Scientific Basis of Body Composition Analysis

Question 1

Intro

Answer 1

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

Question 2

Role of Fat in Normal Physiology

Answer 2

• 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

Question 3

Body Composition and Clinical Analysis

Answer 3

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

Question 4

Associated Risks of Obesity

Answer 4

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

Question 5

Conditions Linked to Too Little Bodyfat

Answer 5

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

Question 6

Classification and Uses of Body Composition Measures

Answer 6

• 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

Question 7

Additional Uses for Body Composition Measures

Answer 7

• 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

Question 8

Body Composition Models

Answer 8

• 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

Question 9

Assumptions of 2 Component Model

Answer 9

• 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)

Question 10

Hydrostatic Weighing

Answer 10

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

Question 11

Guidelines for Hydrostatic Weighing

Answer 11

• 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

Question 12

Special Considerations for Hydrostatic Weighing

Answer 12

• 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

Question 13

Air Displacement Plethysmography

Answer 13

• 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

Question 14

Dual-Energy X-Ray Absorptiometry

Answer 14

• 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

Question 15

Filed Methods for Assessing Body Composition

Answer 15

• 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

Question 16

Skinfold Method

Answer 16

• 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

Question 17

Assumptions of SSF

Answer 17

• 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

Question 18

Using Skinfold Method

Answer 18

• 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

Question 19

Standardized Procedures for Skinfold Measurments ±

Answer 19

• 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

Question 20

Recommendations for Skinfold Technicians

Answer 20

• 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

Question 21

Sources of Measurement Error for SSF

Answer 21

• 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

Question 22

Bioelectrical Impedance Method

Answer 22

• 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

Question 23

Assumptions of BIA

Answer 23

• 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

Question 24

Using BIA

Answer 24

• 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

Question 25

Advantages of BIA

Answer 25

• 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

Question 26

BIA Client Guidelines

Answer 26

• 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

Question 27

Other Methods

Answer 27

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

Question 28

Putting It All In Perspective

Answer 28

• 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%