Scientific Basis of Body Composition Analysis Flashcards Preview

DPT 728 Clinical Exercise Physiology > Scientific Basis of Body Composition Analysis > Flashcards

Flashcards in Scientific Basis of Body Composition Analysis Deck (28)
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1
Q

Intro

A
  • body comp is key component of health and physical fitness
  • assessment of percentages of lean and adipose tissues
  • many methodologies available
2
Q

Role of Fat in Normal Physiology

A
  • phospholipids needed for cell membrane formation
  • thermal insulation
  • storage of fuel
  • transport and storage of fat soluble vitamins: A, D, E, and K
  • also serve role in nervous system, menstrual cycle, growth and maturation during puberty
3
Q

Body Composition and Clinical Analysis

A
  • overweight and underweight pose many health risks
  • these conditions present special clinical and public health challenges
  • obesity reaching epidemic status in our society
4
Q

Associated Risks of Obesity

A
  • coronary artery disease
  • hypertension
  • NIDDM
  • chronic obstructive pulmonary disease
  • osteoarthritis
  • certainforms of cancer
5
Q

Conditions Linked to Too Little Bodyfat

A
  • anorexia nervosa
  • bulimia nervosa
  • dysmorphia
  • exercise addiction
  • certain diseases such as cystic fibrosis
6
Q

Classification and Uses of Body Composition Measures

A
  • percent body fat or relative body fat is used
  • minimum, average, and obesity values vary with age, sex, activity status
  • average body fat values: males 13% females 28% for ages 18-34
7
Q

Additional Uses for Body Composition Measures

A
  • estimating healthy body weight and formulating nutritional recommendations
  • estimating competitive body weight for athletes
  • monitoring growth of children and adolescents
  • identifying kids at risk of under or over fatness
  • assessing changes in %BF associated with aging, malnutrition, certain diseases
  • assessing efficacy of nutritional and exercise interventions to remedy these changes
8
Q

Body Composition Models

A
  • uses 2 component model
  • divides body into fat and fat free mass
  • fat free mass consists of water, muscle, bone, internal organs
  • basisfor hydroensiometry
  • equations derived to compute individual’s total body density
  • Db determined from hydrostatic weighing and then converted to % BF
  • 2 component model accurate as long as assumptions are met
  • no guarantee of FFM of individual in certain population will exactly match reference body
  • FFM varies with age, sex, ethnicity, level of body fatness, physical activity level
  • multi-component models exist for certain population subgroups
9
Q

Assumptions of 2 Component Model

A
  • density of fat=.901 g/cc
  • density of FFM=1.1 g/cc
  • densities of fat and FFM are same for all individuals
  • densities of tissues within an individual are constant
  • proportional contribution of lean tissues are constant (assume everyone is uniform)
10
Q

Hydrostatic Weighing

A
  • valid, reliable and widely used
  • based on Archimedes’ principle
  • total Db is calculated by dividing body mass by body volume
11
Q

Guidelines for Hydrostatic Weighing

A
  • body volume is assessed by totally submerging body
  • underwater weight taken
  • body volume must be corrected for lung residual volume
  • also correct for air in GI tract assumed to be 100 ml
  • wear lightweight swimming suit
  • urinate and eliminate as much feces as possible before testing
  • calibrate HW scale or load cell system
  • weight chair or platform under water
  • water temp should range between 34* and 36*
  • remove all air bubbles from swim suit and hair
  • exhale as much as possible when submerged in tank
  • remain as motionless as possible
  • administer 3-10 trials
  • determine UWW by subtracting weight of chair or platform
12
Q

Special Considerations for Hydrostatic Weighing

A
  • some clients are unable to blow out all air from lungs
  • some clients are afraid to put face in water
  • some clients are not flexible enough to get back and heads fully submerged
  • estimating RV greatly decreases accuracy
  • menstrual cycle can greatly affect estimates of %BF
13
Q

Air Displacement Plethysmography

A
  • aka bod pod
  • used in laboratory and clinical settings to measure BV and estimate dB
  • used to measure air displacement
  • also measures pressure-volume relationships to derive BV
  • BV is equal to air volume of empty chamber-volume of air in chamber with client in it
  • method is quick and requires minimal client compliance
  • sits in pod and breathes normally
  • good test-retest reliability and acceptable validity in old studies
  • new studies show mixed results so more research is needed
14
Q

Dual-Energy X-Ray Absorptiometry

A
  • Gaining acceptance as a reference method for body comp assessment
  • method yields estimates of bone mineral, fat, lean soft tissue
  • high degree of agreement between HW and DEXA
  • attractive alternative because it is safe and quick-total body scan takes 10-20 minutes
  • requires minimal subject cooperation
  • importantly accounts for individual variability in bone mineral content
  • further research needed before DEXA can be firmly established as the best gold standard
  • often used a lot for aging women with osteoporosis
15
Q

