Lecture 2 - 8/20/2010 Objectives PSIO 445/545 Human Body...

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Unformatted text preview: 8/20/2010 Objectives PSIO 445/545 Human Body Composition Field Methods: Anthropometry, Somatograms, Body Somatograms, Mass Index, Bioelectric Impedance, Session Session #2 Thursday August 26th, 2010 Introduce Introduce the components of physique Definition Definition of anthropometry Understand Understand how anthropometry is used to assess body composition Introduce Introduce some anthropometric techniques used to assess body composition Overview Overview of underlying assumptions of anthropometry, skinfolds and BIA Overview Overview of sources of error Overview Overview of how equations are developed/chosen Overview Overview of method accuracy and SEE Physique Size Structure Size Mass Volume Volume Lengths Lengths Stature Stature CircumCircumferences Skinfolds Skinfolds Structure Somatotype Somatotype Somatogram Somatogram (qualitative; quantitative) Distribution Distribution (ratios) Relative to height Composition % fat fat % FFM FFM % water water % protein protein % mineral mineral Relative to weight Composition Perception of body physique Somatotype http://www.naturalmuscle.com.au/images/bodytypes.jpg 1 8/20/2010 Anthropometric Variables Relevant to Body Composition Anthropometry Anthropometry Anthropometry refers to the measurements of the size and proportion of the human body Lengths: Stature, Lengths: Stature, arm span, knee height Breadths: Breadths: Knee, ankle elbow wrist Circumferences: Circumferences: Waist, hip, arm, wrist Skinfold Skinfold Thicknesses Area: Area: Body surface and cross-sectional crossVolume: Volume: Body volume Weight: W eight: Body weight Assumptions Circumferences Circumferences are affected by fat mass, muscle mass, and skeletal size; therefore, these measures are related to fat mass and lean body mass Tissues Tissues are in a “standard” state (i.e. relaxed, normally hydrated) Anthropometry: most common measures Height/weight Height/weight or stature (e.g. BMI) Skinfolds Skinfolds (e.g. triceps, abdominal) - only subcutaneous fat Circumferences Circumferences (e.g. waist) - includes bone/fat/muscle Diameters Diameters (e.g. sagittal) sagittal) Ratios Ratios (e.g. Waist-Hip Ratio) Waist- Anthropometry and % body fat Can Can we estimate % fat from anthropometry? SKF % fat, FFM % fat, FFM % fat, FFM Skinfolds Circumference Skeletal diameters 2 8/20/2010 Estimation of Body Composition from Skinfolds: Assumptions Skinfolds: Skinfolds are a good measure of subcutaneous fat Total fat is well represented by subcutaneous fat Constant relationship between subcutaneous fat and other (intra-muscular, inter-muscular, visceral) fat deposits Constant fat pattern among individuals Constant fat-free mass composition and density There is a relationship between the sum of skinfolds and body density SKF SKF body density % fat Skinfold Skinfold = Double Layer of Skin + Subcutaneous Adipose Tissue Tools of the trade: Skinfold Calipers Skinfold Sites Lange or Harpendon preferred Sources of Error Biological Biological Difference Difference in fat patterning (“apples” vs. “pears”; appendicular vs truncal) Differences Differences in fat distribution (internal vs. subcutaneous) Differences Differences in composition and density of FFM Sources of Error Technical Technical (Measurement) Type Type of caliper Site Site location Technician Technician skill Valid Valid equation 3 8/20/2010 Choosing Appropriate Equation PopulationPopulation-specific versus generalized Validation Validation CrossCross-validation Prediction Prediction Body Mass Index - BMI Inches and pounds Kilograms and meters http://www.forthealthcare.com/media/images/obesity-table.gif BMI Issues Gender Gender Age Age Lean Lean Mass vs. Fat Mass Fat Fat Distribution/Patterning Bioelectric Impedance Analysis 4 8/20/2010 Bioelectrical Impedance Analysis Principles • Bioelectrical tissues act as conductors or insulators, and the flow of current through the body will follow the path of least resistance • Impedance is a function of resistance, where Z= R 2 + X c 2 Bioelectrical Impedance Analysis Principles Z= R 2 + Xc 2 pure opposition to current flow opposition to current flow caused by capacitance of the cell membrane Z = impedance (Ω ) R = resistance (Ω ) Xc = reactance (Ω ) BIA Assumptions The The human body is shaped like a perfect cylinder with a uniform length and crosscrosssectional area. BIA FiveFive-cylinder model L A Circuit Equiv. Model BIA Assumptions The The body is a perfect cylinder and, at a fixed signal frequency, the impedance (Z) to current flow is directly related to the length (L) of the conductor and inversely related to its cross-sectional area (A) mul crossThus, Impedance Thus, Impedance (Z) = ρ(L/A) 5 8/20/2010 Bioelectrical impedance Z = ρ (L/A) Z = impedance ρ = specific resistivity of body’s tissues (assumed constant) L = conductor length (body height) A = cross-sectional area cross- Volume (TBW, ECW, FFM) is directly related to L2 and inversely related to Z We know, Z = ρ (L/A) If we multiply each side by (L/L) (L/L)(Z) = ρ (L/A)(L/L) We get Z = ρ (L2/AxL) AxL) Since AxL = Volume Z = ρ (L2/V) Thus, Volume (V) = ρ (L2/Z) What else can we do with this? Since, V = ρ L2 Z BIA Prediction Equations TBW ECW FFM = b1 (HT2/R) + bo = b1 (HT2) + b2 (R) + bo % Fat = b1 (HT2/R) + b2 (WT) + bo Substitute, HT for L and R for Z Thus, where, V = ρ HT2 HT R HT2 = resistance index R Height in centimeters (cm) and resistance in ohms ( ) BIA tetrapolar method Four Four electrodes – hand, wrist, foot and ankle Excitation Excitation current, 500 µA to 800 µA at 50 KHz (single frequency) Source Source electrodes on hand and foot Voltage Voltage drop due to impedance detected by sensor electrodes on wrist and ankle Electrode Placement 6 8/20/2010 Proximal and distal electrode placement BIA prediction models Population– Population–specific for homogenous subgroups Separate Separate equations: age, race/ethnicity, gender, physical activity level (athletes), level of body fatness Generalized Generalized for heterogeneous populationspopulationsaccount for biological variability by including age, race, fatness, etc. as predictors BIA Sources of measurement error Instrumentation Instrumentation Subject Subject factors – eating, drinking, dehydration, exercising, temperature, subject position (fluid status-amount, statusdistribution) Technician Technician skill (electrode placement) Environmental Environmental factors Factors affecting BIA assessment of body comp Factor Type of Analyzer RJL vs. Valhalla Eating or drinking within 4 hrs Dehydration Aerobic Exercise Low Intensity Moderate-High Intensity Menstrual Cycle Follicular vs. Pre-Men Menses vs. Follicular Electrode Placement Electrode Configuration Ipsilateral vs. Contralateral Right side vs. Left side Room Temperature Effect on Resistance 16-18 13-17 40 NC 50-70 5-8 7 10 70 NC NC 35 Effect on FFM (kg) 1.0-1.3 1.5 5.0 NC 12.0 NC NC NC 11 NC NC 2.2 Deurenberg et al. (1988) Reference Graves et al. (1989) BIA Client Measurement Guidelines No eating or drinking within 4 hours of the test No exercise within 12 hours of the test Lukaski (1986) Urinate within 30 minutes of the test Deurenberg et al. (1988) Khaled et al. (1988); Lukaski (1986) Gleichauf and Rose (1989) Elsen et al (1987) Lukaski (1986) Lukaski et al (1985) Graves et al. (1989) Caton et al (1988) No alcohol consumption within 48 hours of the test No diuretic medications within 7 days of the test No testing of female clients who perceive they are retaining water during their menstrual cycle. 14°C vs. 35°C 7 8/20/2010 BIA Equation Finder (Heyward (Heyward and Stolarczyk, 1996, Applied Body Composition Assessment) BIA Equation Finder (Heyward (Heyward and Stolarczyk, 1996, Applied Body Composition Assessment) How to develop a BIA equation? Population Population (adequate sample) CriterionCriterion-method RegressionRegression-coefficient for resistance index versus other predictors Validation Validation results: R2, SEE CrossCross-validation results BIA versus skinfolds Does Does not require high degree of technician skill More More comfortable; does not intrude on privacy Useful Useful in obese individuals, with populationpopulation-specific equations Method Accuracy-How accurately can Accuracycomposition be measured? Rating Ideal Excellent Very Good Good Somewhat Good Fair Not Adequate Review Questions What W hat is physique? What W hat is a somatotype? somatotype? Are Are anthropometric measurements used to assess body composition? If so, which measurements are commonly used? What W hat body property do skinfolds estimate? What W hat are the issues with using BMI to estimate body composition? What W hat body component(s) is/are measured by BIA? SEE Method (%Fat) 1-2% 2.0% 2.5% 3.0% 3.5% 4.0% 5.0% IVNAA; MRI; CAT DXA; Tritium Dilution; Hydrometry Densitometry Densitometry; Potassium Skinfolds; Circumferences Skeletal Widths BMI 8 ...
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This note was uploaded on 01/30/2011 for the course PSIO 445 taught by Professor Staff during the Fall '08 term at University of Arizona- Tucson.

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