Scientific Basis of Body Composition Analysis Flashcards
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%
