chapter 8: assessing body composition Flashcards
What is body composition?
The body is composed of fat mass and fat free mass
What is Fat Mass (FM)?
- All of the fat in the body
- Fats that can be extracted from the tissues in the body
- Can be called fat weight
What is Fat-Free Mass (FFM)?
- All fat-free tissues in the body including water (67% of FFM), muscles, bones, minerals, connective tissues, internal organs
- Can be called fat free weight
What is lean body mass? (LBM)
- Contains a small percentage of essentials fat stores
- Represents an in vivo entity that remains relatively constant in content of water, organic matter
What is the difference between LBM and FFM?
Fat free mass has no fat, LBM contains a small percentage of essential fats
What are the main categories of body fat?
Essential Fat and Nonessential Fat
Essential fat includes lipids in the:
- Nerves
- Heart
- Lungs
- Kidneys
- Intestines
- Bone marrow
- Brain
- Muscles
- Liver
- Spleen
- Mammary glands
- Lipid-rich tissues of the CNS
What are essential fats?
- Larger percentage in women: fat in breasts, uterus, etc., women have additional sex-specific essential fat
- Fat deposits are necessary for normal physiologic functioning in men and women
Where are non essential fats?
- Storage primarily found in fat cells (adipose tissue cells) either subcutaneously or vicerally
Adipose tissue contains about :
- 83% pure fat
- 15% water
- 2% protein
The amount of storage of fat depends on?
- Gender
- Age
- Heredity
- Metabolism
- Diet
- Activity level
Name the 2 Component Body Composition Models
- Skinfolds
- Hydrostatic Weighing (HW)
- Air Displacement Plethysmography (ADP)
What components do 2 component body composition models measure?
Fat component and Fat-Free Body component
Name 5 assumptions of the 2 component models of body composition
- Density of fat is 0.901 g/cm3
- Density of FFB is 1.100 g/cm3
- Densities of fat and FFB components (water,mineral, protein) are the same for all individuals
- Densities of various tissues composing FFB are constant within an individual and their proportional contribution to the lean component remains constant
- Individuals differ from the reference body ONLY in the amount of fat (73.8% water, 19.4% protein, 6.8% mineral)
These assumptions are not valid, the forst 2 differ for each individual and the last one can be affected simply by drinking water
Name the 3 component body composition models
- Bioelectrical Impedance Analysis (BIA)
- Dual Energy X-Ray Absorptiometry (DEXA)
What are the 3 components body composition measurements?
FM, FFM and component of fat free mass
Name the multiple component body composition models
- Computed Tomography (CT)
- Magnetic resonance Imaging (MRI)
Negative factor of CT
Ionized radiation (but measures fat distribution not just percentage)
FFB density varies with:
- Age, Growth, Sexual maturation, Gender, Ethnicity
- Levels of body fatness, physical activity level
- Number of diseases
FFB density depends on:
The relative proportion of water and mineral that compose the FFB
What are the Siri (1961) and Bozek et al. (1963) equations used to determine? What population would you use them on?
Estimation of % body fat, only to be used on caucasian males/females
Would you overestimate or underestimate your clients % BF if the FFB density was estimated to be greater than 1.100 g/cm3?
Underestimate
Would you overestimate or underestimate your clients % BF if the FFB density was estimated to be lower than 1.100 g/cm3?
Overestimated
Relative to the assumption of the 2 component model of body composition that FFB density is equal to 1.100 g/cm3, would you overestimate or underestimate the % BF for a black man or woman, a pro football player, a white child, or an elderly white man or woman?
- Overestimate the white child (lower mineral content and higher body water) and the elderly (lower mineral content)
- Underestimate the black man or woman and pro football player (higher mineral content and/or higher relative to body proteins)
Which methods of assessing body compositions are densiometric methods?
Hydrostatic weighing and air displacement plethysmograpgy
What is measured by densiometric methods?
Body volume
What principle is hydrostatic weighing based upon?
Archimedes’ principle:
- Water displacement states that “ a body immersed in water is buoyed up with a force equal to the weight of the water displaced”
- Weight loss under water is directly proportional to the volume of water displaced by the body’s volume
Hydrostatic Weighing
- Valid and reliable
- Widely used laboratory method for assessing total Db
- Provides an estimate of BV from the volume of water displaced by the body’s volume
What is body density?
Body Mass/ Body Volume
Is there an inverse relationship between Db and BV?
Yes
Is there an inverse relationship between Db and %BF?
Yes
What is tare weight?
The weight of the chair or platform and supporting equipment
What is gross underwater weight?
