Body Composition

what is excess BF associated with?

-Excess body fat is associated with many chronic conditions.

*remember that BMI is an ACSM risk factor (high BMI=higer risk)

what % of Americans or OW or Obese? % of Children?

-Approximately 70.2% of American adults are classified as either overweight or obese, and more than a third (37.7%) are classified as obese.

-Nearly one-third (31.8%) of American children and adolescents are overweight or obese.

*carry into adulthood; genetic factors

Health-related changes in body composition that accompany aging:

-Increasing body fat

-Decreasing bone mineral density

-Sarcopenia (muscle wastes away)

*Heart Failure ex: normal BMI, but high BF and low LBM

Two-component model

-Expressed as the relative percentage of mass that is fat (FM) and fat-free (FFM) using a two-component model

-Estimated with methods that vary in terms of complexity, cost, and accuracy

-general considerations when weighing someone

-units for BMI

-what does BMI fail to distinguish?

-Calibrated scale with individual wearing minimal clothing, empty pockets, and no shoes

-BMI (kg/m²): body weight (kilograms) / height (meters squared)

-Fails to distinguish between body fat, muscle mass, and bone

*just gives overall distribution

circumferences

-Quantify body fat distribution, especially of the waist and hip

-Equations to predict body fat percentage from circumference measures (standard error of estimate [SEE]=2.5%-4.0%)

*BMI + circumference: most of what need to know risk factor

android obesity vs gynoid obesity

-Android obesity (more abdominal fat) increases risk of chronic diseases compared to gynoid obesity (more fat in hip and thigh)

-Visceral vs. subcutaneous fat

waist to hip measurement procedure

Anatomic Origins and Methodology for Body Circumference Measures

*wasit to hip

Waist-hip ratio: how measure + risk associated with certain #/s

-Waist-to-hip ratio (WHR): circumference of waist (above the iliac crest) divided by the circumference of the hips (buttocks/hips)

-Health risk increases as WHR increases, and the standards for risk vary with age and sex.

•Younger than 60 years: very high health risk for men with WHR >0.95 and women with WHR >0.86

•60-69 years: very high health risk for men with WHR >1.03 and women with WHR >0.90 (*slightly higher)

*generally, >1= lot of mass in abodmen

-Waist circumference: indicator of obesity-related health risk because of central obesity as the primary health issue (*central obesity= higher risk CAD)

-Similar limitations as BMI

BMI classifications

*>30=ACSM RF/obese

*>25= OW

*<18.5= higher risk as well (bc can’t fight disease as well; contraversal for people with cystic fibrosis, cancer, etc.)

true or false: BMI and waist circumference are simple antroprometric measures for body comp?

true! (height and weight → calc BMI)

*skin folds are NOT

what are skin fold measurements used for? based on what prinicple? sites?

-Estimates body fat percentage by determining thickness of several folds of skin across body

*NOT a simpe antro measure!

-Principle: amount of subcutaneous fat is proportional to total amount of body fat

•~1/3 of total fat in body is located subcutaneously

•Exact proportion varies with sex, age, and race

what are the pros and cons of skin folds?

-Pro: Correlates well (r = 0.70–0.90) with hydrodensitometry, air displacement plethysmography, and dual-energy X-ray absorptiometry (DXA) values

-Con: ~±3.5% accuracy, but need skill to be accurate; generally has higher amount of body comp error

skinfold measurement procedures

-All measurements should be made on the right side of the body with the individual standing upright.

-Caliper should be placed directly on the skin surface, 1 cm away from the thumb and finger, perpendicular to the skinfold, and halfway between the crest and the base of the fold.

-Pinch should be maintained while reading the caliper.

-Wait 1–2 seconds before reading caliper.

-Take duplicate, but not consecutive, measures at each site, and retest if duplicate measurements are not within 1–2 mm.

Factors that may contribute to measurement error within skinfold assessment

-Poor anatomical landmark identification

-Poor measurement technique 

-An inexperienced evaluator

-An extremely obese or extremely lean individual (doesn’t work for one extreme or the other; same for all body comp measures)

-An improperly calibrated caliper (so calibrate beforehand with known mm block)

Densitometry

-Estimate of total body fat percentage derived from a measurement of whole-body density using the ratio of body mass to body volume

-Used as a reference or criterion standard for assessing body composition for many years

-Limiting factor: accuracy of the body volume measurement because body mass is measured simply as body weight

Hydrodensitometry

-Hydrodensitometry (underwater) weighing is based on Archimedes principle: When a body is immersed in water, it is buoyed by a counterforce equal to the weight of the water displaced.

•Bone and muscle tissue are denser than water, whereas fat tissue is less dense (more non-fat=sink)

•Loss of weight in water allows for calculation of body volume

*scale in tub, blow out all air in lungs; not used much anymore

-When two individuals have the same total body mass, the individual with more fat-free mass (FFM) weighs more in water and has a higher body density and lower percentage of body fat compared to the individual with less FFM.

*labor intensive, but good if patient compliment; not good for people w/ lung disease, lean people

Plethysmography

-Air displacement in a closed chamber

-Uses a dual-chamber plethysmograph that measures body volume by changes in pressure in a closed chamber

*”Bod Pod”

Conversion of Body Density to Body Composition

*determine body density → plug into equation → get body comp

-Percent body fat can be estimated once body density has been determined.

-Prediction equation to estimate percent body fat from body density using the two-component model of body composition:

•ex: [(4.95 / Db) – 4.50] X 100

-Age, gender, race, training status, and certain disease states may affect the density of FFM (much of this variance related to the bone mineral density component)

DXA

-Dual-energy X-ray absorptiometry (DXA)

-gold standard

-measured bone mineral density and body comp; measures water content as well

BIA

-Bioelectrical impedance analysis (BIA)

•Similar accuracy as skinfolds

•Stringent protocol adherence

*current enters 1 electrode and exits other, faster if more muscle (slower if more fat)

*measures water content as well; readily available and less expensive than DXA

*2 site or full body/4 site

*don’t do if have pacemaker, should be okay if pregnant, messed up by menstral cycle?

ultrasound + smartphone applications

-ultrasound: superficial layer to get body comp

-phone prob not best

Body comp norms

-No universally accepted norms for body composition

-Satisfactory for health:

•12%–23% for men

•17%–26% for women

-Age and race also impact what may be construed as a healthy percent body fat.