chapter 4

Essential andStorage Fat

Techniques to Assess Body Composition

Determining Recommended Body Weight

Chapter 4Body Composition

Assessment

CHAPTEROUTLINE

Key TermsBody composition: The fat and nonfat components of the human body; important in assessing recommended body weightPercent body fat: Proportional amount of fat in the body based on the person’s total weight; includes both essential and storage fat




Lean body mass: Body weight without body fatRecommended body weight: Body weight at which there seems to be no harm to human health (healthy weight)

Key TermsOverweight: Excess body weight against a given standard such as height or recommended percent body fat; less than obeseObesity: A chronic disease characterized by excessive body fat in relation to lean body mass; usually at least 30% above recommended body weight

Essential fat: Minimal amount of body fat needed for normal physiological functions; constitutes about 3% of total weight in men and 12% in womenStorage fat: Body fat in excess of essential fat; stored in adipose tissue




Essential fat constitutes about 3% of the total weight in men and 12% in women

4.1Typical Body Composition of an Adult Man and Woman

Critical ThinkingJessica is a gymnast whose coach has asked her to decrease her total body fat to 7%. Can Jessica’s performance increase at this lower percent body fat?How would you respond to this coach?




Assessing Body CompositionResearch/medical facility techniques

Dual energy X-ray absorptiometry (DEXA) Magnetic resonance imaging (MRI)Computed tomography (CT)Total body electrical conductivity (TOBEC)




Assessing Body CompositionMore common techniques

Hydrostatic weighingAir displacementSkinfold thicknessGirth measurementsBioelectrical impedance




Dual energy X-ray absorptiometry (DEXA)Frequently used by research and medical facilitiesConsidered by many as the standard technique for body composition assessmentUses low-dose beams of X-ray energyMeasures fat mass, fat distribution pattern, and bone density

DEXAProcedure is simple; takes only 15 minutes to administerNot readily available to most fitness participants




Hydrostatic WeighingUnderwater weighingMost common technique used for decadesA person’s “regular” weight is compared with underwater weightFat is more buoyant than lean tissueAlmost all other indirect techniques have been validated against hydrostatic weighing




Hydrostatic Weighing Drawbacks

Time consumingNot feasible to test large number of peopleRequires measurement of residual lung volume (if unknown, can be estimated)Difficult to perform on the aquaphobic




Air DisplacementIndividual sits inside small chamberComputerized pressure sensors determine the amount of air displaced by the personBody volume is calculated by subtracting the air volume with the person inside the chamber from the volume of the empty chamber (air in the lungs is taken into consideration)Body density and percent body fat are then calculatedLess cumbersome to administerTakes only about 5 minutes




Skinfold ThicknessBased on the principle that approximately half of the body’s fatty tissue is directly beneath skinReliable measurements of this tissue give a good indication of percent body fatSkinfold test is done with pressure calipersSeveral sites are measured and percent fat is estimated from the sum of the three sites using Tables 4.1 (women) and 4.2 or 4.3 (men)All measurements should be taken on the right side of the body




4.3Anatomical Landmarks for Skinfold Measurements

Chest

Abdomen

TricepsSuprailium

Thigh

Skinfold Thickness




4.1Skinfold Technique:

Percent Fat Estimates for Women

4.2Skinfold Technique:

Percent Fat Estimates for Men under 40

Girth MeasurementsRequires a standard measuring tapeWomen: Upper arm, hip, and wrist measurements (cm)

Look up constants on Table 4.4 based on measurements and determine body density and percent fat according to predicting equations

Men: Waist and wrist measurements (inches)Use Table 4.5 for percent body fat estimate




4.4Girth Measurement: Conversion Constants to Calculate Body Density for Women

4.5Girth Measurement: Estimated Percent Body Fat for Men

Bioelectrical ImpedanceSimpler to administer, but accuracy is questionableSensors are applied to the skin and a weak electrical current is run through the body to estimate body fat, lean body mass, and body waterBased on the principle that fatty tissue is a less-efficient conductor of an electrical currentThe easier the conductance, the leaner the individualBody weight scales with special sensors on the surface may also be used to perform this procedure




4.10Body Composition Classification according to Percent Body Fat

Body Mass Index (BMI)Incorporates height and weight to estimate critical fat values at which disease risk increases

BMI = Body Weight (lbs) x 705 ÷ (height in inches)2

ExampleBody Weight = 172 lbs Height = 67 inchesBMI = 172 x 705 ÷ (67)2 BMI = 27




4.7Disease Risk according to BMI

Even though the risk for premature illness and death is greater for those who are overweight, the risk also increases for individuals who are underweight

4.6Disease and Mortality Risk Based on BMI

4.7Overweight and Obesity Trends inthe United States

Waist CircumferencePredicts disease risk according to the way people store fat (waist versus other areas)

Disease Risk according to WC

4.8

Essential and

Storage Fat


Determining Recommended Body

Weight

Waist-to-Hip RatioPredicts disease risk according to “apple” or “pear” shape

Disease Risk according to Waist-to-Hip Ratio

4.9

Essential and

Storage Fat



Weight

Because of the typical reduction in physical activity, each year the average person gains 1.5 lbs of body fat and loses a half a pound of lean tissue

15.8Body Composition Changes for Adults in the U.S

Recommended Body Weight Determination

Determine pounds of body weight that are fat (FW):multiply body weight (BW) by current percent fat (%F)(FW = BW x %F)Determine lean body mass (LBM):subtract weight in fat from total body weight(LBM = BW – FW)Select a desired body fat percentage (DFP) based on health or high fitness standards given in Table 4.9Compute recommended body weight (RBW) according to the formulaRBW = LBM ÷ (1.0 – DFP)

Essential and

Storage Fat



Weight

Recommended Body Weight Determination: Example

Sex: femaleAge: 19BW: 160 lbs%F: 30% (.30 in decimal form)

FW = BW x %FFW =160 x .30 = 48 lbsLBM = BW – FWLBM =160 – 48 = 112 lbsDFP: 22% (.22 in decimal form)RBW = LBM ÷ (1.0 – DFP)RBW =112 ÷ (1.0 – .22)RBW =112 ÷ .78 = 143.6 lbs

Essential and

Storage Fat



Weight

Critical ThinkingHow do you feel about your current body weight and what influence does society have on the way you perceive yourself in terms of your weight?Do your body composition results make you feel any different about the way you see your current body weight and image?

Essential and

Storage Fat



Weight

Loss of lean body mass can be offset or eliminated by combining a sensible diet with physical exercise

4.9Effects of a 6-Week AerobicsExercise Program on Body Composition

End of Chapter

chapter 4

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