EXCI252Ch8AssessingBodyCompostionF2023Part1.pptx
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Chapter 8 Assessing Body Composition Part 1 EXCI 252 1 Body Fat Percentage Categories for Adults Aged 20 to 39 Years Age Sex Recommended % Body Fat VL Lean Ave Over fat Obese M 4-7 8-12 13-17 18-23 > 23 F 11-15 16-18 19-22 23-28 > 28 M 7-11 12-16 17-20 21-25 > 25 F 11-1...
Chapter 8 Assessing Body Composition Part 1 EXCI 252 1 Body Fat Percentage Categories for Adults Aged 20 to 39 Years Age Sex Recommended % Body Fat VL Lean Ave Over fat Obese M 4-7 8-12 13-17 18-23 > 23 F 11-15 16-18 19-22 23-28 > 28 M 7-11 12-16 17-20 21-25 > 25 F 11-16 17-19 VL = Very lean, Ave = Average. 20-23 24-30 > 30 20 - 29 30 - 39 EXCI 252 2 Body Composition Fat Mass (FM) All the fat in the body. Fats that can be extracted from the fat tissues & other tissues in the body. Also called Fat Weight. Estimated FM = % Body Fat x Total Body Weight. Fat-Free Mass (FFM) All fat-free tissues in the body, including water, muscle, bone, minerals, connective tissue, & internal organs. Also called Fat-Free Weight. Estimated FFM = Total Body Weight – FM Lean Body Mass (LBM) Contains the small percentage of essential fat stores. Represents an in vivo entity that remains relatively constant in its content of water, organic matter, & minerals throughout the adult’s life span. EXCI 252 3 Body Fat Essential Fat Nonessential Fat EXCI 252 4 Essential Fat ◆ includes lipids in the: Nerves Brain Heart Muscles Lungs Liver Kidneys Spleen Intestines Mammary glands Bone marrow Lipid-rich tissues of the CNS The larger percentage in women = fat deposits in breasts, uterus, & other sites specific to females = additional sex-specific essential fat. These fat deposits are necessary for normal physiologic functioning in men & women. EXCI 252 5 Nonessential Fat or storage fat is found primarily in fat cells (adipose tissue). Adipose tissue contains about: 83% pure fat, 15% water, & 2% protein. Location: Subcutaneous (below the skin) Visceral (around major organs) The amount of storage fat depends on: gender, age, heredity, metabolism, diet, & activity level. EXCI 252 6 Reference Man & Reference Woman Reference Standards Developed by Dr. Behnke Variable Reference Man Reference Woman 20-24 20-24 Age (yrs) Stature (cm) 174.0 163.8 Body Mass (kg) 70.0 56.7 LBM (kg) 61.7 88.1 % 48.2 85.0 % Muscle (kg) 31.3 44.7 % 20.4 36.0 % Bone (kg) 10.4 14.9 % 6.8 12.0 % Total Body Fat (kg) 10.5 15.0 % 15.3 27.0 % Storage Fat (kg) 8.4 12.0 % 8.5 15.0 % Essential Fat (kg) 2.1 3.0 % 6.8 12.0 % EXCI 252 7 Body Composition Models BC Assessment Method Component Model Largely 2 C (Some Multiple C equations) Skinfolds (SKFs) Hydrostatic Weighing (HW) 2C Air Displacement Plethysmography (ADP) 2C Near-Infrared Interactance (NIR) 2C Bioelectrical Impedance Analysis (BIA) 3C Dual Energy X-Ray Absorptiometry (DEXA) 3C Computed Tomography (CT) Multiple C Magnetic Resonance Imaging (MRI) Multiple C EXCI 252 8 Two-Component Model of Body Composition Fat Component Fat-Free Body (FFB) Component References: Brozek, Grande, Anderson, & Keys (1963), & Siri (1961). EXCI 252 9 5 Assumptions of the 2-Component Model of Body Composition 1. The density of fat is 0.901 g·cm-3. 2. The density of FFB is 1.100 g·cm-3. 3. The densities of fat & the FFB components (water, protein, mineral) are the same for all individuals. 4. The densities of the various tissues composing the FFB are constant within an individual, & their proportional contribution to the lean component remains constant. 