software version. Thus, some of the variability reported in DEXA validation studies may be due to the different DEXA scanners and software versions. Thus, experts who have reviewed DEXA studies have called for more standardization among manufacturers (Genton et al. 2002; Lohman 1996). Some researchers have reported that the predictive accuracy of DEXA is better than that of hydrostatic weighing (Fields and Goran 2000; Friedl et al. 1992; Prior et al. 1997; Wagner and Heyward 2001; Withers et al. 1998). However, the opposite finding (that hydrostatic weighing is more accurate than DXA) has also been reported (Bergsma-Kadijk et al.

1996; Goran, Toth, and Poehlman 1998; Millard-Stafford et al. 2001). In a review of DXA studies, Lohman and colleagues concluded that DEXA estimates of are within 1% to 3% of multicomponent model estimates (2000). Although some body composition prediction equations have been developed and validated with DEXA as the reference method, further research is needed before DEXA can be firmly established as the best reference method. Toombs and colleagues (2012), in their review of the metamorphosis of DEXA technology, support the call for additional research using 4C and human cadaver criterion measures before labeling DEXA as a gold standard for body composition assessment. Still, the DEXA method is widely used in light of its availability, ease of use, and low radiation exposure (Yee and Gallagher 2008). Regardless, caution is urged when interpreting the results of DEXA comparison studies given equivocal findings such as large intraindividual and significant group mean differences in body fat percentage compared to 4C measures (Toombs et al. 2012).

SECTION B

Methods

Skinfold Measurements

References: Adams, GM & Beam, WC. Exercise Physiology Laboratory Manual, 7th ed. New York, NY: McGraw Hill Education, 2014; American College of Sports Medicine. ACSM’s guidelines for exercise testing and prescription, 10th edition. Lippincott Williams & Wilkins 2018.

When taking skinfold measurements, consistency is important and inter-rater variability is a common problem that can limit the reliability of skinfold measurements. As a result, it is recommended that the same person perform future skinfold measurements to limit the variability. Research quality calipers, such as the Harpenden, Lafayette, and Lange, have scales that can be read with a range of 0.2 mm and 1.0 mm and should be used consistently to ensure the highest measurement accuracy. To further improve reliability, you should take measurements in duplicate while rotating through the measurement sites. For example, do not measure the abdomen two times in a row, but rotate through all measurement sites once, then do a second rotation of all the sites, and then a third (or fourth) rotation, if necessary. Finally, you will report the average of your triplicate measurements provide that they do not differ by more than 1-2 mm. NOTE: if the skinfold measurements differ by > 1-2 mm, then complete a third (or fourth) measurement at that site and take the average of the site measurements within 1-2 mm of each other. All skinfold measurements will be taken to the nearest 0.5-1 mm.

Skinfold Measurements Guidelines

Participants should wear loose-fitting clothing. Males are encouraged to go shirtless and females to wear a sports bra or swimsuit top.

All measurements should be made on the RIGHT side of the body.

Each skinfold site should be marked with a cross using a nontoxic marker as in figure 25.1 below.

Use a metric measuring tape to accurately determine the location of each site.

The calipers should be placed 1 cm away from the thumb and finger, perpendicular to the skinfold, and halfway between the crest and the base of the fold. Participants should keep muscles relaxed.

Pinch should be maintained while reading the gauge. Wait 1-2 seconds (NOT longer!) before reading caliper.

Take duplicate measures at each site and retest if duplicate measurements are not within 1 to 2 mm.

Rotate through measurement sites in a circuit to allow time for skin to regain normal texture and thickness.

Seven Standard Skinfold Measurement Sites and Techniques

Blue = 3-site skinfold measurement for males; Pink = 3-site skinfold measurement for females

A.Triceps skinfold measurement:

Fig. 25.1. Adams and Beam. (2014) Exercise Physiology Laboratory Manual 7th Ed; blue = 3-site skinfold measurement for males; pink = 3-site skinfold measurement for femalesSubject bends the right arm at a right angle keeping the elbow close to the side.

The measurement site is made at the midpoint of the acromion process (shoulder) and the olecranon process (elbow).

The subject lets the arm fall in the hanging position

With the thumb and index finger pointing downward, the tester grasps a vertical skinfold at the back of the arm, one centimeter above the mid-point.

The tester applies the points of the calipers to the back of the arm at this position.

