Fitness prog. Chapter 8

Relative Body fat %BF

classifies level of body fatness

Men % BF spectrum for 20 to 29 years old

minimal: 3.0%

average: 13.5%

Excessive: >22.0%

women % BF spectrum for 20 to 29 years old

minimal: 10.0%

average: 20.0%

excessive: >32.0%

Classification and uses of body composition measures 

• estimates healthy body weight 

• Estimate competitive body weight for athletes

• monitor growth of children and adolescents 

• assess changes in body composition related to the following:

  • aging

  • poor diet

  • disease status

whole body 

fat+fat free body 

assumptions

1. density of fat = 0.901 g*cc-1

2. density of FFB= 1.10 g*cc-1

3. densities of fat and FFB components (water, proteins, mineral) are same for everyone

4. densities of the various tissues composing the FFB are constant within an individuals

5. individual being measured differs from the references body only in the amount of body fat

basis for hydrodensitometry (underwater weighing)

• proportions of FFB constituents

  • water 73.8%

  • protein 19.4%

  • mineral 6.8%

• Equations converting body density (Db) from HW to %BF

  • siri (1961)

  • Brozek etal.

(most commonly used)

FFB density known to vary

• age

• sex

• ethnicity

• physical activity

• % BF

• variance due to % water and % mineral within FFB

• 2c models are densitometric models

body composition: multi components models 

• eliminate much of guesswork in 2c model assumptions

• measure % water or % mineral in addition to FM and FFM 

• Useful for developing population specific formulas 

Laboratory Methods for assessing body composition

• use expensive equipment, limited in accessibility

• require skilled technicians

• serve as criterion measures

• commonly used methods include

  • hydrostatic weighing (HW) with measured residual long volume (RV)

  • air displacement plethysmography (ADP)

  • dual energy x-ray absorptiometry (CXA)

hydrostatic weighing (HW)

• valid and reliable densitometric method 

• estimates body volume (BV)

• requires total body submersion 

• computation of Db 

  • Db=total body mass/BV

• Residual long volume (rv) measurement increases accuracy

• Pretest guideline adherence a must

Hydrostatic weighing testing guidelines 

• calibrate scales 

• have client void completely and change into swimwear

• record tare weight, water temperature, and water density 

• measure client’s dry weight 

• have clinet shower 

• have client enter HW tank and remove trapped air bubbles 

• give tips for maximal exhalation technique and being still underwater 

• record and average the three heavist, consistent underwater weights with ± 100g 

• complete calculations

air displacement plethysmography (ADP)

• viable alternative densitometric method for HW

• Requires minimal client compliance and technician skill

• based on Boyle’s law of pressure volume relationships 

• body surface (BSA) correction 

• thoracic gas volume (TGV)

  • measured= best

  • predicted=faster

  • pretest guidelines similar to those for HW

ADP testing procedures

• warm-up and calibrate Bod Pod

• have client void and change into dry, form-fitting swimwear 

• measure client height

• enter client demographics into computer and select DB to %BF conversion 

• Follow computer’s prompts 

• posture, movement, pressure changes sensed by ears

• if measuring TGV, give client tips for success with the procedures

  • may require several attempts

  • accounts for individual variation from predicted TGV algorithm

• record or print computer output

Dual energy x-ray absorptiometry

• three components (3C) model

• uses two x-ray beam frequencies 

• low radiation exposure 

• minimal client effort 

• best method to estimate mineral contribution to FFB 

• result vary across DXA analyzers

• technician training and qualification requirements vary by state 

• medical supervision of technician varies by state 

Field methods for assessing body composition

• practical time-efficient portable alternatives to lab methods

• several options

  • skinfold thickness assessment

  • ultrasound

  • bioelectrical impedance analysis

  • anthropometry

skinfold method

• invasive method

• indirect measurement of subcutaneous body fat

• assumptions

  • SKF is a good measure of subcutaneous fat

  • distribution of subcutaneous and interla fat is similar for all of the same sex