Tare wight + underwater weight
What is net underwater weight?
Gross UWW - Tare Weight
What measurements are needed to calculate Db using HW?
- Dry land weight
- Underwater weight
- Water density
- Residual lung volume
- Gastrointestinal tract volume
Is there an inverse relationship between water density and temperature?
Yes
What is Residual lung volume (RV)
- The volume of air remaining in the lungs after a maximal expiration
- Typically 1.0-2.4L
- Can be measured before, during or after
- Least affected by hydrostatic pressure
What is Functional Residual Capacity (FRC)
The volume of air remaining in the lungs at the end of a normal expiration
What is expiratory reserve volume? (ERV)
Maximal volume of air that can be expired from the lungs after a normal expiration
What is Total Lung Capacity? (TLC)
Volume of air in the lungs after a maximal inspiration
What methods are used to measure RV?
- Closed circuit approach: Oxygen, Nitrogen or Helium Dilution (based on normal gas volume in lung, normal breathing into machine, see how much oxygen is diluted)
- Open circuit approach: Nitrogen Washout (washing out the lungs with a known volume of gas)
Can RV be estimated using prediction equations?
Yes, different for males and females, depends on height and age
What value is assumed to be the gastrointestinal volume (GV) when the HW is used to assess body composition?
0.1L
What must be done to obtain a client’s correct body volume?
- Corrected BV: volume of water displaced without air in the body
- Subtracting (RV+GV) if measuring Db with RV)
What are the sources of error for hydrostatic weighing?
- Pretesting guidelines: No eating/strenuous exercise 4 hours before test, gas producing food 12 hours before the test
- Equipment calibration before testing (BW scale, load cells, gas analyzer for RV)
- Equipment used (UWW scale or load system)
- Measurements of BW, UWW and RV (more accurate when measured UWW and RV together)
- Client factors (motionless UW, maximal exhalation)
- Db calculated to 5 decimals
- Conversion formula
Is it better to use an UWW (autopsy or spring) scale or load cells to obtain accurate results with the HW method?
Load cells
Alternatives for client who cannot expel all the air from their lungs?
UWW at FRC
UWW at TLC
Alternatives for client who is fearful of being submerged, dislikes facial contact with water, is unable to bend forward to assume proper body position?
UWW at TLC with head above water level
Are body volume, Db, and % BF overestimated or underestimated when dry land weight, underwater wight, water temperature
- Dry-land weight and water temp = OVER
- BV, %BF OVER
- Db UNDER
- UWW and RV OVER
- BV, %BF UNDER
- Db OVER
What are the disadvantages of the HW (UWW) method?
- Time consuming
- Expensive equipment
- Adequate space, plumbing and high maintenance required
- Highly dependent on client (skill, cooperation, motivation)
- Some clients unable to perform
- Requires measurement of RV (additional equipment)
What is Air Displacement Plethymography (ADP) / what does it measure?
- Densiometric Method used for assessing body composition
- used to measure body volume and density
- uses air displacement to estimate body volume
Boyle’s Law
At constant temperature (isothermal condition) volume (V) and pressure (P) are inversely related
P1 and V1 are?
When the BOd Pod chamber is empty
P2 and V2 are?
When the client is in the Bod Pod chamber
V1-V2 is?
Volume of air in the empty chamber - volume of air remaining in the chamber when the client is inside = volume of air displaced when a client sits in the chamber
Sources of isothermal air that affect accuracy of Bod Pod test results?
- Excess body hair
- Excess facial hair
- Scalp hair
- More clothing
- Body (skin) surface area
- Thoracic gas volume
Sources of error of ADP testing
- Pretesting guidelines : (Same as HW testing)
- Swim suit and swim cap
- Body surface area (height : nearest cm, body weight: nearest 5g)
- Deviations in Normal Tidal Volume Breathing (affects BV and %BF)
- Performance of 2-point calibration (1. baseline calibration of empty chamber, 2. 50L calibration cylinder)
- Thoracic gas volume (measured better than predicted)
- Client factors (still for 20s)
Advantages of ADP?
- Quick to administer (5min)
- Minimal client compliance
- Minimal technician skill
- BodPod is mobile
- Accomodate special populations
Disadvantages of ADP?
- Expensive
- Only accessible in research facilities
- Special clothing
What factors must be corrected during ADP (Bod Pod) testing in order to obtain a client’s actual body volume?
- Estimation of body surface area corrects for the isothermal effects at the body surface
- Body volume must be corrected for thoracic gas volume
How does DEXA assess body composition?