5. The individual being measured differs from the reference body only in the amount of fat; the FFB of the reference body is assumed to be 73.8% water, 19.4% protein, & 6.8% mineral. EXCI 252 10 Brozek, Grande, Anderson, & Keys (1963) Dissected: 3 white male cadavers They measured the density of: Body Fat = 0.901 g·cm-3 (g·cc-1) Fat-Free Mass = 1.100 g·cm-3 (g·cc-1) EXCI 252 11 Two-Component Model Equations Estimation of % Body Fat Siri (1961) Equation: % Body Fat = [(4.95 / Db) – 4.50] x 100 Brozek, Grande, Anderson, & Keys (1963) Equation: % Body Fat = [(4.57 / Db) – 4.142] x 100 Db = total body density EXCI 252 12 2-Component Model of Body Composition According to research, FFB Density varies with: age, growth, sexual maturation, gender, ethnicity, level of body fatness, physical activity level, and a number of diseases. FFB density: depends mainly on the relative proportions of water & mineral that compose the FFB component. EXCI 252 13 Classic 2-Component Model Group Average FFB Density (g·cc-1) Estimation of Body Fat % Using 2-C Model Equations Explanation Black Men & Women ~ 1.106 Underestimated Higher mineral content (~ 7.3% FFB) and/or higher relative body protein. Pro Football Players > 1.100 Underestimated Higher mineral content and higher relative body protein. White Children 1.086 Overestimated Lower mineral content (5.2% FFB). Higher body water values (76.6% FFB). Elderly White Men & Women 1.098 Overestimated Lower body mineral content (6.2% FFB). EXCI 252 14 Multicomponent Models of Body Composition Eliminate much of guesswork in 2-C model assumptions. Based on measurements of total body water & bone mineral values. Useful for developing population-specific formulas. EXCI 252 15 Population-Specific Formulas For Converting Db to %BF Ethnicity African American, American Indian, Japanese, Singaporean, Hispanic, & White. Age Children, adolescents, young adults, & elderly individuals. Athletes Resistance-trained, endurance trained, & all sports. Clinical Populations Anorexia nervosa, obesity, & spinal cord injury. (Refer to Table 8.2.) EXCI 252 16 Population-Specific 2-C Formulas For Converting Db to %BF Table 8.2 EXCI 252 17 Reference Methods for Assessing Body Composition Densitometric Methods estimate total body density (Db) Db = Body Mass/Body Volume = BM/BV Hydrostatic Weighing (HW) & Air Displacement Plethysmography (ADP) are used to measure body volume Dual-Energy X-Ray Absorptiometry EXCI 252 18 Hydrostatic Weighing is valid & reliable. is a widely used laboratory method for assessing total Db. provides an estimate of BV from the volume of water displaced by the body’s volume. is based on Archimedes’ principle of water displacement which states that “a body immersed in water is buoyed up with a force equal to the weight of the water displaced.” weight loss under water is directly proportional to the volume of water displaced by the body’s volume. EXCI 252 19 Hydrostatic Weighing Db = BM / BV Db = Wa / [((Wa – Ww) / Dw) – (RV + GV)] Wa = body weight (mass) in air (out of water) Ww = net body weight (mass) in water = net UWW Dw = density of water at a given temperature RV = residual volume in the lungs GV = volume of air in the gastrointestinal tract EXCI 252 20 Hydrostatic Weighing Weight of Water Displaced = Wa – Ww Ww (Net UWW) = Gross UWW – Tare Weight Tare Weight = weight of chair or platform & supporting equipment Uncorrected Body Volume Volume of water displaced with air in the body = (Wa – Ww) / Dw Corrected Body Volume Volume of water displaced without air in the body = [((Wa – Ww) / Dw) – (RV + GV)] GV is assumed to = 100 mL (0.1 L), unless it is measured EXCI 252 21 Hydrostatic Weighing Measurements of the following variables are needed to calculate