4

Body Composition

chapter

Rationale for measuring body composition

• To assess the decrease in body fat weight that occurs in response to a weight management program.

• To help athletes determine the best body composition for performance.

• To monitor fat and fat-free weight in patients with disease.

• To track long-term changes that occur in body fat and fat-free mass with aging.

Fat mass

Important Terms

Fat-free massPercent body fatObesityOverweightBody fat distribution, or fat patterningAndroid-type obesityGynoid-type obesityAnthropometry

Body Composition = ratio of fat to fat-free mass.

Comparison of 2- and 4-compartment models

Reference proportions for 4-compartment model.

Height and Weight• Does not differentiate between fat-free and fat-mass.

Weight measurement alone cannot accurately determine

body fat status

•People vary widely in somatype (or body build)

The 1983 Metropolitan Height-Weight Table has multiple deficiencies and is no longer

recommended. (p. 45 ACSM)

In older epidemiological studies, obese was defined as 20% or more overweight using the concept of relative weight (now

rarely used because it was replaced by the BMI):

[(body weight/midpoint value of weight range) x 100]

The table below summarizes standards for relative weight.

Measuring Weight and Height

• Body weight should be measured on a physician’s balance-beam scale with minimal clothing and no shoes.

• Height should be measured with a stadiometer:– No shoes, heels together, back

straight, heels, buttocks, shoulders, and head touching the wall, standing as tall as possible, and looking straight ahead.

– Have individual inhale deeply and hold breath.

Frame size can be estimated by measuring the width of the elbow. The table below shows how elbow breadth can be classified as small,

medium, and large frame (according to the Metropolitan Life Insurance Company, as used with their 1983 height-weight table).

Also see Table 4-1C for Frame size classifications.

Body mass index (BMI) is a commonly used estimate of obesity (especially in population studies and surveys). The Quetelet Index is the most popular BMI estimate: kg/m2

The table below shows the relationship between BMI and percent body fat (r=0.70, SEE 5% body fat).

The table below summarizes the 1998 NHLBI Obesity Education Initiative guidelines for classifying BMI, with disease risk estimated when also related to waist circumference. (Also see CDC growth charts that classify BMI for boys and girls, aged 2-20 (my website: pdf documents)http://www.cdc.gov/nccdphp/dnpa/bmi/childrens_BMI/about_childrens_BMI.htm

Body mass index (BMI) is a commonly used estimate of obesity

(especially in population studies and surveys). The Quetelet Index is the most popular BMI estimate: kg/m2

Assume that body is divided into fat and fat-free mass.Assume a constant density of fat and fat-free tissues among individuals.Siri (1961) gives a common model: %BF = 495/Db – 450.

Two-Compartment Models

When components of the fat-free mass differ from the assumed values, estimation of %BF is compromised.There are two-compartment models for various populations.Both hydrostatic weighing and air displacement plethysmography use two-compartment models.

Often referred to as a criterion methodBased on Archimedes’ principleUsed to calculate total body density

Hydrostatic Weighing

Db = BW

(BW – UWW)

D – RV

H2O

Density of Water

Air displacement plethysmography (BOD POD). (based on the two-compartment body composition

model).

Electrical current travels more easily through tissue containing water and electrolytes.Fat does not contain much water; therefore, electrical flow is impeded.Fat can be estimated by the impedance encountered when electrical currents pass through the body.

Bioelectrical Impedance Analysis (BIA)

(continued)

Leg-to-Leg BIA (Tanita Corporation)

There are a number of commercially available BIA devices.

Values are typically within 4% of those obtained with hydrostatic weighing.

It is important to choose the proper equation for estimating %BF.

It is critical that person being tested is normally hydrated.

Tetrapolar BIA technique

Skinfold Measurements

The most widely used body composition estimate is the skinfold measurement technique. When performed correctly, skinfold measures provide an fairly good estimate of percent body fat (r>/=0.80 with underwater weighing). As shown below, the goal is to measure a double fold of skin and subcutaneous tissue (with sides of skinfold approximately parallel). The thicker the fat layer, the wider the fold.

Skinfold Measurements

To make the measurements as accurate as possible,

Accuracyin Measuring Skinfolds

accurately locate the skinfold site,accurately measure the skinfold, andchoose the appropriate equation for converting skinfold thickness into %BF.

Basic Rules for Taking Skinfolds

• Take skinfold measurements on the right side of the body (most skinfold equations were developed from measurements on the right side).