B.Chest skinfold measurement:

Males: The site of this measurement is made halfway between the anterior axillary fold (front of the armpit) and the nipple.

Females: The site of this measurement is made 1/3 of the way between the anterior axillary fold (front of the armpit) and the nipple.

With the thumb and index finger pointing diagonally, the tester grasps a diagonal skinfold one centimeter above the measurement site.

The tester applies the points of the calipers to the long axis of the skinfold and makes the measurement.

C. Midaxillary skinfold measurement:

Participant places right arm on the shoulder of the tester.

Tester applies takes a vertical skinfold in the midaxillary line at a point horizontal to the xiphoid process.

The tester applies the points of the calipers to the long axis of the skinfold and makes the measurement.

D. Subscapular skinfold measurement:

The measurement site is made using an oblique fold just below the bottom tip of the scapula.

With the thumb and index finger pointing in an inferior direction the tester grasps an oblique skinfold just above the measurement site.

The tester applies the points of the calipers to the skinfold and makes the measurement.

E.Abdomen skinfold measurement:

The site of this measurement is made about 1 inch to the right of the umbilicus.

With the thumb and index finger pointing downward, the tester grasps a vertical skinfold one centimeter above the measurement site.

The tester applies the points of the calipers to the skinfold and makes the measurement.

F.Suprailiac skinfold measurement:

The site of this measurement is made just above the right illiac crest in the anterior or midaxillary line.

Place the arm of the participant on the shoulder of the tester. With the thumb and index finger pointing diagonally, the tester grasps a diagonal skinfold one centimeter above the measurement site.

The tester applies the points of the calipers to the long axis of the skinfold and makes the measurement.

G.Thigh skinfold measurement:

With the participant standing, all weight should be on the left leg to completely relax the right quadricep—place the skinfold caliper box or another object to slightly elevate the right heel of the participant to help completely relax the right quadricep.

The measurement site is made using a vertical fold over the quadriceps muscle on the midline of the thigh. The site is half the distance between the top of the patella and the inguinal crease.

With the thumb and index finger pointing in an inferior direction the tester grasps a vertical skinfold at the midline of the thigh one centimeter above the mid-point.

The tester applies the points of the calipers to the thigh at this position.

NOTE: Some of the locations can include sensitive areas, thus it is typically best to place yourself on the side of the subject when taking these measurements.

Calculation of Body Density and Body Fat Percentage from Skinfold Measurements (3-Site Jackson & Pollock Method)

Reference: Adams, GM & Beam, WC. Exercise Physiology Laboratory Manual, 7th ed. New York, NY: McGraw Hill Education, 2014.

The Jackson and Pollock methods use age and multiple skinfolds of a participant to estimate body density. Percent body fat is then determined from body density by using the Siri equation or other population-specific equations (see ACSM Table 4.3 provided below). Follow the steps listed to complete the calculation for each participant measured:

Calculate the average (AVG) values (2-3 measures within 1-2 mm) for EACH site. Record results in data table provided.

Determine the SUM of the average 3-site skinfold measures (e.g. Tricepaverage + Suprailiacaverage + Thighaverage). Record results in data table provided.

Use gender-specific formulas below to calculate body density (Db) for EACH of the participants measured. Record results in the data table provided. SSF = Sum of the average three-site skinfold measures (mm).

Db (Males) = 1.10938 – (0.0008267 * SSF) + [0.0000016 * (SSF)2] – (0.0002574 * Age) Db (Females) = 1.0994921 – (0.0009929 * SSF) + [0.0000023 * (SSF)2] – (0.0001392 * Age)

Use Siri equation to convert body density values to body fat percentage (BF%) for EACH of the participants measured. Record results in the data table provided.

% Body Fat Siri Equation = [(4.95 / Db) – 4.50] ∗ 100

Use the table of population specific equations (ACSM Table 4.3) to also convert body density values to body fat percentage (BF%) for EACH of the participants measured. REMEMBER: Multiple your final value by 100 for body fat percentage value. Record results in the data table provided.

Dual Energy X-Ray Absorptiometry (DEXA) Testing Guidelines and Procedures

Reference: Heyward, VH & Gibson, AL. Advanced Fitness Assessment and Exercise Prescription, 7th ed. Champaign, IL: Human Kinetics, 2014.