Db: Dry Land Weight ± 50 g Underwater Weight ± 100 g Water Density Depends on water temperature Residual Lung Volume ± 100 mL Gastrointestinal Tract Volume Assumed value = 100 mL EXCI 252 22 Hydrostatic Weighing Underwater Weight HW using a chair attached to an autopsy or a spring scale. HW using a platform attached to load cells (transducer system). EXCI 252 23 Hydrostatic Weighing Water Density Water Temp (oC) Density H2 O Water Temp (oC) Density H2 O 23 0.9975412 31 0.9953450 24 0.9972994 32 0.9950302 25 0.9970480 33 0.994734 26 0.9967870 34 0.9947071 27 0.9965166 35 0.9940359 28 0.9962371 36 0.9936883 29 0.9959486 37 0.9933328 30 0.9956511 Density = g·cc-1 or g·mL-1. Normally, the water temperature should range between 34 & 36 oC. EXCI 252 24 Hydrostatic Weighing Residual Lung Volume Residual Lung Volume (RV) = the volume of air remaining in the lungs after a maximal expiration. is the volume least affected by hydrostatic pressure. can be measured before, during, or after underwater weighing. of 1.0 to 2.4 L is the typical range for adults. EXCI 252 25 Hydrostatic Weighing Residual Lung Volume Measurement Methods of RV Closed-Circuit Approach Oxygen Dilution Nitrogen Dilution Helium Dilution Open-Circuit Approach Nitrogen Washout EXCI 252 26 Hydrostatic Weighing Residual Lung Volume Formulas Used To Estimate Residual Volume in Liters Gender Equation Male RV = (0.017 x Age) + (0.027 x Ht) – 3.447 Female RV = (0.009 x Age) + (0.032 x Ht) – 3.90 Age in years & Ht (height) in cm (Goldman & Becklake, 1959). EXCI 252 27 Sources of Error in Hydrostatic Weighing Pretesting Guidelines Eating Strenuous exercise Gas-producing foods or beverages Equipment Calibration Before Testing BW scale, UWW scales or load cells Gas analyzers for RV Equipment Used UWW scale or load cell system Measurements of BW, UWW, & RV Precision Is RV estimated or measured? Are RV and UWW measured simultaneously? Client Factors Maximal exhalation Motionless under water Calculated Db Value 5 decimal places Conversion Formula Use the appropriate population-specific conversion formula EXCI 252 28 Modification of HW Procedures UWW Client at Functional Residual Capacity (FRC) UWW Client at Total Lung Capacity (TLC) UWW Client at TLC With the Head Above Water Level EXCI 252 29 UWW Client at Functional Residual Capacity is used when a client is unable to expel all of the air from the lungs. Db is measured at the FRC. FRC = ERV + RV. FRC = volume of air remaining in the lungs at the end of a normal expiration. ERV = expiratory reserve volume = maximal volume of air that can be expired from the lungs after a normal expiration. Must still measure RV. Db = Wa / [((Wa – Ww) / Dw) – (FRC + GV)] EXCI 252 30 UWW Client at Total Lung Capacity is used when a client is unable to expel all of the air from the lungs. Db is measured at TLC. TLC = VC + RV. TLC = volume of air in the lungs after a maximal inspiration. VC = maximal volume of air that can be expired from the lungs after a maximal inspiration. Must still measure RV. Db = Wa / [((Wa – Ww) / Dw) – (TLC + GV)] EXCI 252 31 UWW Client at TLC With the Head Above Water Level is used when a client: is fearful of being submerged, dislikes facial contact with the water, or is unable to bend forward to assume the proper body position. Db is measured at TLC with head not submerged (TLCNS). Gender-specific prediction equations estimating Db at RV from the measurement of Db at TLCNS exist. Prediction equations for Db at RV using Db determined at TLC with head not submerged (TLCNS) Prediction Equation r SEE (g·cc-1) Male Db at RV = 0.5829 (Db at TLCNS) + 0.4059 0.88 0.0067 Female Db