week 3: body comp

Question 1

what is body comp

Answer 1

refers to the components that make up the body
- body weight and relative amounts of muscle, fat, bone and other vital issues
- often limited to fat and lean body mass (fat-free mass) - expressed as relative (%) and absolute (kg)

Question 2

why is body comp used

Answer 2

an outcome measure to determine the effectiveness of community-based obesity prevention strategies

Question 3

body comp norms

Answer 3

accepted norms do not exist
reference values based on skin fold percentiles:
- 12-23% for males
- 17-26% for females

Question 4

why do we measure body comp

Answer 4

• risk of metabolic diseases (CVD, peripheral vascular disease, hypertension, T2D, metabolic syndrome, dyslipidemia, stroke)
• maximize performance/health

Question 5

two-component body comp model

Answer 5

• anthropometry (circumference measures)
• skinfold thickness
• bioelectrical impedance analysis
• underwater weighing
• plethysmography (bodpod)
• ultrasound

Question 6

three-component body comp model

Answer 6

• dual-energy x-ray absorptiometry (DEXA)
• MRI
• CT

Question 7

relationship between % body fat and CVD risk factors

Answer 7

• men with a normal BMI and high BF% had a 63% increased risk of having one or more cardiovascular risk factors
• women with a normal BMI and high BF% had a 56% increased risk of having one or more cardiovascular risk factors

Question 8

DEXA

Answer 8

• considered the gold-standard
• provides estimate of bone, fat, and lean tissue densities
• expensive equipment that is usually found in research and clinical settings
• full body x-ray

Question 9

UWW (underwater weighing)

Answer 9

most valid methods
- densitometry - fat and lean tissues have different densities

Question 10

air-displacement plethysmography

Answer 10

bod pod
densitometry technique
- displacement of air in a sealed compartment

Question 11

BMI

Answer 11

• proxy measure for body fat
• simple and reliable measure commonly used in clinical situations and epidemiological research
• used to classify underweight, normal, overweight and obesity classes in adults and children

Question 12

BMI equation

Answer 12

BMI = Wt (kg) / Ht^2(m^2)

Question 13

BMI norms

Answer 13

underweight: <18.5
normal: 18.5-24.9
overweight: 25-29.9
class 1 obesity: 30-34.9
class 2 obesity: 35-39.9
class 3 obesity: >40

Question 14

BMI strengths

Answer 14

• simple, inexpensive, reliable measure
• national and international standards are available
• high specificity for detecting excessive adiposity with higher BMI values in adults

Question 15

BMI weakness

Answer 15

• does not provide direct body fat measures
• poor estimates of bod fat in some ethnic groups, ages, body build/frame size

Question 16

waist circumference

Answer 16

proxy method for intra-abdominal fat

Question 17

waist circumference method

Answer 17

• measurement at the midpoint between the lower margin of the last palpable rib and the top of the iliac crest
• tape should be snug around the body and parallel to the floor
• participants should stand with arms at the sides; feet positioned close together, weight evenly distributed
• relaxed position

Question 18

waist circumference strengths

Answer 18

• WC is closely linked to increased risk from chronic disease in both adults and children
• may provide a better indicator of chronic disease risk than BMI, especially in individuals with normal BMI values

Question 19

waist circumference weakness

Answer 19

• does not directly measure intra-abdominal fat
• practitioner must be trained
• 2-3 measures need to be taken and averages

Question 20

skinfold thickness

Answer 20

• estimation of body fat
• most widely used field technique
• rationale = age-dependent proportion of body fat is deposited subcutaneously
• the amount of adipose tissue that can be pinched provides some indication of the amount of overall body fat
• estimation of percent body fat from skinfold measures that has error approx. 3.5%

Question 21

skinfold method

Answer 21

• using skinfold calipers, all measurements are taken on the right side of the body
• carefully landmark and measure skinfold sites
• generalized body density formulas using 3-7 measurement sites
• body comp is estimated from the siri equation
  %BF=(4.95/density)-4.5

Question 22

skinfold strengths

Answer 22

• relatively easy measurement with minimal equipment
• the relationship between subcutaneous fat and total body fat varies with race, age and sex. Therefore, population specific equations have been developed

Question 23

skinfold weakness

Answer 23

• calipers vary in quality, and some can be grossly inaccurate
• intra and inter-rater reliability
• not recommended for people with BMI> 30kg.m^2

Question 24

skinfold measurement errors

Answer 24

• poor anatomical landmark identification
• poor measurement technique
• inexperienced evaluator
• extremely obese or lean participant
• improperly calibrated caliper

Question 25

bioelectrical impedance analysis

Answer 25

• estimates fat-free mass and total body water
• bodys ability to conduct a mild electrical current to indirectly measure body fat
• impedance: opposition to the flow of current where electrolytes in body water conduct electrical current

Question 26

Bioelectrical impedance analysis strengths

Answer 26

• validated equation available for adults and children
• standard error estimates available for BIA published equations

Question 27

bioelectrical impedance analysis weakness

Answer 27

• equations less valid for identifying adiposity in individuals with high or low BMI values
• accuracy depends on following standardized procedures (normal hydration, fasting, and avoiding exercise)