week 3: body comp Flashcards
what is body comp
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)
why is body comp used
an outcome measure to determine the effectiveness of community-based obesity prevention strategies
body comp norms
accepted norms do not exist
reference values based on skin fold percentiles:
- 12-23% for males
- 17-26% for females
why do we measure body comp
- risk of metabolic diseases (CVD, peripheral vascular disease, hypertension, T2D, metabolic syndrome, dyslipidemia, stroke)
- maximize performance/health
two-component body comp model
- anthropometry (circumference measures)
- skinfold thickness
- bioelectrical impedance analysis
- underwater weighing
- plethysmography (bodpod)
- ultrasound
three-component body comp model
- dual-energy x-ray absorptiometry (DEXA)
- MRI
- CT
relationship between % body fat and CVD risk factors
- 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
DEXA
- 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
UWW (underwater weighing)
most valid methods
- densitometry - fat and lean tissues have different densities
air-displacement plethysmography
bod pod
densitometry technique
- displacement of air in a sealed compartment
BMI
- 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
BMI equation
BMI = Wt (kg) / Ht^2(m^2)
BMI norms
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
BMI strengths
- simple, inexpensive, reliable measure
- national and international standards are available
- high specificity for detecting excessive adiposity with higher BMI values in adults
BMI weakness
- does not provide direct body fat measures
- poor estimates of bod fat in some ethnic groups, ages, body build/frame size
waist circumference
proxy method for intra-abdominal fat
waist circumference method
- 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
waist circumference strengths
- 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
waist circumference weakness
- does not directly measure intra-abdominal fat
- practitioner must be trained
- 2-3 measures need to be taken and averages
skinfold thickness
- 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%
skinfold method
- 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
skinfold strengths
- 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
skinfold weakness
- calipers vary in quality, and some can be grossly inaccurate
- intra and inter-rater reliability
- not recommended for people with BMI> 30kg.m^2
skinfold measurement errors
- poor anatomical landmark identification
- poor measurement technique
- inexperienced evaluator
- extremely obese or lean participant
- improperly calibrated caliper
bioelectrical impedance analysis
- 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
Bioelectrical impedance analysis strengths
- validated equation available for adults and children
- standard error estimates available for BIA published equations
bioelectrical impedance analysis weakness
- 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)
