Body Composition Assessment

A description of assessment methods.

Body Composition

The relative % of body weight that is fat and fat-free tissue

Why measure body comp?

Health Implications– there is an ideal % fat for health reasons

(prevent onset of diabetes, CHD, BP, etc…) Make BW recommendations

– can use % fat values to determine an ideal BW

– how much fat to lose versus how much muscle to gain

Height - Weight Tables

Body composition is a better indicator of fitness than body weight/height. Standard height-weight tables do not provide accurate estimates of what you should weigh because they do not take into account the composition of the weight. A subject can be overweight according to these tables yet have very little body fat.

For example:

Body Builder:– 5’5”– 200 pounds– overweight according to height/weight

tables– 4% body fat– ALL MUSCLE!!!

Fat Mass vs. Fat-free Mass

Two Component Model

Fat-free mass is composed of all of the body's nonfat tissue including bone, muscle, organs, and connective tissue. Fat mass includes all the body’s fat along with essential fat.

Essential Fat

All fat is not bad!! We need fat for padding of organs,

insulation, energy source There is a minimum amount that we

need to function daily = essential fat Gender specific

– males ~ 3%– females ~ 7%

Essential Fat

Why the differences?– A male at 7% is like a female at 17%– Women are more complicated!!– Women have babies, menstrual cycles,

etc… and need more fat for the survival of the species

Methods

1. Under Water Weighing (Hydrodensitometry)

2. Bioelectrical Impedance (BIA) 3. Dual-Energy X-ray Absorptiometry

(DEXA) 4. Near-Infrared Interactance (NIR)

Methods

Anthropometric Measures (anthro=body; metric=measuresbody measurements)

5. Skinfolds 6. Circumference (WHR) 7. Diameters (body typing) 8. Height (BMI) 9. Others…..??

Hydrodensitometry

Used to be considered the most accurate (up for debate now that DEXA is used)

+2.5% if done with experienced subjects

UWW

Fat Component - Fat (adipose)+Neural+Essential Fat– density of 0.9 g/ml

Fat-Free Component - muscle+bones+ tendons+organs– density of 1.10 g/ml

UWW

Water Density ~ 1.0 g/ml (temperature of the water affects the density)

Thus, if more fat will float (fat is less dense than water)

If more muscle will sink (muscle is more dense than water)

Procedures

1. Wear light clothing (swimsuit) 2. Use bathroom prior to weighing 3. Calibrate scale 4. Weight the chair or seat and

equipment 5. Measure water temp 6. Remove all air from clothing

Procedures

7. Sit in seat 8. Submerge 9. Blow all air out of lungs and remain

still 10. 3-10 trials; average of the highest

three 11. Subtract weight of apparatus from

average UWW

Equations

% fat = 457÷BD - 4142 %fat = 495÷BD - 450

Sources of Error

Not getting all air out Reading scale wrong Are not using the correct equation Estimation of RV

BIA

Based on the premise that fat-free tissue is a better conductor of an electrical current (contains water and electrolytes) than fat tissue

The resistance to current flow is inversely related to FFM

BIA

Abstain from eating or drinking for 4 hours prior

No exercise 12 hours prior No alcohol 48 hours prior No diuretics (caffeine) prior to

assessment

Advantages

Non-invasive Safe Easy to administer Accurate on some populations Field technique

Disadvantage

The accuracy has been questioned:– Skinfolds 2.4 % error– BIA 5% error– Visual 3.1% error

Race cannot be entered into the machine

Children distribute water differently than adults

NIR

Based on the premise that the degree of infrared light absorption is related to the composition of the substance through which light passes

Fat and Fat-Free Mass absorb and reflect light differently

Advantages

Non-invasive Safe Easy to administer Field technique

Disadvantages

Cost? Is it worth it? Few Age/Gender Specific Equations Accurate?

– Futrex 5000 3.1-4.2%– Futrex 5000A 6.3%– Futrex 1000 4.8-6.3%– Sum 3 2.4-3.6– BIA 5.0-7.1%

Skinfolds

Measurement of subcutaneous adipose tissue at specific anatomical sites

BD or %fat is obtained with the use of equations (either population specific or generalized)

SF Procedures

Take all measurements on the right side of the body

Identify and mark site Grasp skin and fat between thumb and

index finger 1cm above marked site Continue grasping at the site while

taking the measurement

SF Procedures

Take at least 2-3 non-consecutive measurements - if values vary by +2mm take additional measurements

No measurements directly after exercise

Sites

Chest Subscapular Midaxillary Suprailiac Abdominal Triceps Biceps Thigh Calf

Equations

Jackson’s 3-site– Males - BD=1.10938-

0.0008267(sum3)+0.0000016(sum3)2-0.0002574(age)

– chest, abdomen, thigh– Females - BD=1.0994921-

0.0009929(sum3)+0.0000023(sum3)2-0.0001392(age)

– triceps, suprailiac, thigh

Skinfolds

Use text table 4.1, 4.2, 4.3, 4.9

Circumferences

1. Waist to Hip Ratio 2. Determination of Body Comp

Waist to Hip Ratio

Indication of the pattern of body fat distribution

Indicator of the health risks of obesity– excess trunk fat - increased risk of

hypertension, type 2 diabetes, high cholesterol, CAD, premature death

Measurements

Made with a tape measure Waist - at the level of the umbilicus Hips - biggest part of the gluteals

Waist to Hip Ratio

Risks increase with increasing ratios Men

– Very low risk <.95– Low risk .96-.99– High risk >1.00

Waist to Hip Ratio

Risks increase with increasing ratios Women

– Very low risk <.80– Low risk .81-.84– High risk >.85

Determination of Body Comp

Figure 4.5 and Table 4.4, 4.9

Body Mass Index (BMI)

Ratio of a person’s weight (kg) to the height squared (m2)

Used to categorize people with respect to their degree of obesity

Not used to determine % fat Table 4.7 and Table 4.8

BMI

<20 - underweight 20-25 kg/m2 - acceptable 25-29.9 kg/m2 - overweight >30.0 - obesity

Calculations for Optimal BW

1. Determine % fat 2. Calculate Fat Weight

– BW * %fat ÷ 100 3. Calculate Fat-Free Weight

– BW - FW 4. Calculate Desirable Weight

– FFW ÷ (1- (desired %fat ÷ 100))

Calculations

5. Calculate amount of weight that needs to be lost– BW - Desirable Weight

6. Calculate kcal deficit– 3500 kcal per pound of weight needed to be lost

7. Assuming loss of 1 pound (3500 kcals) per week, calculate # weeks to reach goal

Assignment

Lab 4B