at RV = 0.4745 (Db at TLCNS) + 0.5173 0.85 0.0061 Gender EXCI 252 32 Lung Capacities and Volumes EXCI 252 33 The Effect of Measurement Error on the Determination of BV, Db, & % BF from HW Overestimate Body Volume Db % BF Dry Land Weight Overestimated Underestimated Overestimated Underwater Weight Underestimated Overestimated Underestimated Water Temperature Overestimated Underestimated Overestimated Residual Volume Underestimated Overestimated Underestimated EXCI 252 34 Disadvantages of UWW Procedure is time-consuming Equipment is fairly expensive Requires adequate space & plumbing & high maintenance Accurate test results are highly dependent on the client’s skill, cooperation, & motivation Some clients may not be able to perform the procedure. Complete water submersion at full exhalation Requires measurement of residual lung volume: Additional equipment is needed EXCI 252 35 Calculate % Body Fat Body Density = [Body Mass / Body Volume] Body Volume = [((BM in kg – Net UWW in kg) / (Density of H2O)) – (RV in L + 0.100 L)] Relative Fat (%) = (495 / Body Density) – 450 (Siri’s Equation) Fat Mass = Body Mass x Relative Fat (%) Fat-Free Mass = Body Mass – Fat Mass Target Body Weight = (Fat-Free Mass) / (100% – Goal Fat %) EXCI 252 36 Sample 1 Calculation of % Body Fat Sex: Male Age: 18 years Height: 70 inches Weight: 180 lb (81.8 kg) Net Underwater Weight: 3.8 kg Estimated RV: 1660 mL Estimated RV + 100 ml (trapped GV) = 1760 mL = 1.760 L Density of water at 30 oC: = 0.9956511 1 kg = 2.2 lb EXCI 252 37 Sample 1 Calculation of % Body Fat Body Volume = [((81.8 kg – 3.8 kg) / 0.9956511) – (1.760 L)] = [(78 kg / 0.9956511) – (1.760 L)] = (78.340695 L – 1.760 L) = 76.58 L Body Density = (81.8 kg / 76.58 L) = 1.06816 (5 decimal places) Relative Fat (%) Fat Mass = (495 / 1.06816) – (450) = (463.41 – 450) = 13.4% = (81.8 kg x 13.4%) = (81.8 x 0.134) = 10.96 kg = (10.96 kg x 2.2 lb/kg) = 24.1 lb Fat-Free Mass = (81.8 kg – 10.96 kg) = 70.84 kg = (70.84 kg x 2.2 lb/kg) = 155.9 lb Goal Fat % = 10% Target Body Wt = ((70.84 kg) / (100% – 10%)) = (70.84 / 0.90) = 78.71 kg = (78.71 kg x 2.2 lb/kg) = 173.2 lb How much body fat does this person have to lose? Total Body Wt – Target Body Wt = 180.0 lb – 173.2 lb = 6.8 lb EXCI 252 38 Sample 2 Calculation of % Body Fat Calculate the % BF for the following person: Body Weight = 70.15 kg Net Underwater Weight = 3.36 kg Residual Volume = 1100 mL Gastrointestinal Tract Volume = 100 mL Water Density = 0.9956511 at 30 oC EXCI 252 39 Air Displacement Plethysmography The Bod Pod is used to measure body volume & density. uses air displacement to estimate body volume. EXCI 252 40 Air Displacement Plethysmography Boyle’s Law At a constant temperature (isothermal condition) volume (V) and pressure (P) are inversely related P1 / P2 = V2 / V1 P1 & V1 = when the Bod Pod chamber is empty P2 & V2 = when the client is in the Bod Pod chamber Body Volume = V1 – V2 = volume of air in the empty chamber – volume of air remaining in the chamber when the client is inside = volume of air displaced when a client sits in the chamber Body Density = Body Mass / Body Volume EXCI 252 41 Bod Pod Testing Minimal Clothing requires a swimsuit Swim Cap to compress the hair corrects for the isothermal effects of hair Estimation of Body Surface Area (BSA) from height & weight measurements corrects for the isothermal effects at the body’s surface Measurement or Estimation of Thoracic Gas Volume (TGV) TGV = volume of air in the lungs (FRC) at midexhalation body volume must be corrected for TGV accounts for the isothermal conditions in the lung EXCI 252 42 Factors That Affect Accurate Bod Pod Test