Body Composition

Exercise PhysiologyMcArdle, Katch, & Katch – Ch. 16

Gross Composition of Human Body

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

Behnke’s Reference Man

Storage fat averages ___% of body mass for young men. Essential fat averages ___% of body mass for young men.

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.

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.

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.

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.

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

Methods of Body Composition

Direct Assessment Chemical dissolution: dissolves body

into fat and fat-free components Physical dissection: extensive

dissection of cadavers.

Indirect Body Composition Hydrostatic

Weighing Air Displacement Skinfolds Girth

Measurements Bioelectrical

Impedance Analysis

Dual-Energy X-Ray Absorptiometry

Near Infrared Interactance

Ultrasound Computed

Tomography Magnetic

Resonance Imaging

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 @ 39.2F48 kg @ 39.2F = 48,000 cm3 50 kg ÷ 48,000 cm3 = 1.0417g/cm3

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.

Air Displacement

Air displaced = Body Volume Body density = mass ÷ volume High validity compared to hydrostatic

weighing

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

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

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.

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.

Body Mass Index

Importance of this easy to obtain index is its curvilinear relationship to all-cause mortality.

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.

Ultrasound

Measures:1. Assess thickness of different tissues2. 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.

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

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.

Average Values for Body Composition

Average young male possesses between __ and __% fat.

Average young female possesses between ___ and ___ % fat.

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

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

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.