Body Composition Body Composition 2 component model Fat tissue Fat free tissue Body Composition Why the interest? Excess body fat • Hypertension • Type 2 diabetes • Hyperlipidemia • Certain cancers • Poor performance/function • Poor self-image Incident of overweight is ↑ng Want to “look good” Body Composition Terminology Depot or storage fat – fat stored in adipose cells as nutritional reserve Essential fats – fats necessary for normal physiologic function Body Composition Terminology Lean body mass (wt) – body mass minus depot fat Fat free mass (wt) – body mass minus all fat (depot & essential) Body Composition Relative %age of body weight that is fat & fat-free tissue Lab & field tests vary in complexity, expense Anthropometry Measurement of the human body Anthropometry Ht/wt Circumference/girths Skinfolds Hydrostatic weighing Bioelectrical impedance DXA TOBEC X-ray Body Composition - %Fat Norms Classification Women Men Essential Fat 11.0 - 14.0 3.0 - 5.0 Athletes 12.0 – 22.0 5.0 – 13.0 Fitness 16.0 - 25.0 12.0 – 18.0 Potential Risk 26.0 – 31.0 19.0 – 24.0 ≥ 32.0 ≥ 25.0 Obese Body Composition - Tests • Densitometry – Two component model • Fat & fat free mass – Ratio of body mass to body volume (DB=BW/BV) – Body mass determined form body weight – Body volume from under water weighing or plethysmography Densitometry • Hydrostatic (under water) weighing –Criterion, gold standard Densitometry • Hydrostatic (under water) weighing – Archimedes’ principle – when a body is immersed in water, it is buoyed by a counterforce equal to the weight of the water displaced – The loss of weight in water, corrected for density of the water, allows calculation of body volume Densitometry • • • • • RV Density of H2O Trapped gas in GI tract (100 ml) Body weight (dry) Body weight (wet) Body Composition Densitometry Body density = weight in air (weight in air – weight in water) – Residual Density of the water volume Body Composition Densitometry Body density = bone & muscle more dense than water, fat tissue less dense Body Composition Densitometry Plethysmography • air displacement – Δs in pressure in a closed chamber Bodpod Body Composition Densitometry %fat = 457 Body Density - 414.2 %fat = 495 Body Density - 450 Body Composition – Anthropometric Methods • • • • Height Weight Circumferences Skinfolds Body Composition – Anthropometric Methods • Reliability & validity – Skill of the measurer – Type of caliper or tape measure – Subject factors related to skinfold compressibility, edema, & variability in fat pattern & distribution – Prediction equation used to estimate fatness Body Composition – Anthropometric Methods • Body Mass Index (BMI) – – – – – – Assess weight relative to height [body weight (kg)/height (m2)] BMI > 25 – increased health risk 25.0 to 29.9 = Overweight > 30 = Obese See Table 4-1 pg.58 & Table 4-2 pg.59 Body Composition – Anthropometric Methods • Waist-to-hip circumference – Body fat distribution – More fat on trunk (abdominal fat) = greater risk of HTN, type 2 diabetes, hyperlipidemia, CAD, premature death – Health risk is high • • • • W/H ratio > 0.94 in young men W/H ratio > 0.82 in young women W/H ratio > 1.03 in men 60-69 yrs W/H ratio > 0.90 in women 60-69 yrs See Box 4-1 & Table 4-3 pgs.60-61 ACSM GET&P Classification of Disease Risk Based on Body mass Index (BMI) and Waist Circumference (Table4-1) Disease Risk Relative to normal Weight and Waist Circumference BMI, kg/m2 Underweight <18.5 Men, 102cm; Women,88cm … Normal 18.5-24.9 … … Overweight 25.0-29.9 Increased High I 30.0-34.9 High Very high II 35.0-39.9 Very high Very high III 40 Extremely high Extremely high Men >102cm; Women, >88cm … Obesity class Body Composition – Anthropometric Methods • Skinfolds – Amount of subcutaneous fat is proportional to total body fat Box 4-2. Standardized Description of Skinfold Sites & Procedures Continued • Procedures – All measurements on the right side of the body – Caliper should be placed 1 cm away from the thumb & finger, perpendicular to the skinfold, & halfway b/n the crest & the base of the fold Box 4-2. Standardized