8 Chapter 8: Estimating body composition

Melissa Markofski

Background

Body composition and anthropometric measures

There are many ways to assess body composition and anthropometric measures. Some of these methods require expensive, highly specialized equipment, while other methods are simple and use inexpensive equipment. When evaluating a person’s progress and taking measurements before, during, and after a training program, the method does not matter as much as using the same method for all timepoints and being accurate (reliable) in your measurements. 

Anthropometric measures are: height, weight, BMI, body circumferences, and skinfold thickness. It is important to make the distinction that skinfold thicknesses are anthropometric measures, but when the skinfold thickness measures are used to calculate an estimation of body fat then body fat measurement is not an anthropometric measure.

Anthropometric measurements are simple, easy measurements that can help additionally classify a person’s health. The waist to hip ratio is calculated from measurements of the circumference of the waist (narrowest point of midsection) and hips (widest circumference around pelvis). A ratio of greater than 0.95 for males and 0.86 for females is considered an increased risk for CVD.

Circumference anthropometric measurements can also be used to track fitness. It can be used as a crude estimate of fat loss and/or muscle gains. These measurements are typically taken around the belly of the muscle group of interest, such as the thigh or upper arms.

Regardless of the method for assessing body composition, each method is estimating body composition. We are not physically dividing the body into lean mass and non-lean mass and weighing it. Care also needs to be taken to decide if the estimated body composition measures should be expressed as absolute or relative values.

 

Class activity

Estimated body composition

Activity 1: Air displacement plethysmography (BodPod GAR 110)

Air Displacement Plethysmography (ADP) measures body volume and body density to estimate body composition.

Video #1: BodPod Demonstration

Virtual Lab Activity 1
Watch a demonstration of a BodPod measurement:
1. Watch the video above.

 

Activity 2: Bioelectrical impedance (BIA)

BIA uses resistance of an electrical current to estimate body composition. Muscle contains more water than adipose tissue, and therefore muscle will resist the electrical current less than adipose tissue. However, hydration status is an important factor in obtaining an accurate measurement.

To use the BIA, you will need to be barefoot. The machine will walk you through the input.

1) Turn on unit with on/off button

2) Enter clothes weight (typically 2 lbs)

3) Enter sex and body type by pressing the corresponding key. Use “athletic” if you are involved in at least 10 hours of intense physical activity a week, or have a lifetime of fitness (have had this level of activity for 5+ years, but are not presently reaching this amount of activity).

4) Enter age, in years

5) Enter height in feet then inches

6) Step on scale and be still until the unit prints your results.

7) Clean the scale (spray paper towel with cleaner—not the BIA!—and wipe the contacts).

Video #2: Demonstration of Body Fat Analysis (BIA) Scale and Measurement

  • This video is an example of one brand of BIA, but it covers the procedure and measurements that will be similar for most brands. You only need to watch the first ~4 minutes.

Virtual Lab Activity 2
Watch a demonstration of a BIA scale measurement:
1. Watch the video above.

 

Activity 3: Skinfold calipers

Skinfold calipers can also be used to calculate relative body fat. For this lab we will use the three site method, with specific locations for males or females. You will need to review the “How to Measure Skinfolds” box on page 194 of your text.

 

  1. Collect measurements of basic body dimensions (height and weight)
  2.  Use the skinfold calipers to measure skinfold thickness (mm). For men measure chest, abdomen, and thigh. For women measure triceps, suprailiac crest, and thigh.
  3. Collect each measurement three times from each site (rotate sites i.e. collect all of the three sites once, then again, then a third time).
  4. Use your textbook table 7.7 to refresh your memory of where the specific sites are located, paying attention to the orientation of the measurement (horizontal, diagonal, etc.).
  5. Calculate body density (sum3 = sum of the three skinfold sites)

 

Calculation of body density (Db) to 5 significant figures:

Skinfold Thickness (Jackson & Pollock):   Db= _______________gm/cc

males = 1.109380 – (0.0008267 x sum3) + (0.0000016 x sum32) – (0.0002574 x age)

Females = 1.0994921 – (0.0009929 x sum3) + (0.0000023 x sum32) – (0.0001392 x age)