DEXA equipment calibration and standardization procedures should be completed by the laboratory staff prior to participant testing.

Participants will remove all metal, ceramics, jewelry, shoes, and any clothing that contains metal-based buttons/zippers or reflective components. Supplemental clothing is available for participants who need to change out of their street clothes.

Require participants to complete void the bladder and bowels BEFORE beginning the test.

Measure the participant’s height using a stadiometer to the nearest cm. The participant’s demographic and basic anthropometric measurements are entered into the DEXA software.

The participant will lie supine on the DEXA table and will be positioned by the laboratory staff ensuring that the top of the head touches the top line of the DEXA scan field. The participant will be centered within the scan field striped on the DEXA table with the central line bisecting the participant’s body. Arms will be placed alongside the body with ample distance between the torso and the arm. Hands will be placed flat on the DEXA table if enough space is available within the DEXA scan field. If there is not enough space is available, the hands will be positioned vertically with pinky finger down so that there is still ample space between the torso and arm. Feet will be internally rotated and strapped together to maximize the femoral surface area exposed in the scan field.

Once positioned, the participant MUST remain completely still over the duration of the scan.

After the scan is complete, the laboratory staff will fine tune the scan assessment by the DEXA software by manually manipulating the scan regions.

The final scan report will be printed and available for viewing.

SECTION C

General Laboratory Notes

In continuation of the in-class discussion, you will complete the following questions and tasks listed below.

GOAL OF THIS LAB: To understand appropriate skinfold measurement and DEXA testing protocols as they relate to exercise metabolism, nutrition, and body composition evaluation.

EACH STUDENT will complete the lab write-up provided below based on their reading, research, previous knowledge, and consultation with other classmates.

SECTION D

Skinfold and DEXA Lab Worksheet

Include this sheet in your lab write-up due at the beginning of your next class. NO late work accepted.

Place your data in the tables provided. On these page(s) SHOW ALL YOUR WORK IN AN ORGANIZED MANNER. If you do not show any work, you will not receive any credit.

Student names MUST remain anonymous. Sharing of any lab information outside of the laboratory classroom is STRICTLY PROHIBITED and will be deemed a violation of The George Washington University Honor Code. Please respect the privacy and confidentiality of your lab team, classmates, and peers.

Student Name: Lab Partner 1: Age:26 yrs.

Date:

Lab Partner 2:

DATA TABLE 1: Demographics, Anthropometrics, & BMI Measures

Student

Sex

Hours

Fasted

Last Exercise

(hrs. ago)

Stress Level

(circle one)

Age

(yrs.)

Platform

Wt. (lbs)

Platform

Wt. (kg)

Ht.

(in)

Ht.

(cm)

BMI

(kg/m2)

M / F

High / Medium / Low

132

69.0

174

19.7

NOTE: The platform scale and stadiometer will be used to measure body weight and height.

Blank Area for Calculations:

DATA TABLE 2a: 3-Site Skinfold Measures (Student [YOUR OWN] Personal Data)

Measurement

Trial #

MALE:

Chest (mm)

MALE:

Abdomen(mm)

FEMALE:

Triceps (mm)

FEMALE:

Suprailiac (mm)

BOTH:

Thigh (mm)

3 (if necessary)

4 (if necessary)

3-Site SUM:

AVG

NOTE: MALE = male measurement site only; FEMALE = female measurement site only; BOTH = measurement site all individuals; AVG = average of measurements 1-2 (or whichever 2 sites are within the 1-2 mm requirement); SUM = summation of all 3 site AVG measures (for the participant’s gender); at least 2 measurements must be conducted for each of the sites listed with NO MORE THAN 1-2 mm difference between measurement trials—the average measurement should be calculated across the 3 closest measures

DATA TABLE 2b: 3-Site Skinfold Measures (Student 1 Data)

Measurement

Trial #

MALE:

Chest (mm)

MALE:

Abdomen(mm)

FEMALE:

Triceps (mm)

FEMALE:

Suprailiac (mm)

BOTH:

Thigh (mm)

3 (if necessary)

4 (if necessary)

3-Site SUM:

AVG

DATA TABLE 2c: 3-Site Skinfold Measures (Student 2 Data)

Measurement

Trial #

MALE:

Chest (mm)

MALE:

Abdomen(mm)

FEMALE:

Triceps (mm)

FEMALE:

Suprailiac (mm)

BOTH:

Thigh (mm)

3 (if necessary)

4 (if necessary)

3-Site SUM:

AVG

18.5

15.5

DATA TABLE 2d: 3-Site Skinfold Measures (Student 3 Data)

Measurement

Trial #

MALE:

Chest (mm)

MALE:

Abdomen(mm)

FEMALE:

Triceps (mm)

FEMALE:

Suprailiac (mm)

BOTH:

Thigh (mm)

3 (if necessary)

4 (if necessary)

3-Site SUM:

AVG

DATA TABLE 3: Circumference/Girth Calculations, BIA & Skinfold Measures

Student

Naval Health Method Siri BF %

3-Site Skinfold BF% (Siri)

3-Site Skinfold BF%

(Pop. Specific)

In-Body BF%

DXA BF%

BF% Diff: SKFsiri vs. SKFpop

BF% Diff: Naval vs. SKFsiri

BF% Diff: In-Body vs. SKFsiri

BF% Diff: DXA vs. SKFsiri

Personal

7.57

11.5

19.90

18.3

27.3

36.8

21.4

24.2

NOTE: BF% = body fat %; Naval Health BF% and In-Body values should be carried over from the first week’s lab (Lab #4).

Blank Area for Calculations:

DATA TABLE 4: DEXA Scan Results (Student [YOUR OWN] Personal Data)

Student

BMD

(g/𝐜𝐦𝟐)

BMD

z-score

BMC

(lbs)

LBM

(lbs)

Fat Mass

(lbs)

BF%

Classification

VAT

(lbs)

A/G Ratio

NOTE: BF% = body fat %, BMD = bone mineral density, BMC = bone mineral content, LBM = lean body mass, VAT = visceral adipose tissue, A/G Ratio = android/gynoid ratio

DATA TABLE 5: DEXA Segmental Results (Student [YOUR OWN] Personal Data)

Total (lbs)

Total (%)

Arms (lbs)

Arms (%)

Legs (lbs)

Legs (%)

Trunk (lbs)

Trunk (%)

Fat

Lean

BMC

Difference

NOTE: BF% = body fat %, BMC = bone mineral content

Resting Metabolic Equations (can be used as a reference for your answers):

Cunningham (1991): 370 + (21.6 x FFM)

Mifflin et al. (1990): (9.99 x Wt) + (6.25 x Ht) – (4.92 x Age) +5

Blank Area for Calculations:

Lab Tasks:

Using the instructions provided above, work to test/measure AT LEAST three (3) classmates using the three (3)- site skinfold method. You will also include the specific trials of YOUR PERSONAL skinfold measures in the table provided above. (5pts)

Using the information provided in the lab packet, calculate the required information in EACH of the data tables based upon the measurements collected. Show your calculations in the space provided. (5pts)

Create a bar graph comparing your PERSONAL SEGMENTAL measurements from the DEXA and INBODY results. (Both arms, both legs, trunk, total) Compare Body Fat % measured in these areas. (5pts)

Using the skin fold measurements from the class excel file, create a bar graph that compares FIVE (5) sites of skin fold measurement data (male + female sites) of your personal measurements and THREE (3) classmate’s measurements. (5pts)

Lab Questions:

Based on your experience in lab, what are the primary challenges (list AT LEAST 3) that practitioners or clinicians could face when assessing skinfold measures on patients or clients? Were there any personal challenges or difficulties that you faced while collecting skinfold data in lab? How did you overcome these challenges or difficulties? Explain. (3pts)

The DXA results provide resting metabolism data. Is the equipment actually measuring this component? If not, how is this information formulated or calculated and is this data reliable? Explain. (2pts)

How can skinfold measurements be used to track an individual’s body composition changes without calculating body density or body fat percentage? Would this method increase or decrease the error associated with this body composition method? Explain. (2pts)

Search the current literature to explain why DXA is the gold standard measurement method for body composition. Has DXA always been considered the gold standard for body composition measurement? Is DEXA the proper body composition measure for infants and children? If not, what is the standard body composition measure in this population? Lastly, how is DXA being implemented as part of a 4-component body composition model in the more recent body composition literature (HINT: you may want to search for this topic associated with a researcher from UNC-Chapel Hill, Dr. Abby Smith-Ryan). (3pts)

EXNS 2111: Lab 5—Body Composition II – Skinfold & DEXA

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