Filed Methods for Assessing Body Composition

A
  • allow for more practical assessment of body composition
  • must understand basic assumptions to use methods and equations properly
  • must follow standardized testing procedure
  • must practice in order to perfect measurement technique for each method
16
Q

Skinfold Method

A
  • sum of skinfolds (SSF) indirectly measures thickness of subcutaneous adipose tissue
  • different forms of SSF prediction equations are available: linear (population specific) or quadratic (generalized)
  • 100+populations-specific equations exist
17
Q

Assumptions of SSF

A
  • SSF is a good measure of subcutaneous fat
  • distribution of fat is similar for all individuals within each sex
  • SSF can be used to estimate total body fat secondary to relationship between subcutaneous and total body fat
  • there is a relationship between SSF and Db
  • age is independent predictor for both men and women
18
Q

Using Skinfold Method

A
  • jackson et al. used quadratic model to develop widely applicable generalized equations: 18-60 years up to 45% bodyfat
  • these equations also account for impact of age on fat
  • advantage is ability to use one equation rather than many to accurately measure clients’ %BF
  • most equations use at least 2 or 3 skinfold sites
  • equation should use both upper and lower sites
  • nomograms allow one to save time but have limitations
  • takes a great deal of time and practice to develop skill with SSF
  • following standardized procedures greatly improves accuracy and reliability of measures
19
Q

Standardized Procedures for Skinfold Measurments ±

A
  • take all measurements on right side of body
  • carefully identify, measure, and mark the site
  • grasp site firmly between thumb and index finger of left hand
  • lift fold 1 cm above site to be measured
  • lift fold on line perpendicular to long axis of skinfold
  • need to separate the thumb and index finger for clients with extremely large skinfolds
  • keep fold elevated while you take the measurement
  • place jaws of caliper perpendicular to fold, approximately 1 cm below thumb and index finger
  • release jaw pressure slowly
  • take measurement 4 sec after pressure is released
  • open caliper jaws and remove from site
  • close jaws slowly to prevent damage or loss of calibration
20
Q

Recommendations for Skinfold Technicians

A
  • be meticulous when locating the anatomical landmarks and skinfold sites
  • read caliper dial to nearest available measure
  • take a minimum of 2 measures per site
  • take additional measures if values vary ±10%
  • take measurements in rotational order rather than consecutively at each site
  • dry and lotion free skin
  • do not take measures immediately following exercise
  • practice taking SSF on 50-100 clients
  • use metal calipers when possible
  • train with skilled technicians and compare your results
  • seek additional training at continuing ed courses
21
Q

Sources of Measurement Error for SSF

A
  • differences between technicians
  • failure to use standardized skinfold sites
  • poor intra-tester reliability or consistency
  • lesser measurement consistency of plastic calipers
  • hydration level of client
  • deviation from right side only measurement
  • attempting to measure %BF of extremity of extremely obese clients
22
Q

Bioelectrical Impedance Method

A
  • rapid, noninvasive, and relatively inexpensive method
  • low-level current is passed through body
  • impedance or resistance to flow is measured
  • impedance is greater as %BF increases
23
Q

Assumptions of BIA

A
  • human body is shaped like a perfect cylinder with uniform length and cross-sectional area
  • impedance to current flow is directly related to length of conductor and inversely related to cross-sectional area
  • as biological tissues act as conductors or insulators, current flow follows path of least resistance thru body
  • impedance is a function of resistance and opposition to current flow caused by cell membrane
24
Q

Using BIA

A
  • BIA prediction equations are either population-specific or generalized
  • experts recommend using BIA estimates with caution unless certain which equations are used in device
  • relative predictive accuracy of BIA is similar to SSF
25
Q

Advantages of BIA

A
  • requires little technical skill
  • generally more comfortable than SSF
  • intrudes less upon client’s privacy
  • can be used to estimate %BF of obese individuals
  • less expensive units have been recently marketed for home use
26
Q

BIA Client Guidelines

A
  • client should not eat/drink within 4 hours of test
  • client should not exercise vigorously within 12 hr of test
  • client should void within 30 min of test
  • client should abstain from alcohol within 48 hr of test
  • client should ingest no diuretics prior to test including caffeine unless prescribed by physician
  • postpone testing female clients who perceive they are retaining water
27
Q

Other Methods

A
  • relatively simple, inexpensive, require lesser skill or training
  • waist-to-hip circumference ratio
  • near-infrared interactance method
  • body mass index
28
Q

Putting It All In Perspective

A
  • exact %BF for optimal health risk yet to be determined: males 13% females 28% (averages for 18-34 yo)
  • ranges considered satisfactory for health: males 10-22% females 20-32%