Description of Skinfold Sites and Procedures Continued – Pinch should be maintained while reading the caliper – Wait 1 to 2 s (& not longer) before reading caliper – Take duplicate measures at each site & retest if duplicate measurements are not w/n 1 to 2 mm – Rotate through measurement sites or allow time for skin to regain normal texture & thickness Box 4-2. Standardized Description of Skinfold Sites & Procedures • Skinfold Site – Abdominal – Triceps – Biceps Vertical fold; 2cm to the right side of the umbilicus Vertical fold; on the posterior midline of the upper arm, halfway between the acromion & the olecranon processes, w/ the arm held freely to the side of the body Vertical fold; on the anterior aspect of the arm over the belly of the biceps muscle, 1 cm above the level used to mark the triceps site Box 4-2. Standardized Description of Skinfold Sites & Procedures Continued • Skinfold Site Continued – Chest/Pectoral Diagonal fold; one-half the distance between the anterior axillary line & the nipple (men) or one-third the distance b/n the anterior axillary line & the nipple (women) – Medial Calf Vertical fold; at the maximum circumference of the calf on the midline of its medial border Box 4-2. Standardized Description of Skinfold Sites & Procedures Continued • Skinfold Site Continued – Midaxillary Vertical fold; on the midaxillary line at the level of the xiphoid process of the sternum (An alternate method is a horizontal fold taken at the level of the xiphoid/sternal in the midaxillary line – Subscapular Diagonal fold (at a 45 angle); 1 to 2 cm below the inferior angle of the scapula Box 4-2. Standardized Description of Skinfold Sites & Procedures Continued • Suprailiac Diagonal fold; in line w/ the natural angle of the iliac crest taken in the anterior axillary line immediately superior to the iliac crest • Thigh Vertical fold; on the anterior midline of the thigh, midway b/ the proximal border of the patella & the inguinal crease (hip) Table 4-5. Body Composition (%Body Fat) For Men* Age Percentile 20-29 30-39 40-49 90 7.1 11.3 13.6 80 9.4 13.9 16.3 70 11.8 15.9 18.1 60 14.1 17.5 19.6 50 15.9 19.0 21.1 40 17.4 20.5 22.5 30 19.5 22.3 24.1 20 22.4 24.2 26.1 10 25.9 27.3 28.9 50-59 15.3 17.9 19.8 21.3 22.7 24.1 25.7 27.5 30.3 60+ 15.3 18.4 20.3 22.0 23.5 25.0 26.7 28.5 31.2 Table 4-6. Body Composition (%Body Fat) For Women* Age Percentile 20-29 30-39 40-49 90 14.5 15.5 18.5 80 17.1 18.0 21.3 70 19.0 20.0 23.5 60 20.6 21.6 24.9 50 22.1 23.1 26.4 40 23.7 24.9 28.1 30 25.4 27.0 30.1 20 27.7 29.3 32.1 10 32.1 32.8 35.0 50-59 21.6 25.0 21.3 28.5 30.1 31.6 33.5 35.6 37.9 60+ 21.1 25.1 25.0 29.3 30.9 32.5 34.3 36.6 39.3 Body Composition – Other Techniques • Bioelectrical Impedance Analysis (BIA) – Volume of FFM is proportional to the electrical conductivity of the body – Small electrical current is passed through body – Measures resistance to current • Fat is poor conductor – 14 to 22% water • Lean tissue is good conductor - >90% water – Assumes normal hydration Body Composition – Other Techniques • Bioelectrical Impedance Analysis (BIA) – – – – Does not require a high degree of technical skill More comfortable Requires minimal cooperation Intrudes less on privacy Body Composition – Other Techniques • Dual Energy X-ray Absorptiometry (DEXA) – Assess total bone mineral, bone, fat, & lean tissues – Uses three component model (fat, solids, water) • Near-infrared interactance (NIR) – Light absorption & reflection – Chemical composition of the body – Accuracy 4 to 11% Dual X-Ray Absorptiometry Prediction Equations • Population specific – Derived on homogeneous population • General equations – Diverse, heterogeneous samples that account for differences in age, sex, race, ethnicity, etc. Prediction Equations • Equation Selection – To whom is the equation applicable – Was equation developed on an appropriate reference model? – Was a representative sample studied? – How were predictor variables measured? – Was the equation cross-validated? – Does equation give accurate estimates? (2.5 to 3.5% - %fat) (2.5 to 3.5 kg – FFM)