Understanding Body Composition Assessment

• Body composition refers to the ratio of physiological constituents in relation to each other or the whole.
• Body fat percentage (BF) calculation: BF = (Fat Mass/Body Mass) x 100

Compartment Models

• Compartment models quantify components of the body to provide insight into its composition.
• Validity is generally greater when more compartments are assessed.
• The number of compartments assessed doesn't influence reliability.

Categories of Assessment

• Direct: body compartment volume is directly measured
• Indirect: body compartment volumes are estimated with assumptions and established relationships involving tissue/material characteristics.
• Doubly Indirect: estimation equations are used to predict the volume of body compartments without direct measurement.

Methods of Assessment

• BMI (Body Mass Index).
• Waist-Hip Ratio.
• Skinfolds.
• Bioelectrical Impedance Analysis.
• Air displacement plethysmography.
• Dual x-ray absorptiometry.
• Magnetic resonance imaging.
• Hydrostatic weighing.

Direct Methods

• Cadaver Dissection: directly quantifies the volume of fat and fat-free mass in a deceased reference cadaver, but is rarely performed with limited diversity.
• Difficult to make statistical inferences and conduct indirect assessment validation studies

Indirect Methods

• Dual-Energy X-Ray Absorptiometry (DEXA/DXA): Uses two low-dose x-ray beams to differentiate between tissues:
• Bone, muscle, and fat absorb varying amounts of electromagnetic radiation at different rates.
• This method determines the quantity and location of fat and fat-free mass (whole body & segmental).
  • Constant hydration status of fat and fat-free mass assumed.
  • Hydration status can affect radiaition of absorption
• Hydrostatic Densitometry (Underwater Weighing - UWW).
  • Relies on Archimedes Principle.
  • Calculation – Density = Body Mass in Air / Body Volume
  • Assumes constant density of fat and fat-free mass and the subject exhales all air possible from lungs
• Air Displacement Plethysmography (BOD POD):
  • Relies on Archimedes principle.
  • Measures pressure differential to determine displaced air volume, body density calculated by dividing body mass by volume, assumes constant density of fat and fat-free mass

Doubly Indirect Methods

• Bioelectrical Impedance Analysis: Estimates body fatness and fat-free mass based on body resistance and reactance.
  • Resistance to current flow depends on conductance.
  • Fat-free mass is hydrated, meaning greater conductance.
  • Resistance is impacted by distance.
• Skin-Fold Assessments:
  • Calibrated calipers measures skin and subcutaneous fat thickness
  • Skin+subcutaneous fat measures estimate whole body
• Estimates total body fatness from subcutaneous measures
• Does not provide insight into location of body fat
• Standard Assessments use 3 - 7 measurement sites
• Subject to considerable Measurement Error

Anthropometrics

• Body Mass Index (BMI): Body mass (kg) relative to height (m) (BMI = kg/m²)
  • Not a compartment-based body composition assessment method.
  • Measures of body proportions which estimate body composition
  • Overestimates fatness in shorter people, underestimates in taller people
  • Tendency to overestimate fatness in lean and athletic individuals
• Waist-to-Hip Ratio: Ratio of waist to hip circumference (cm) (WHR = cm/cm)
  • Not a compartment-based body composition assessment method.
  • Accounts for age and sex-based difference

Benefits and Drawbacks of Body Composition Methods

• Body Mass Index (BMI): Free, fast, predictor of life expectancy but does not give a precise assessment of percentage of body fat for athletes.
• Skinfold Thickness Measurements: Convenient, fast, portable, useful for detecting changes in percentage of body fat but requires precise, consistent technique and is not accurate for very thin or very fat people.
• Waist-Hip Ratio (WHR): Fast and free with tape measure does not provide information on body fat.
• Bioelectrical Impedance Analysis (BIA): Inexpensive, portable, fast, accurate for estimating total body water in populations but accuracy in detecting changes in percentage of body fat is poor.
• Underwater Weighing (UWW): Relatively accurate and consistent for measuring changes in percentage of body fat but is expensive and hard to find.
• Dual-Energy X-Ray Absorptiometry (DXA): Most accurate for information on total and regional percentage of fat, most precise, but not portable.

The Science of Weight Management

• Energy Balance Model (EBM):.
  • Describes relationship between energy intake and energy expenditure.
  • Weight change = total energy intake - total energy expenditure
  • When energy intake and output are unbalanced, weight changes will occur.

Factors Regulating Weight Management

• Environment and Lifestyle (cognition, reward, choice, mood and stress).
• Brain.
• Energy Intake.
• Energy Expenditure.
• Individual "Wiring" - Genetic & early life events
• Hormonal control of appetite

The Fidget Factor Hypothesis

• Neurological regulated movements contribute to energy expenditure with the belief that it occurs at random, but it is linked to caloric intake.

Average Body Composition Characteristics

• In absolute terms, body composition varies dramatically based on sex and age; however, relative to body mass at any age, body composition and distribution are relatively similar between sexes.
• Males generally have greater total muscle mass owing to greater upper body muscle.
• Females generally have greater essential fat

Relationships Between Body Composition and Athletic Performance

• Volleyball: BF% negatively correlated with vertical (r = -0.28, p < 0.05) and horizontal jump performance (r = -0.48, p < 0.001)
• Youth Soccer (12-15): BF% is correlated with t-drill (r = 0.61), PACER (r = -0.62), and Vertical jump (r = -0.57) (all p < 0.01). FFM is correlated with t-drill (r = -0.43, p < 0.01).
• Recreationally Trained College Students: LBM positively correlates (r = 0.38) with absolute values of VO2max