  • sum of SKFs from multiple sites usable to estiamte total body fat

  • relationship exists between SKF and Db

  • age is independent predictor of Db for adults

• good technicans get SKF result within ± 3.5% BF of HW

• extensive practice and impeccable technique are key

• may not be appropriate for assessing %bf of clients with grater obesity level

skinfold method-population specific Db equations

• based on linear relationship between SKF and Db 

• underestimate %BF in fatter clients

• overestimate %BF in leaner clients 

skinfold method-generalized Db equation

• quadratic equation

• developed on heterogeneous subject pool

• caution when using equations developed with DXA criterion

most SKF equations validated against HW at measured RV

assumptions of 2C model apply

most SFK equations use sum of two or three SKF sites

sites from both upper and lower body

Skinfold method - major source of error 

• technician skill

• type of SKF caliper

• client factors 

be attentive to span of thumb and index finger, direction of fold and placement of caliper jaws

continuously work on interpersonal communication skills 

ultrasound 

• noninvasice alternative to SKF 

• uses many of same sites as SKF

• hand held want probe sends and receives sound signals 

• two types of signal images

  • line drawing of amplitude (a-mode)

  • horizontal bands of varying brightness (B-mode)

ultrasound: source of measurement error 

• technician 

• mode of ultrasound 

• signal frequency 

• sound speed 

Bioelectrical impedance analysis

• noninvasive

• combination of pairs of sending and receiving electrodes

• low-level current passed between electrode pairs

• tissue either interfere (impeded) or conduct electrical currents

• total body water (TBW) volume inversely related to resistance of currents

• 2c model assumption regarding % water in FFB applies

• Indirectly estimates fat-free mass (FFM) and TBW

  Assumptions

  1. Body is perfect cylinder, uniform in length and cross-sectional area

  2. Assuming 1 is true:

  • Impedance (Z) directly related to height and inversely related to CSA at fixed signal amplitude

  • Tissue-specific resistance to current assumed constant

  3. Tissues are current conductors or insulators; current seeks path of least resistance

  4. Z is the mathematical function of resistance and reactance

  • Resistance (R): pure current opposition

  • Reactance (Xc): opposition due to cell membrane storage of electrical capacity

bioelectrical impedance analysis -body 

• supine, tetrapolar, ( 4 electrodes: 1 on each hand and each foot)

• upper body (4 electrodes: 2 per handle)

• lower body (4 electrodes:2 per handle)

• whole body vertical (8 electrodes: 2 per hand, 2 per foot)

bioelectrical impedance analysis (protocol)

• client hydration status is key

• must adhere to standard BIA pretesting guidelines

• use caution interpreting proprietary displays of FFM and % BF

• predictive accuracy similar to that of skf

• Better than SKF if client is obese (Excessive adipose tissue)

bioelectrical impedance analysis sources of measurement error

• analyzer used

• client factors

• technician skill

• environmental factors

• FFM prediction equation

anthropometric methods 

• based on body size and proportions 

• assist in classifying disease risk 

  • methods

    • bdoy mass index

    • circumferences

    • skeletal size

Anthropometric Methods

• used to classify body weight and body fat levels 

• cannot differentiate fat deposition locations 

• May result in misclassifications 

• traditional european and U.S. cut points invalid for many ethnic groups 

Anthropometric Methods circumferences 

• measures of girth 

• affected by everything beneath the tape measure 

• use anthropometric tape measure to increase accuracy

Anthropometric Methods waist circumference

• measure of abdominal adiposity

• no standard waist location

Anthropometric Methods waist to hip ratio

• indirect measure of fat deposition pattern 

• apple versus pear 

Anthropometric Methods waist to height ratio

• better adiposity indicator than waist circumference alone 

• waist should be <50% of height

Anthropometric Methods sagittal abdominal diameter 

• anteroposterior thickness at umbilical level 

• assumption for DXA procedure

Anthropometric Methods skeletal diameters

• classify frame size

• improve estimates of anthropometric %BF result

• standard anatomical landmarks

anthropometric methods - sources of measurement error

• equipment

• technician skill

• client factors

% body fat/TBW goals

• assess current body weight

• assess current % fatness

• choose reasonable goal 

ex: 25 yr old male, 90kg, 25% goal is 20% fat