 

6. Calculation of relative body fat (Siri) males: (495 / Db) – 450 = ________%

Calculation of relative body fat (Siri) females:  (509 / Db) – 450 = ________%

7.Calculation of fat weight (FW): body weight  x  % fat

8. Calculation of fat free weight (FFW): body weight – fat weight

9. Calculation of optimal or desirable body weight:

Target body weight = current absolute fat free weight /  target relative FFM%

Hint: absolute fat free weight is in kg and goal relative FFM is expressed as <1.0

Video #3: Example of seven site skinfold body fat measurements

  • Video of the seven sites for skinfold measures. Your lab manual is three sites, with different sites for men and women. This seven site video uses all the sites, and has some excellent information on the methods for this measurement.

Virtual Lab Activity 3
Watch a demonstration of skinfold body fat measurements:
1. Watch the video above.
Practice Calculations:
1. Practice body density, relative body fat, FM, and FFM. Check your answers in the box below.
Practice Calculations (Skinfold Measure Case #1):
You measure skinfold thickness for three sites on a 21 year-old female. Height=163cm, weight=62.5kg, thigh skinfold=15mm, suprailliac skinfold=12mm, and triceps skinfold=23mm.
1. Calculate body density (Db) to 5 significant figures (Jackson & Pollock).
2.  Calculate her relative body fat % (Siri).
3. Calculate her fat weight (FW).
4. Calculate her fat free weight (FFW).
5. If she would like to lose 5 percentage points of her current relative fat percentage, what is her target body weight to reach this goal?

 

Anthropometric measurements

Activity 4:  circumference measurements

Use your textbook Table 7.3 to refresh your memory of how to conduct this measurement.

  1. Take each measurement on you or a family member/friend twice. Collect measures of waist, hip, thigh, and upper arm.
  2. If the sites differ by more than 2 cm, take a third and average the two within 2 cm.
  3. Use the averages of the hip and waist to calculate the waist:hip ratio

 

Virtual Lab Activity 4
Practice performing circumference measurements:
1. Measure and calculate the waist:hip ratio on yourself or a family member/friend.
Practice Calculations:
1. Practice waist:hip calculations. Check your answer in the box below.
Practice Calculations:
A 25 year old male has a waist measurement of 72cm and a hip measurement of 90cm.
1. What is his waist:hip ratio?
2. Using table 7.4 in your textbook. What risk category does this place him in?

Comparisons

Activity 5: Coefficient of variation

There can be much variation in methods. The coefficient of variation is expressed as a percent and can help us determine the repeatability of the measurement (and precision).

coefficient of variation of sample = (standard deviation of sample) / (mean of sample)

Note: standard deviation of sample = square root of [(the variance) / (n-1)]

\sigma={\sqrt {\frac {\sum _{i=1}^{n}\left(x_{i}-{\bar {x}}\right)^{2}}{N-1}}}

where n = number of samples

variance =  add the squares of each difference between each sample and the mean

Virtual Lab Activity 5
Practice Calculations:
1. Practice calculating the coefficient of variation. Check your answer in the box below.
Practice Calculation:
You measure a subjects body fat % with three different methods and found: BIA=23.0%, BodPod=15%, and skinfolds=21%. What is the coefficient of variation for these 3 measures?

Additional Practice Calculations

Body Composition Calculation (Skinfold Measure Case #2):
You measure skinfold thickness for three sites on a 25 year old male. Height=185cm, weight=85.7kg, thigh skinfold=12mm, abdominal skinfold=8mm, and chest skinfold=13mm.
1. Calculate body density (Db) to 5 significant figures (Jackson & Pollock).
2.  Calculate his relative body fat % (Siri).
3. Calculate his fat weight (FW).
4. Calculate his fat free weight (FFW).
5. If he would like to lose 2 percentage points of his current fat percentage, what is his  target body weight to reach this goal?
Coefficient of Variation Calculation:
You measure a subject’s relative body fat (%) with three different methods and found: BIA=32.0%, BodPod=25.0%, and skinfolds=23.0%. What is the coefficient of variation for these 3 measures?