Body Composition Assessment Methods (WEEK 10)

Assumptions of Skinfold Method

-fat patterning -relationship between internal and external fat -skin thickness -skinfold compressibility -lipid fraction of adipose tissue -water content of adipose tissue

Importance of body composition (health related)

-identify health risk -clients understanding of health risk with lean mass -monitor changes in body comp -understand and improve self esteem + confidence

Importance of body composition (performance related)

-identify optimal lean mass + fat mass to achieve ^ performance -categorize group based on specific reference standards -monitor growth, development in relation to body comp +athlete -formulate effective exercise + nutrition invertentions aiming to improve

underwater weighing equations

-inaccuracies in hydrod are due to variation in the density of the FFM from one individual to another -age, sex, race affect the density of fat free mass -thus having specific equations ^

how it works

-measures pressure changes with injection of known volume of air into closed chamber -large body vol displaces air volume in chamber which results in bigger increase in pressure with injection of known volume of air

skin fold method advantages

-measures subcutaneous fat -useful for teams/large groups -portable -relatively inexpensive -validated against hydrodensitometry method

underwater weighing disadvantages

-most participants not comfortable blowing all their air out esp children -ambulatory problems eg elderly getting into tank -time consuming

underwater weighing sources of error

-not getting all air out -reading scales wrong -not using correct equations

reliability and disadvantages of antropmetric techniques is affected by:

-precise identification of skin fold/ pressure when measurement taken/ proper timing and release of caliper jaws -type of caliper -subject factors (compressibility, distrubution) -prediction equation (age, race, sex, level of physical activity)``

body mass index advantages

-quick -widely used predictor cv disease and type 2 diabetes -basic equp needed -cheap

general research approach for doubly indirect methodologies:

-select a specific sample -determine body density or % fat using a reference methodology -measure participants with a new different technique -produce regression equations to best predict density or % fat from new technique

air displacement plethysmography advantages

-subject availability -precision -less time-consuming than underwater weighing and requires less technical skills -more accommodating and available

underwater weighing advantages

-valid, reliable + popular in lab methods -predictive error < 1-2% BF when RV is measured -many equations specific to each group

WHR disadvantages

-whr of women affected by menopause -not valid for evaluating fat distrubution in pre pubertal children -WHR may not accurately detect changes in visceral fat accumulation

estimating body fat from skinfolds

1. measure the skinfolds precisely using guidelines 2. calculate body density using relevant equations 3. use appropriate equation to calculate body fat % -indirect measure the thickness of subcutaneous adipose tissue

BIA: basic theory

1. the human body is a perfect cylinder with uniform length + cross sectional area 2. the impedance to a current is directly related the length of the conductor + inversely related to its cross sectional area 3. biological tissues act as conductors or insulators and the flow will follow the path of least resistance 4. impedance is a function of resistance and reactance (opposition to flow caused by a cell membrane)

multicompartmental x ray absorptiometry

2 different energy level x rays

underwater weighing

A method of estimating total body fat by weighing the individual on a standard scale and then weighing him or her again submerged in water. The difference between the two weights is used to estimate total body volume.

body density calculation

Durnin (1974)- four sites, illiac crest, subscapular, triceps, biceps body density= 1.1581 - 0.072 x log (^4) women 1.161 - 0.06 x log (^4) men

Air Displacement (Bod Pod)

Measures total body air displacement Used with other measures for a full assessment

Two component model of body fat % equations

Siri (1961) = %BF = (4.95 / Db - 4.50) x 100 Brozek (1963)= %BF = (4.57 / Db. - 4.142) x 100 yield similar %BF= ranging 1.03 to 1.09 g cc-1 training is necessary to ensure low technical error of measurement (TEM)

Archimedes' Principle

States that the buoyant force is equal to the weight of the fluid displaced by an object.