• Do not take measurements when the subject's skin is moist (ensure that the skin is dry, and has no lotion). Also do not take measurements immediately after exercise or when the person being measured is overheated because the shift of body fluid to the skin will inflate normal skinfold size.

• To reduce error during the learning phase, skinfold sites should be precisely determined, marked, and verified by a trained instructor. The largest source of error in skinfold testing is inaccurate site selection.

Skinfold Rules (continued)

• Firmly grasp the skinfold with the thumb and index finger of the left hand, and pull away.

• Hold the caliper in the right hand, perpendicular to the skinfold and with the skinfold dial facing up and easily readable. Place the caliper heads ¼-½ inch away from the fingers holding the skinfold. Try to visualize where a true double-fold of skin thickness is, and place the caliper heads there.

• Read the caliper dial to the nearest 1 millimeter within 4 seconds. During the measurement, ensure that the left thumb and forefinger maintains the shape of the skinfold.

• Take a minimum of 2 measurements at each site (at least 15 seconds apart). If the 2 values are within 10% of each other, take the average.

Thigh Skinfold Vertical fold on anterior thigh, midway between

inguinal crease and proximal border of patella.

Suprailiac Skinfold

Jackson-Pollock procedure: a diagonal fold is taken with the natural angle of the iliac crest

at the anterior axillary line immediately superior to the

iliac crest.

Chest SkinfoldJackson-Pollock procedure: the chest/pectoral skinfold site is one

half the distance between the anterior axillary line and the nipple for men, and one third of this distance for women.

Triceps Skinfold

Vertical fold on posterior aspect of arm, midway between lateral projection of

acromion process and inferior margin of olecranon process.

Abdomen Skinfold Site Jackson-Pollock procedure uses a vertical fold 2 cm to

the right of the umbilicus.

Subscapular Skinfold

Diagonal fold just below the inferior angle of scapula.

Midaxillary Skinfold

Jackson-Pollock procedure, a vertical

fold taken on midaxillary line at level of xiphoid/sternal

junction.

Medial Calf

A vertical skinfold on the inside of the calf at the level of maximum

circumference.

Body fat standards for children/youth ages 6-17 years using the triceps and subscapular skinfolds (sum).

Body fat standards for children/youth ages 6-17 years using the triceps and medical calf skinfolds (sum).

Jackson and Pollock generalized body composition equations (Box 4-2, p. 65)See Table 4-6 (ACSM p. 68) for age- and sex-specific equations to convert body

density to percent body fat.

The Brozek (457– 414.2 /body density ) and Siri (495– 450 /body density ) equations estimate percent body fat from body density. Fat

free mass varied among different groups, and Table 4.6 ACSM p. 68 summarizes recommended equations.

Nomogram for estimating

percent body fat from sum of

three skinfolds.

Durnin and Womersley equations for calculating body density (based on sum

of 4 skinfolds---biceps, triceps, subscapula, and suprailiac).

Use Table 4.6 for age- and sex-specific equations to convert body density to percent

body fat.

Biceps skinfold = vertical fold on anterior upper arm directly opposite triceps skinfold site.

Body Fat Ranges for Ages 18 and Older

Classification Male Female

Unhealthy range (too low) <5% <8%

Acceptable range (lower end) 6-15% 9-23%

Acceptable range (higher end) 16-24% 24-31%

Unhealthy range (too high) >25% >32%

Average Body Fat Ranges for Elite Athletes

Males Females

Endurance Athletes 4-15% 12-26%

Athletes in Sports that

Emphasize Leanness 4-10% 10-19%

Team/Dual Sport Athletes 7-21% 18-27%

Power Athletes 5-20% 17-30%

Waist: Most narrow part of the torso between the xiphoid process and the umbilicusAbdomen: Circumference of the torso at the level of the umbilicusHips: Maximal circumference of the buttocks above the gluteal fold

Girth Measurements:Important Measurements

Thigh: Largest circumference of the right thigh below the gluteal fold

The ratio of waist-to-hip circumference (WHR) has

been used to determine android vs. gynoid type of

obesity.

The waist circumference alone is more commonly

used than the WHR.

A waist-to-hip ratio of more than 0.94 for men or 0.82 for women is considered too high.

A waist circumference greater than 102 cm in men or 88 cm in women significantly increases the risk of obesity-related disease.

It is often important to help clients determine a healthy and reasonable weight. Calculating target body weight requires knowledge of current body weight, %BF, and desired %BF.

Calculating Target Body Weight

Target body weight = FFM

Desired %BF

1001 –( )