# Body Composition Assessment

## Presentation on theme: "Body Composition Assessment"— Presentation transcript:

Body Composition Assessment
A description of assessment methods.

Learning Objectives Differentiate among body build, body size, and body composition. Discover how densitometry and several field techniques are used to assess body composition. Find out what tissues of the body constitute fat-free mass

Learning Objectives Calculate changes in FW and FFW with a weight loss program Find out what guidelines best determine an subject's goal weight.

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

Why measure body comp? Health Implications Make BW recommendations
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

Why measure body comp? Describe Athletic Populations
swimmers are more fat (fat floats) wrestlers/gymnasts want less fat endurance runners don’t want massive amounts of muscle but power lifters do

Height - Weight Tables Body composition is a better indicator of fitness than body weight/height. Being overfat (not necessarily overweight) has a negative impact on exercise/athletic performance. 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.

Assumptions of Two-Component Models
1. The density of fat is g/ml 2. The density of FFM is g/ml 3. The densities of fat and FFM are the same for all individuals

Assumptions 4. The densities of the various components of FFM are constant within an individual 5. The individual being measured differs from a reference body (73.8% water, 19.4% protein, 6.8% mineral) only in the amount of fat

Fat Depots 1. Subcutaneous 2. Intermuscular 3. Intramuscular
4. Abdominal and Thoracic Cavity

MODELS OF BODY COMPOSITION

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

Other Models We can’t distinguish between fat that is essential and fat that is not so in order to have more components in a model: we break the fat-free mass down further (referred to as a multi-component model) ie., 3-component model (fat, water, solids) ie., 4-component model (fat, water, mineral, protein)

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=measuresbody 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 Considered a lab technique (can’t carry your tank with you out into the field) Two-component Model

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)

Hydrodensitometry BD = BW/BV Body weight = measured on a regular scale
Body volume = measured using hydrostatic (underwater) weighing accounting for water density and air trapped in lungs

UWW Body Density = BW÷((BW-UWW)/H20 Density) - RV-0.1

UWW Determine BV  Calculate BD  Calculate %fat
If have high BV  low BD  more fat If low BV  high BD  less fat

UWW Archimedes principle - an object (or human) immersed in fluid, loses an amount of weight equivalent to the weight of the fluid that is displaced More simply - fill a bathtub with water - submerge - if catch all the water that spills over and weight it = BV

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 trials; average of the highest three 11. Subtract weight of apparatus from average UWW

UNDERWATER WEIGHING TECHNIQUE

Residual Volume Cannot blow all of the air out of your lungs (that would be bad!!) We need to account for the air that is left in the lungs (RV) + the air in the GI (~0.1L)

Determining RV Prediction equations based on height and/or Vital Capacity Male = 0.24 x VC Female = 0.28 x VC Male = 0.019(Ht cm) (age)-2.24 Female = 0.023(Ht cm)+0.021(age)-2.978 Nitrogen Analysis (rebreathing apparatus)

Equations Inaccuracies in hydrodensitometry are due to variation in the density of the fat-free mass from one individual to another. Age, sex, and race affect the density of fat-free mass. Thus, we have age/gender/race/fat specific equations - Table 4-1 Guidelines

Equations % fat = 4.57÷BD - 4.142 * 100 ACSM guidelines:

Many equations that are specific to each group

Disadvantages Most subjects not comfortable blowing all their air out
especially hard for children to understand methods to compensate for this Ambulatory problems (ie., elderly) getting into a pool/tank Some people just do not like water

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

Assumptions 1. The human body is a perfect cylinder with uniform length and cross-sectional area 2. The impedance to a current is directly related the length of the conductor and inversely related to its cross-sectional area

Assumptions 3. Biological tissues act as conductors or insulators, and the flow will follow the path of least resistance 4. Impedance is a function of resistance and reactance (opposition to flow caused by the capacitance of a cell membrane)

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

Equations Each machine has its own equation (developed by the manufacturer and is proprietary) %fat = 4.57 ÷ ( ((BW * Resistance) ÷ Ht2)) * 100 ht = length of the conductor

BIA Reseach Equations Population-specific equations have been developed through research Used for children, different races, different ages etc… (p. 161) May have better accuracy than machine equations

Accurate on some populations Field technique

Advantages More costly than SF calipers
Many studies have begun to cross-validate (just because the equation worked on the researchers population doesn’t mean it will work on others) Beginning to develop specific equations get resistance value from machine and enter into a specific equation

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

DEXA 3 component model assesses total bone mineral content
bone, fat, fat-free mass assesses total bone mineral content usually found in a clinical setting

Advantages Accurate Measurement of bone content (osteoporosis) safe
rapid minimal subject cooperation (just lay there)

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

NIR Emit infrared light at wavelengths of nm into a body part (ie., biceps) and measures the intensity of the re-emitted light More specific equations/machines are necessary

Disadvantages Cost? Is it worth it? Few Age/Gender Specific Equations
Accurate? Futrex % Futrex 5000A 6.3% Futrex % Sum BIA %

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 Place the jaws of the caliper perpendicular to the fold and slowly release the pressure Take the measurement 4 seconds after pressure is released Read the dial of the nearest 0.1mm (Harpenden or Holtain), 0.5mm (Lange), or 1mm (plastic)

SF Procedures Take at least 2 non-consecutive measurements - if values vary by +10% take additional measurements No measurements directly after exercise Reliability should be 0.95 or greater

Sites Chest Subscapular Midaxillary Suprailiac Abdominal Triceps
Biceps Thigh Calf

Equations Jackson’s 3-site
Males - BD= (sum3) (sum3) (age) chest, abdomen, thigh Females - BD= (sum3) (sum3) (age) triceps, suprailiac, thigh

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

Waist to Hip Ratio Risks increase with increasing ratios
very high risk >0.94 young men and 0.82 young women very high risk >1.03 older (60-69 years) men and 0.90 for older women

Measurements Made with a tape measure
Waist - at the narrowest part of the waist between the umbilicus and xiphoid process Hips - biggest part of the gluteals

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

BMI 20-25 kg/m2 - desirable 25-29.9 kg/m2 - overweight
> obesity