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Body Composition Assessment A description of assessment methods.

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

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

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

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Why measure body comp? n Health Implications –there is an ideal % fat for health reasons (prevent onset of diabetes, CHD, BP, etc…) n Make BW recommendations –can use % fat values to determine an ideal BW –how much fat to lose versus how much muscle to gain

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Why measure body comp? n 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

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Height - Weight Tables n 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.

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For example: n Body Builder: –5’5” –200 pounds –overweight according to height/weight tables –4% body fat –ALL MUSCLE!!!

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Fat Mass vs. Fat-free Mass n Two Component Model n 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.

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Assumptions of Two-Component Models n 1. The density of fat is 0.900 g/ml n 2. The density of FFM is 1.100 g/ml n 3. The densities of fat and FFM are the same for all individuals

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Assumptions n 4. The densities of the various components of FFM are constant within an individual n 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

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

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MODELS OF BODY COMPOSITION

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Essential Fat n All fat is not bad!! n We need fat for padding of organs, insulation, energy source n There is a minimum amount that we need to function daily = essential fat n Gender specific –males ~ 3% –females ~ 7%

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Essential Fat n 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

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Other Models n 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)

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Methods n 1. Under Water Weighing (Hydrodensitometry) n 2. Bioelectrical Impedance (BIA) n 3. Dual-Energy X-ray Absorptiometry (DEXA) n 4. Near-Infrared Interactance (NIR)

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Methods n Anthropometric Measures (anthro=body; metric=measures body measurements) n 5. Skinfolds n 6. Circumference (WHR) n 7. Diameters (body typing) n 8. Height (BMI) n 9. Others…..??

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Hydrodensitometry n Used to be considered the most accurate (up for debate now that DEXA is used) n +2.5% if done with experienced subjects n Considered a lab technique (can’t carry your tank with you out into the field) n Two-component Model

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UWW n Fat Component - Fat (adipose)+Neural+Essential Fat –density of 0.9 g/ml n Fat-Free Component - muscle+bones+ tendons+organs –density of 1.10 g/ml

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UWW n Water Density ~ 1.0 g/ml (temperature of the water affects the density) n Thus, if more fat will float (fat is less dense than water) n If more muscle will sink (muscle is more dense than water)

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

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UWW n Body Density = BW÷((BW-UWW)/H 2 0 Density) - RV-0.1

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

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

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Procedures n 1. Wear light clothing (swimsuit) n 2. Use bathroom prior to weighing n 3. Calibrate scale n 4. Weight the chair or seat and equipment n 5. Measure water temp n 6. Remove all air from clothing

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Procedures n 7. Sit in seat n 8. Submerge n 9. Blow all air out of lungs and remain still n 10. 3-10 trials; average of the highest three n 11. Subtract weight of apparatus from average UWW

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UNDERWATER WEIGHING TECHNIQUE

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

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Determining RV n Prediction equations based on height and/or Vital Capacity –Male = 0.24 x VC –Female = 0.28 x VC –Male = 0.019(Ht cm)+0.0115(age)-2.24 –Female = 0.023(Ht cm)+0.021(age)-2.978 n Nitrogen Analysis (rebreathing apparatus)

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Equations n 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. n Thus, we have age/gender/race/fat specific equations - Table 4-1 Guidelines

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Equations n % fat = 4.57÷BD - 4.142 * 100 n ACSM guidelines: –%fat = 457÷BD - 414.2

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Advantages n Accurate if done correctly n Many equations that are specific to each group

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

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

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BIA n Based on the premise that fat-free tissue is a better conductor of an electrical current (contains water and electrolytes) than fat tissue n The resistance to current flow is inversely related to FFM

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

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

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BIA n Abstain from eating or drinking for 4 hours prior n No exercise 12 hours prior n No alcohol 48 hours prior n No diuretics (caffeine) prior to assessment

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Equations n Each machine has its own equation (developed by the manufacturer and is proprietary) n %fat = 4.57 ÷ (1.1411 - ((BW * Resistance) ÷ Ht 2 )) - 4.142 * 100 –ht = length of the conductor

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

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

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

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Disadvantage n The accuracy has been questioned: –Skinfolds2.4 % error –BIA5% error –Visual3.1% error n Race cannot be entered into the machine n Children distribute water differently than adults

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

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

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Disadvantage n Costly n Limited Access

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NIR n Based on the premise that the degree of infrared light absorption is related to the composition of the substance through which light passes n Fat and Fat-Free Mass absorb and reflect light differently

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NIR n Emit infrared light at wavelengths of 940-950 nm into a body part (ie., biceps) and measures the intensity of the re-emitted light n More specific equations/machines are necessary

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Advantages n Non-invasive n Safe n Easy to administer n Field technique

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Disadvantages n Cost? Is it worth it? n Few Age/Gender Specific Equations n Accurate? –Futrex 50003.1-4.2% –Futrex 5000A6.3% –Futrex 10004.8-6.3% –Sum 32.4-3.6 –BIA5.0-7.1%

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Skinfolds n Measurement of subcutaneous adipose tissue at specific anatomical sites n BD or %fat is obtained with the use of equations (either population specific or generalized)

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SF Procedures n Take all measurements on the right side of the body n Identify and mark site n Grasp skin and fat between thumb and index finger 1cm above marked site n Continue grasping at the site while taking the measurement

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

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

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Sites n Chest n Subscapular n Midaxillary n Suprailiac n Abdominal n Triceps n Biceps n Thigh n Calf

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Equations n 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

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Waist to Hip Ratio n Indication of the pattern of body fat distribution n Indicator of the health risks of obesity –excess trunk fat - increased risk of hypertension, type 2 diabetes, high cholesterol, CAD, premature death

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Waist to Hip Ratio n 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

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

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Body Mass Index (BMI) n Ratio of a person’s weight (kg) to the height squared (m 2 ) n Used to categorize people with respect to their degree of obesity n Not used to determine % fat

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BMI n 20-25 kg/m2 - desirable n 25-29.9 kg/m2 - overweight n >30.0 - obesity

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