Body Composition

1. Body Composition Exercise Physiology McArdle, Katch, & Katch – Ch. 16

2. Gross Composition of Human Body Body composition analysis often focuses on the tissue and whole body levels of multi-component model.

3. Behnke’s Reference Man • Storage fat averages ___% of body mass for young men. • Essential fat averages ___% of body mass for young men.

4. Reference Woman • Storage fat averages ___% for young adult women. • Essential fat averages ___% for young adult women. Four times greater essential fat for females relates to child-bearing.

5. Gross Composition of Body • Essential fat: fat in organs, muscle, CNS, bone marrow. Also includes sex-specific essential fat necessary for survival. • Storage fat: energy reserve includes visceral adipose tissue & larger subcutaneous depots. • Fat Free Body Mass and Lean Body Mass • In vivo (within a living organism), it isn’t possible to differentiate between essential and non-essential fat. • LBM =FFM (bone, muscle, organs, connective tissue) + essential fat. LBM is an in vivo entity. • Density of human fat is .901 g/cm3. FFM varies.

6. Gross Composition of Body • Density of FFM lower in children than adults. • Female density of FFM is lower at each age than male. • Percentage of FFM that is composed of water is higher in children.

7. Gross Composition of Body • Minimal body mass • What is suggested “healthy” lower level % fat in ? 3% • In females, includes 3% essential fat (same as ) + 9% sex-specific essential fat = 12%. • Optimal range of body fat should be established for each sport. • Elite female athletes in ballet, gymnastics, rowing, skating, track running events, triathlon body fat 8-15% • Underweight ≠ thin; appearance may average 18.2% body fat.

8. Leanness, Exercise, and Menstrual Irregularity • Lean:fat ratio may play role normal menstrual function. • Peripheral fat’s role in angrogens to estrogen • Production of leptin in adipose tissue • Factors associated with menstrual irregularity • High levels chronic physical stress causes hormone cascade • Nutritional inadequacy to sustain pregnancy • Too little fat triggers metabolic disturbances • Regional fat deposition

9. Methods of Body Composition Direct Assessment • Chemical dissolution: dissolves body into fat and fat-free components • Physical dissection: extensive dissection of cadavers.

10. Hydrostatic Weighing Air Displacement Skinfolds Girth Measurements Bioelectrical Impedance Analysis Dual-Energy X-Ray Absorptiometry Near Infrared Interactance Ultrasound Computed Tomography Magnetic Resonance Imaging Indirect Body Composition

11. Hydrostatic Weighing How is Archimedes principle of water displacement used to evaluate body composition? Loss of weight in water equals weight of water displaced which yields volume of water displaced @ any temperature. Example: 50 kg  2 kg @ 39.2F 48 kg @ 39.2F = 48,000 cm3 50 kg ÷ 48,000 cm3 = 1.0417g/cm3

12. Hydrostatic Weighing • Body Density = Mass ÷ Volume • Computing % body fat using population specific equation. • Limitations and Errors. • Air compartments in body. • Densities of FFM vary due to race, age, and athletic experience.

13. Air Displacement • Air displaced = Body Volume • Body density = mass ÷ volume • High validity compared to hydrostatic weighing

14. Skinfolds • Common field method • Relationships among selected skinfold sites and body density • Caliper exerts constant tension of 10 g/mm2 • Sum of skinfolds indicates relative fatness of individual

15. Girth Measurements • Uses 3 sites: see Appendix F • Men: right forearm, abdomen, right upper arm (<27) or buttocks (27+) • Women: abdomen, right thigh, right forearm (<27) or right calf (27+) • Pattern of fat distribution • Predicting Body Fat

16. Bioelectrical Impedance Hydrated, fat-free body tissues and extracellular water facilitate electrical flow compared to fat tissue because of greater electrolyte content of fat-free component.

17. Dual Energy X-Ray Absorptiometry • Two distinct x-ray energies penetrate into bone & soft tissue areas to depth of 30 cm. Computer software reconstructs an image of underlying tissue. • Quantifies bone mineral content, total fat mass, and FFM.

18. Body Mass Index • Importance of this easy to obtain index is its curvilinear relationship to all-cause mortality.

19. Near-Infrared Interactance • Uses technology developed by U.S. Dept. Agriculture to assess body composition of livestock and lipid content of grains. • Does not accurately predict human body fat across broad range of body fat levels.

20. Ultrasound Measures: • Assess thickness of different tissues • Obtain image of deeper tissues, e.g. muscle’s cross sectional area • It works by converting electrical energy through a probe into high frequency pulsed sound waves that penetrate the skin surface to fat-muscle interface.

21. Computed Tomography • Generates detailed cross-sectional, 2 dimensional radiographic images. • Passes x-ray beam through tissues of different densities. • Provides quantitative information on: • Total tissue area • Total fat and muscle area • Thickness and volume of tissues w/i organ

22. Magnetic Resonance Imaging • Electromagnetic radiation, not ionizing radiation, in strong magnetic field excites hydrogen nuclei of body’s water and lipid molecules. Nuclei then project detectable signal to visually represent various body tissues. • Provides quantitative information on total and subcutaneous adipose tissue.

23. Average Values for Body Composition • Average young male possesses between __ and __% fat. • Average young female possesses between ___ and ___ % fat.

24. Goal Weight • Goal weight should be based on body composition not stature. • Goal Weight = Fat Free Body ÷ (100 -% Desired Body Fat) • Desirable Fat Loss = Present body weight – Goal body weight

25. Percentage of Body Fat • Ballet dancers: 13-20 • Body builders: 10-15 • Triathlon: 10-15 • Jumpers: 10-18

26. Illustration References • McArdle, William D., Frank I. Katch, and Victor L. Katch. 2000. Essentials of Exercise Physiology 2nd ed. Image Collection. Lippincott Williams & Wilkins. • Plowman, Sharon A. and Denise L. Smith. 1998. Digital Image Archive for Exercise Physiology. Allyn & Bacon.