Categorizing the human body
- Body size
- Body structure
- Body composition
Body size
- Volume
- Mass
- Length
Body structure
- Distribution of arrangement
- Skeleton, muscle, fat
Body composition
- Amount of each constituent (e.g. muscle & fat)
Body composition model
- Two components
- Three components
- Four components
Two components
- Fat free mass or lean body mass + fat mass = body mass
Three components
- Total body water + fat free dry mass + far mass = body mass
- FFDM - protein, glycogen and mineral in bone and soft tissue
Four components
- Total body water + bone mass + residual + fat mass = body mass
Understanding Body composition models
Direct assessment
- Analysis of cadaver
Indirect assessment
- Body mass index
- Hydrostatic weighing
- Bod pod
- Dual-energy x-ray absorptiometry
- Computer tomography
- Magnetic resonance imaging
- Skinfold and girth measurements
- Surface anthropometry
- Bioelectrical impedance analysis
Body fat
- Essential
- Storage
Essential - Nerve tissue - Bone marrow - Organs (membranes) If we loose this we compromise health and physiological function
Storage
- Energy reserve
- Accumulates when excess energy is ingested
- Decline when less energy is ingested then expended
Female and male reference
Females
- Total: 27.0%
- Storage: 15%
- Essential: 12.0%
Males
- Total: 15.0%
- Storage: 12.0%
- Essential: 3.0%
Increases with age
% body fat and fat mass
- Cultural
- Genetics
- Non-transmissible
Culture
- 30%
Genetics
- 25%
Non-transmissible
- 45%
Specific health risk
- Hypertension
- Stroke
- Renal disease
- Sleep apnoea
- Osteoporosis
- Cancer – endometrial, breast, colon
- Elevated plasma lipids
- Gallbladder disease
- Mensural irregularities
Fat mass and performance
- Force and mass
- Acceleration
- Metabolic cost
Force and mass
- Increases mass without increasing the ability to produce force will result in reductions in performance
Acceleration
- Directly proportional to force but inversely proportional to mass
Metabolic cost
- Increases the metabolic cost of physical activities that require movement of body mass
Athletes and body composition
Body composition is commonly used in three ways:
- Monitor effectiveness of training program or dietary regime
- Estimate optimal body weight or competition weight
- Screen and monitor health status
Body mass index
- Equation
- Limitation
Body mass index = body mass (kg)/ (height (m))2
Limitation
- Does not take into account the distribution of the different constituents in the body
Waist circumference & waist-to-hip ratio
Equation
- Waist size/ Hip size
- Higher ratio, higher risk of heart disease and other obesity related disorders
- Better predictor of mortality in the elderly then BMI. WHY? - fat distribution
- Waist circumference good indicator of CVD risk factors, body fat distribution and hypertension in type 2 diabetes
Densitometry
- Components within the body - Density equation
- Archimedes principle
- Hydrostatic weighing
- Developed to distinguish components within the body
- CHO: <1% of body mass
- Minerals: ~4%
- Fat: ~ 25%
- Protein: ~ 20%
- Water: ~ 60%
+ Different densities
Density = mass/volume
Archimedes principle
- Same mass but different volumes
- Relationship between buoyancy and displaced liquid
- Gold crown example - submerged weight and amount of water displaced can determine density
Hydrostatic weighing
- Submerging an individual in H2O
- Measured weight pre and during submersion
Siri equations
- % body fat = (495/body density) - 450
Limitations
- Calculations based off the two compartment model (fat mass and fat free mass)
- Body comp changes after weight training
- In a muscular person the Siri equation will over estimate body fat and underestimate fat free mass
Hydrostatic Weighing
- Performed after maximal exhale
- Reduce air remaining in the lungs
- Even after maximal exhale there is some air remaining in the lungs
- Residual lung volume must be measured and corrected for
- Otherwise body density will be underestimated
- Must also avoid carbonated beverages in the hrs before testing
Air displacement Plethysmography
- Body pod
- Measures whole-body volume through air displacement
- Good reliability
- Accurate
- 3-5 mins
- Lower body fat % compared to hydrostatic weighing and DXA
How it works:
- Weighed outside bod pod
- Sits in the 750 L bod pod
- Persons volume = original volume in the chamber - the air that has been displaced
- Pulmonary gas volume is assessed
- True volume (pulmonary gas volume - persons measured volume)
- Body density
Skinfold technique
- Most frequently used
- Estimates body fat through the thickness of the skinfold
4 most common sites (triceps, abdominal, subscapular, biceps)
- Body fat % is calculated from the sum of 4, 7 or 10 sites
Girth measurements
- Usefulness of girth scores
- Helps rank individuals
- Practical value –clothing
- Body fat predictions from girths
- Rehabilitation
Bioelectrical impedance analysis
Based on the principle that different tissues have difference impedance (resistance) to an electrical current (most reliable)
- Electrodes are places on different parts of the body (often the hand and foot)
- Current applied at one can be measures at the other
- The less the measured resistance the higher the body water composition
- Adipose tissue has a high resistance or impedance where as muscle – which is 75% water – has a low resistance
- Can be used to estimate body fat %, lean body mass % and percentage of water
Duel energy x-ray absorptiometry (DXA)
- Clinical standard for measuring bone density
- Based on the absorption of x-rays
- 2 different intensity x-ray pass over the body
- Loss of signal at various points in record
- Underestimates body fat compared to underwater weighing
- Test conditions must be standardized
Computer tomography (CT)
Uses ionizing radiation by x-ray beam to create images of body segments
Provides the following information:
- Total tissue area
- Thickness and volume of tissue within an organ
- Fat surrounding a tissue and fat within a tissue
Magnetic resonance imaging (MRI)
- Results are similar to those obtained by CT
- Uses electromagnetic radiation
- Magnetic fields and radio waves
- Passing these strong waves through the body affects atoms within the body
- All tissues within our body contain water which contain hydrogen atoms and they play a large role in the image that appears
- Structures with more hydrogen atoms appear brighter than those with a low portion this is why fatty tissue appears much brighter then bone