- Estimates bone mineral, fat, lean soft tissue and visceral adipose tissue (VAT) mass at the whole body level and regional (trunk and appendicular) level
What is the procedure for DEXA?
- The subject lies supine on the table so that the source and detector proves pass across the body slowly
- 2 distinct low-energy X-Ray system penetrate bone and soft tissue areas in depth of about 30 cm
- Computer software reconstructs the attenuated x-ray beams to produce an image of the underlying tissues and quantify bone mineral content, total FM and FFM
Attenuation of DEXA?
- The loss of energy beam of radiant energy due to absorption
- Weakening of x-rays through fat, lean tissue and bone
disadvantage of DEXA?
- Expensive equipment
- Accessible in clinical or research settings
Factors affecting the accuracy of the DEXA results?
- Fasting prior to DEXA scan (increase accuracy)
- Sagittal abdominal diameter (use skeletal anthropometer to accurately determine body thickness
- Calibration of DEXA scanner (with marker provided by the manufacturer)
- Variability among DEXA technologies (high/low energy beams, imaging geometry, xray detectors, calibration methodology, algorithms, software versions
Field methods for assessing body composition?
- Skinfold method
- Bioelectrical impedance analysis
- Anthropometry method (girths, etc. )
- Ultrasound method
What is the bioelectrical impedance?
- Resistance to electrical current
- Greatest in fat tissue
- Least in fatfree tissue
What is the conductive pathway?
Greatest in tissues with greater amounts of water
Conduction
Inversely related to resistance
Impedance (Z)
- Opposition to flow current
- is a function of reactance and resistance
Resistance (R)
The opposite to current flow caused by the capacitance produced by the cell membrane
BIA indirectely estimates or predicts :
Fat free mass and total body water
Traditional BIA method measures?
The whole body resistance using a tetrapolar wrist-to-ankle electrode configuration
What do the “Tanita BI Analyzer” and the Omron BI Analyser” estimates?
%BF and FFM
What are the advantages of the BIA method?
- Rapid
- Relatively inexpensive
- Noninvasive
- Does not intrude upon clients privacy
- More comfortable
- Doesn’t require much technician skill
- Used in field settings
- Used to estimate body composition of obese individuals
What is not a major source of error of BIA measurement?
Technician skill, not major unless the standardized procedures for electrode placement and client positioning are not followed
What is a major source of error of BIA measurement?
- Client factors like Hydration level (major)
- Eating, Drinking, Dehydrating and exercice
- Menstrual cycle
- Large body weight gain due primarily to an increase in total body water (TBW)
Does an inverse or a direct relationship exist between resistance (R) and Skin temperature
Yes, inverse relationship.
What are the effects of eating, dehydration and aerobic exercice have on FFM?
- Eating (R measured 2-4hrs after: overestimates
- Dehydration: Underestimates
- Moderate intensity and low intensity: overestimates
What are the effects of eating, dehydration, and aerobic exercise have on %BF?
- Eating (R measured 2-4hrs after: underestimates
- Dehydration: overestimates
- Moderate intensity and low intensity: underestimates
What are the BIA pretesting client guidelines?
- No eating/drinking 4h before
- No moderate/vigorous exercise within 12h of test
- Void completely within 30 min of test
- No alcohol 48 hrs before
- Do not ingest diuretics, including caffeine before test (unless prescribed)
- Postpone for females during menstrual cycle stage where they retain water
Where are the electrodes placed for the BIA?
- Right side
- Source electrodes: 2nd and 3rd matacarpophalangeal joints, 2nd and 3rd metatarsophanlageal joint
- Sensory electrode: dorsal surface of wrist or ankle
- Sensory pick up electrodes sent by source electrodes
What is anthropometry?
The measurement of the size and proportion of the human body
What are anthropometric methods?
- Can be used to estimate body composition
- Assess total and regional body composition
Which anthropometric methods measure body size, body proportion ans assesses the sizes and proportions of body segments?
- Measure of body size: Body weight and height
- Measures of body proportions: Ratios of weight and height (ie BMI)
- Assessment of the sizes and proportions of the body segments: Circumferences, skin fold thickness, skeletal diameter and segment lengths
Which basic relationships are assumed when you use the skinfold method to estimate total body density in order to calculate the relative body fat?
A relationship exists between the sum of skinfolds and Db
What is indirectly measured by skinfolds?
The thickness of subcutaneous adipose tissue
What types of prediction equations have been developed to predict body density from SKF measurements?
- Population - specific SKF equations
- Generalized SKF equations
How many skinfolds are used in most equations to predict body density?