Results Sources of Isothermal Air Excess body hair Excess facial hair Scalp hair More clothing Body (skin) surface area Thoracic gas volume EXCI 252 43 Sources of Error in ADP Pretesting Guidelines Same as HW Completely void bladder & bowels Swimsuit & Swim Cap Eliminate the effects of isothermal air due to body hair Body Surface Area Height (nearest cm) Body weight (nearest 5 g) EXCI 252 44 Sources of Error in ADP Deviations in Normal Tidal Volume Breathing Can affect body volume & % BF estimations if a Bod Pod does not have a software upgrade that guides clients through the TV breathing cycles during TGV assessment. Research by Tegenkamp & Colleagues (2011) Body Volume Measurement Procedure • Deeper breathing: 2.1% lower BF • Shallower breathing: 2.2% higher BF TGV Measurement Procedure • Deeper breathing: 3.7% higher BF • Shallower breathing: 3.4% lower BF EXCI 252 45 Sources of Error in ADP Performance of Two-Point Calibration 1. Baseline calibration (empty chamber) 2. 50 L calibration cylinder Thoracic Gas Volume TGV measurement is better than a predicted TGV Client Factors Must remain still during the 20 s test EXCI 252 46 Advantages and Disadvantages of ADP Advantages of ADP Quick to administer: 5 minutes Requires minimal client compliance Requires minimal technician skill Instructions to clients are minimal The Bod Pod is mobile Can accommodate special populations Disadvantages of ADP Equipment is expensive Equipment is generally accessible only in research facilities Requires special clothing EXCI 252 47 Dual-Energy X-Ray Absorptiometry DEXA is increasingly used as a reference method for BC research. EXCI 252 48 Dual-Energy X-Ray Absorptiometry Bone Mass Yields estimates of bone mineral, fat, lean soft-tissue & visceral adipose tissue (VAT) mass at the whole-body level & regional (trunk & appendicular) level. Soft Tissue EXCI 252 49 DEXA The subject lies supine (lying face upward) on a table so that the source & detector probes pass across the body slowly. 2 distinct low-energy x-ray beams penetrate bone & soft tissue areas to a depth of about 30 cm. Computer software reconstructs the attenuated xray beams to produce an image of the underlying tissues & quantify bone mineral content, total FM, & FFM. Attenuation is defined as the loss of energy of a beam of radiant energy due to absorption. weakening of X-rays through fat, lean tissue, & bone. EXCI 252 50 Advantages and Disadvantages of DEXA Advantages of DEXA Safe Rapidly administered Whole-body scan = 3 to 20 min Depends on DEXA model, type of scan beam, age of DEXA machine, & client’s stature. Requires minimal client cooperation Requires minimal technical skill Accounts for individual variability in bone mineral content most important Offers a less expensive & safer option to assess VAT than the gold standard methods, computed tomography (CT) & magnetic resonance imaging (MRI). Disadvantages of DEXA Equipment is expensive Equipment is generally accessible in clinical or research settings EXCI 252 51 Factors Affecting the Accuracy of DEXA Results Fasting Prior to a DEXA Scan Increases the accuracy of the body composition assessment Sagittal Abdominal Diameter Use a skeletal anthropometer to accurately determine body thickness Calibration of DEXA Scanner Calibrate DEXA scanner with calibration marker provided by the manufacturer Variability Among DEXA Technologies is a major source of error Differ in their generation of the high- and low-energy beams: filter or switching voltage Imaging geometry: pencil beam, fan beam, or narrow fan beam X-ray detectors Calibration methodology Algorithms Software versions EXCI 252 52
