3LO3 - BODY COMPOSITION

body composition considerations

• sex and aging effects

• body fat distribution (apple vs pear)

• waist to hip ratio

• body image and eating disorders

• scales vs other signs of progress

• different types of fat and their roles

aging and body composition

• increased fat mass with age (after ~30)

• decreased muscle mass with age

sex differences in fat distribution

• males: more abdominal fat

• females: more even distribution or below waist

apple vs pear fat distribution

• apple: abdominal fat, higher health risk

• pear: fat stored below waist, lower risk

direct (gold standard) body composition methods

• mri

• ct

• dxa

mri body composition assessment

• strong magnetic field realigns hydrogen protons

• energy released differs by tissue type

• radio waves read ion patterns

• reconstructs 3d image

• accurate but expensive and inaccessible

• not whole body

ct body composition assessment

• uses rotating x-rays and detectors

• reconstructs 3d image

• best for visceral adipose tissue

• accurate but expensive

• radiation exposure → not recommended

dxa body composition assessment

• low-dose x-rays with two energy peaks

• distinguishes bone, fat, lean tissue

• accounts for bone mineral variability

• estimates bone mineral, fat, lean mass

indirect lab-based body composition methods

• hydrostatic weighing

• bodpod

hydrostatic weighing principle

• weight loss underwater proportional to water displaced

• used to estimate body volume

hydrostatic weighing corrections

• residual lung volume

• gastrointestinal volume (~100 ml)

bv = ((bm − net uww) / density of water) − (rv + gv)

• bv: body volume

• bm: body mass

• net uww: net underwater weight

• rv: residual lung volume

• gv: gastrointestinal volume

hydrostatic weighing limitations

• inaccurate rv estimation

• trapped air (lungs, suit, hair)

• incomplete exhalation

• temperature variability

bodpod principle

• air displacement plethysmography

• pressure–volume relationship (p1/p2 = v2/v1)

bodpod considerations

• hair

• thoracic gas volume

• body surface area

bodpod system

• two chambers

• diaphragm creates pressure oscillations

• body volume from difference with and without client

field-based body composition methods

• skinfolds

• bia

• bmi

• waist circumference

skinfold assessment

• measures subcutaneous fat thickness

• multiple sites used

• prediction equations estimate body density

skinfold assumptions

• skf reflects subcutaneous fat

• fat distribution similar within sex

• sum of skf relates to body density

skinfold limitations

• requires skilled qep

• uncomfortable for client

• not recommended if bmi > 30

• not recommended when wc is high

high waist circumference cutoffs

• males: >102 cm

• females: >88 cm

bioelectrical impedance analysis (bia)

• low-level electrical current

• estimates total body water

• measures resistance and reactance

bia physiological basis

• fat-free tissue has more water

• lower resistance = lower % body fat

bia limitations

hydration status affects accuracy

resistance vs reactance (bia)

• resistance: opposition to current flow

• reactance: opposition from cell membrane capacitance

• resistance is better predictor of ffm

bmi definition

body mass divided by height squared

bmi uses

• classify underweight, overweight, obese

• identify risk for obesity-related disease

bmi limitations

• does not reflect body composition

• affected by age, ethnicity, frame size

waist circumference significance

• reflects visceral (abdominal) fat

• stronger predictor of health risk than total body fat

health risks of high waist circumference

• hypertension

• type 2 diabetes

• dyslipidemia

• metabolic syndrome

two-component body composition model

• fat mass

• fat-free mass

• uses body density to estimate % body fat

body volume measurement methods

• hydrostatic weighing

• bodpod

body density equation

• db = bm / bv

• db: body density

• bm: body mass

• bv: body volume