Most skinfold equations use the sum of 2 or 3 SKF sites (sites from upper and lower are used)
Do nomograms exist for some SKF prediction equations?
Nomograms exist to estimate %BF for some SKF prediction equations
What are the sources of error for SKF measurements?
- Technical skill
- Type of SKF calliper (select according to cost, durability, accuracy, precision and type used to develop a specific SKF equation)
- Calibration of calliper
- Client factors (hydration level, compressibility of adipose tissue)
Major source of error for SKF?
- Technician skill, a lack of intertechnician reliability
- Causes a low intertester reliability are improper location and measurement of SKF sites
- Need to practice on 50-100 clients to develop a high degree of skill and proficiency
- Minimum 2 measurements at each site (go through all then go back
Circumference (C)
- A measure of the girth of a body segment
- Affected by fat mass, muscle mass and skeletal size
Waist Circumference (WC)
- Useful measure of abdominal adiposity
- Predictor of obesity-related cardiometabolic disease
- Estimates health-related differences in cardiorespiratory fitness
- When coupled with BMI, predicts musculoskeletal injury risk and health risk better than BMI
Skeletal diameter (D)
- Measure of bony width or breadth
- Directly related to lean body mass (LBM)
- Important estimator of the bone and muscle components of FFM
Body mass index (BMI)
- Ratio of body weight squared (Wt/Ht^2)
- Assumes that a disproportionately heavy person is so because of excessive amount of fat mass
Waist-to-hip circumference ratio (WHR)
- Indirect measure of lower and upper body fat distribution
- Used as an anthropometric measure of central adiposity and visceral fat
- WC/HC
Waist-to-height ratio
- WC/standing height
- WC should be <1/2
Sagittal abdominal diameter (SAD)
- Measure of the anteroposterior thickness of the abdomen at the umbilical level
- More strongly related to risk factors for cardiovascular and metabolic diseases than WC, WHR, BMI
What are estimated by C, D, BMI, WHR, WHTR, and SAD, respectively?
- C: girth of a body segment
- D: used to classify frame size in order to improve the validity of height-weight tables for evaluating body weight
- BMI: body to height squared
- WHR: anthropometric measure of central adiposity and visceral fat
- WHTR: better indicator of adiposity and healthy risks than WC alone
- SAD: simple indicator of the amount of dysfunctional visceral adipose tissue in the body
What are the uses of the BMI?
- To classify individuals as obese, overweight or underweight
- To identify individuals at risk for obesity-related diseases
- To monitor changes in body fatness of clinical populations
What are the limitations of the BMI?
- Overestimates body fat in very muscular people
- Underestimate body fat in those who have lost muscle mass
- Gives high BMI for very short persons (<5 feet)
- Not a good measure of visceral fat (better measure of nonabdominal and abdominal subcutaneous fat)
- Does not provide information about body fat distribution
- Does not provide an assessment of body composition
- Factors such as age, ethnicity, body build and frame size affect relationship between BMI and %BF
What are the limitations of WHR?
- Women’s WHR is affect by menopausal status
- Not valid for evaluating fat distribution in prepubertal children
- Accuracy in assessing visceral fat decreases with increasing fatness
- May not detect changes in visceral fat accumulation
What influences hip circumference and waist circumference?
- HC only influenced by subcutaneous fat deposition
- WC affected by both visceral and subcutaneous fat depositions
What is the cutoff boundary value of WHTR?
- Recommended Optimal WHTR + Adult BMI:
- Men: 0.5 and 24
- Women: 0.26 and 26
Which anthropometric measure has been suggested as a better indicator of adiposity and health risks of WC alone?
Waist-to-Height Ratio
What is the purpose of using the Ashwell Body Shape Chart?
- Can be used to identify a client’s health risk based on body shape for:
- Men/Women
- People different ethnic groups
- Children 5&over
Which anthropometric measure is suggested to be an excellent measure of visceral fat?
Waist to Hip Circumference Ratio
Which anthropometric measure is more strongly related to risk factors for cardiovascular and metabolic diseases?
Sagittal Abdominal Diameter
What are the sources of anthropometric measurement error?
- Equipment:
- Type of skeletal anthropometer
- Improper maintenance
- Lack of periodic calibration
- Not using an anthropometric tape measure to measure circumferences
- Technician Skill:
- Not a major source of error for C and SD compared to SKF
- Must practice location and technique
- Intertechnician variability is small for circumference measurements
- Client Factors
- More difficult to obtain circumference measurements for obese individuals, circumferences are preferable to SKFs for measuring obese clients
- Accurate measurement of bony diameters in heavily muscled or obese individuals may be difficult
