Evaluation of Body Composition

1. Evaluation of Body Composition Chapter 14

2. Height – Weight Tables Developed in 1940’s by INSURANCE companies. Based solely on mortality statistics. Fatter people = increased risk of death Do not take into account body composition!!!

3. Body Mass Index BMI = Weight (kg) / Height (m) 2 Desirable Men: 21.9 – 22.4 Women: 21.3 – 22.1 Over weight: 25 - 30 Obese: >30

4. Body Mass Index BMI’s above 27 associated with ? incidence of hypertension, diabetes, & CHD. Still used frequently by doctors and researchers. Does not take body composition into account either!

5. Height: 5’10” = 1.77 m Weight: 221 lbs = 100.45 kg BMI = 32.09 THIS GUY IS OBESE !!!! Body Mass Index

6. Structural Components Human body made up of: Water Protein (muscle) Fat Bone

7. Reference Man / Woman Developed by Albert Behnke, MD A theoretical model based on an “average” person. Divides body into: Lean Body Mass Protein and Bone Fat Essential Non-essential or storage

8. Reference Man

9. Reference Woman

10. Essential fat Fat stored in: Bone marrow, heart, liver, lungs, spleen, kidneys, intestines, muscles, and CNS. REQUIRED for NORMAL physiological function. Women carry additional “gender specific” essential fat in mammary glands and in pelvic region, surrounding reproductive organs. (EF 3X’s greater in females)

11. Non-Essential / Storage Fat Fat accumulated in adipose tissue Serves as nutritional reserve Two compartments Visceral Subcutaneous

12. Lean Body Mass LBM = Body mass – storage fat Includes essential fat / Fat free mass does not include EF Male : 3% of LBM is essential fat = lower limit of leanness for normal function. Female : 12-14% of LBM is essential fat = lower limit of leanness for normal female function.

13. Too Thin? Men: Less than 4% BF Reduced exercise tolerance (especially LSD) Increased dissipation of heat, Less work during weight bearing exercise Women : Less than 17% BF Oligomenorrhea – irregular menstruation Amenorrhea – Cessation of menstrual cycle Bone mineral loss Decreased risk of cancer ? *

14. Assessing Body Composition Direct Messy / Requires dissection & chemical analysis Hard to recruit subjects Indirect Estimating body composition Hydrostatic weighing Skinfold measurements Girth measurements

15. Hydrostatic Weighing Based on Archimedes principle An object submerged in water has a counter force acting upward on it equal to the amount of water it displaces (buoyancy). Able to determine VOLUME

17. Hydrostatic Weighing By determining weight lost under water, we can compute volume. IE : 50 kg person weighs 2.5 kg under water 47.5 kg water displaced (density of 1 kg/L) = 47.5 liters of water displaced We know mass and volume; we can calculate density! Density = mass / volume Density = 50 kg / 47.5 L = 1.0526

18. Hydrostatic Weighing We know that fat and lean body tissue have relatively stable densities Fat = 0.9 g/cc Fat Free Tissue = 1.1 g/cc We can then calculate percent BF % BF = (495 / Body Density) – 450 +/- 2.5% error BF% = (495 / 1.0526) – 450 = 20.26%

19. Hydrostatic Weighing Draw Backs Constant used for density of fat and LBM Racial differences Young vs. old Active people – LBM = denser Facilities Requires exhaling ALL lung volume under water and estimation / measurement of RV

20. Skinfold Measurements Based on the rational that subcutaneous fat represents a certain % of total body fat. Skinfold thickness (3 – 7 sites) measured using specialized calipers that exert exactly 10 g/mm2 pressure. Sum of thickness readings can be placed into formulas to estimate BF % +/- 3.7% error!

21. Skinfold Measurements Drawbacks Not extremely accurate Large inter-tester error rate Variations in subjects (SC fat distribution) Positives Inexpensive equipment More accurate than other alternatives Easy test to perform

22. Girth Measurements Circumferences taken at different sights and a prediction equation is used to estimate body fat %. Book claims 4% error, depends on individual tested ! Waist to Hip ratio appears to be useful ! Drawbacks Does not take into account composition of girth (IE muscular individuals often over est.) Relatively large error

23. Bioelectric Impedance Increasingly popular technique that does not work!!! Measures body’s resistance to electricity Muscle less resistant (H2O and electrolytes) Fat is an insulator Estimates composition / density based on impedance of electrical current.

24. Bioelectric Impedance Drawbacks Hydration levels change and greatly effect outcomes (less water = higher BF) Exercise Fluid intake Female menstrual cycle Skin temperature Warm skin conducts electricity better (? BF)

25. Non Invasive Scanning Techniques CT Scan Cross sectional radiographic images of various parts of the body. Most often used to determine changes in subcutaneous fat in a limb. (research) MRI (magnetic resonance imaging) Electromagnetic radiation in strong magnetic field excites H+ ions in water and lipid molecules. Gives off measurable signal – image. Provides cross sectional images. Used most in research.

26. Non Invasive Scanning Techniques DEXA scan (dual-energy X-ray absorptiometry) Measures absorption of two different x-rays as they pass through body. Able to scan entire body in about 12 minutes. Able to quantify bone mineral content, fat free body mass, and total fat mass. Dual-photon Absorptiometry

27. Desirable Body Fat % Most Americans are still overweight!!! CDC Statistics: 1990’s 27% of women & and 24% of men are “significantly overweight” Unchanged from 1960’s Increased awareness of the health implications of being “over fat” is necessary. Linked to CHD, hypertension, cancer, diabetes, and stroke!

28. Desirable Body Fat % Men: <15% (18% for older men) Women: 12 - 25% (12 – 30% for older women) Body fat tends to increase as we age Less activity / same caloric intake Decreased metabolism Decrease in metabolically active muscle tissue Aging process (Hormonal changes, etc)

29. Calculations Calculating LBM (FFBM) & FM 100 kg (220 lb. Male w/ BF = 18%) Fat Mass = Body Mass X Percent Fat FM = 100 kg X .18 FM = 18 kg (39.6 lbs.) FFBM = Body mass – Fat Mass FFBM = 100 kg – 18 kg FFBM = 82 kg (180.4 lbs.)

30. Calculations Calculating desired body mass Body MassDesired = LBM / (1.0 – BF%Desired) Desirable Fat Loss Fat loss = Body MassPresent - Body MassDesired Remember: Often times LBM increases with exercise….Resulting in need to recalculate Body MassDesired or “Target Weight”