Waist-to-Height Ratio (WHtR)

The ratio of waist circumference to height. For young people, ratios greater than .5 predict reduced life expectancy and greater likelihood of obesity-related diseases. Ratios greater than .6 are considered to be more urgent indicators of future problems. Ratios less than .4 may predict problems caused by emaciation.

dual energy x-ray absorptiometry

Uses x-rays to measure bone, fat, and fat-free mass

air displacement plethysmography

a process for measuring body composition that utilizes the inverse relationship between pressure and volume to measure body volume directly

Bioelectrical Impedance Analysis (BIA)

a technique that distinguishes lean and fat mass by measuring the resistance of various body tissues to electrical currents

direct segmental multi frequency BIA (DSM- BIA)

analyze body in 5 distinct sections independantly: 2 arms, 2 legs and torso

doubly indirect methods

anthropometry skinfold thickness BMI ultrasound measurements bioelectrical impedance analysis (BIA) total body electrical conductivity

Densitometry

body density (Db) = mass / volume unitd = kg/l

process and expected results of underwater weighing

determine body vol -> calculate body density -> calculate % fat (equations using siri/bozek) -if body vol high -> body density low -> fat % higher -if body vol low -> body density high -> fat % lower

BIA disadvantages

differences in equipment, body water level and skin temp can effect accuracy, need equation

determining residual volume

equations based on height and/or vital capacity

assumptions of fat and fat free component

fat component- fat (adipose) + neural +essential fat (density 0.9. g/ml) ff component- lean mass + bone mass + tendons + organs + water (density 1.1 g/ml)

residual vol predictions:

male = 0.24 x VC female = 0.28 x VC male = 0.019 x (height cm) + 0.0115 x (age - 2.24) female = 0.023 x (height cm) + 0.021 x (age - 2.978)

Sagittal Abdominal Diameter (SAD)

measure of the anteroposterior thickness of the abdomen at the umbilical level <25cm w/ normal BMI >30cm indicates ^ coronary disease risk

bia analyzers

omron, tanita, bodystat

BIA advantages

quick and easy to use, portable, low cost

Boyle's Law

the pressure + vol. of a given mass of confined gas are inversely proportional

bia frequencies

time delay -> reactance (current encounters cell wall) + water in body will resist flow of current = impedance lower frequencies don't have energy to pass cell walls easily -> better suited for measuring extracellular water higher frequencies can penetrate walls + measure extra/intra cellular water

Waist-to-hip ratio (WHR)

waist or abdominal circumference divided by the hip or gluteal circumference; method for assessing fat distribution -WHR values >0.94 for men and >0.82 for women are high risk for adverse health consequences -location of waist size not universally standardize

underwater weighing explained

±2.5% if done w/ experienced participants body density= body weight. body volume body weight= measured on regular scale body volume= volume of water displaced vol of water displaced= body weight - underwater body weight/ water density body density affected by air left in lungs (residual vol) + gastrointestinal (GI) tract

BIA Equations

% BF = (BW - FFM)/BW x 100

Importance of body composition

- determines appearance - affects self concept - related to working capacity - excess weight adds to workload - excess fat limits range of motion - obesity places one at risk of diseases

indirect methods to predict body fat %: Densitometry methods

- underwater weighing (hydrodensitometry) -air displacement plethysmography (ADP) -dual energy X-rau absorptiometry (DXA) -medical resonance imaging (MRI) -computed tornography (CT)

dual energy x ray advantages

-accurate and now considered the 'gold standards' -clinical measurement of bone mineral content (osteoporosis) -safe and rapid -minimal subject cooperation -low radiation exposure

anthropometric methods

-body mass index -circumferences -skinfold measurements/body diameters

dual energy x-ray absorptiometry details

-calibration standards (acrylic, aluminium, delrin) are measured -lean, fat and bone mass each reduce the xray signal for each point in the image + calculated by direct comparison to the standards -whole body and site specific results -osteoporosis official clinical diagnosis

direct methods of body composition

-chemical analysis of carcasses -dissection: Brussels Cavader Study

air displacement plethysmography disadvantages

-costs 20-25k pounds -assumption of constant density of FFM and FM for prediction of % body fat from whole body density -assumption that Bod Pod controls the isothermal effects of clothing, hair, thoracic gas volume, and body surface area

dual energy dissadvantages

-costs 35-40k pounds -limited access -results may vary with manufacturer, model and software version

body mass index disadvantages

-doesn't account for composition of the body -potential misclassification of under, pver and obese status