Body Composition Assessment A description of assessment methods.
Learning Objectives • Differentiate among body build, body size, and body composition. • Discover how densitometry and several field techniques are used to assess body composition. • Find out what tissues of the body constitute fat-free mass
Learning Objectives • Calculate changes in FW and FFW with a weight loss program • Find out what guidelines best determine an subject's goal weight.
Body Composition • The relative % of body weight that is fat and fat-free tissue
Why measure body comp? • Health Implications • there is an ideal % fat for health reasons (prevent onset of diabetes, CHD, BP, etc…) • Make BW recommendations • can use % fat values to determine an ideal BW • how much fat to lose versus how much muscle to gain
Why measure body comp? • Describe Athletic Populations • swimmers are more fat (fat floats) • wrestlers/gymnasts want less fat • endurance runners don’t want massive amounts of muscle but power lifters do
Height - Weight Tables • Body composition is a better indicator of fitness than body weight/height. Being overfat (not necessarily overweight) has a negative impact on exercise/athletic performance. Standard height-weight tables do not provide accurate estimates of what you should weigh because they do not take into account the composition of the weight. A subject can be overweight according to these tables yet have very little body fat.
For example: • Body Builder: • 5’5” • 200 pounds • overweight according to height/weight tables • 4% body fat • ALL MUSCLE!!!
Fat Mass vs. Fat-free Mass • Two Component Model • Fat-free mass is composed of all of the body's nonfat tissue including bone, muscle, organs, and connective tissue. Fat mass includes all the body’s fat along with essential fat.
Assumptions of Two-Component Models • 1. The density of fat is 0.900 g/ml • 2. The density of FFM is 1.100 g/ml • 3. The densities of fat and FFM are the same for all individuals
Assumptions • 4. The densities of the various components of FFM are constant within an individual • 5. The individual being measured differs from a reference body (73.8% water, 19.4% protein, 6.8% mineral) only in the amount of fat
Fat Depots • 1. Subcutaneous • 2. Intermuscular • 3. Intramuscular • 4. Abdominal and Thoracic Cavity
Essential Fat • All fat is not bad!! • We need fat for padding of organs, insulation, energy source • There is a minimum amount that we need to function daily = essential fat • Gender specific • males ~ 3% • females ~ 7%
Essential Fat • Why the differences? • A male at 7% is like a female at 17% • Women are more complicated!! • Women have babies, menstrual cycles, etc… and need more fat for the survival of the species
Other Models • We can’t distinguish between fat that is essential and fat that is not so in order to have more components in a model: • we break the fat-free mass down further (referred to as a multi-component model) • ie., 3-component model (fat, water, solids) • ie., 4-component model (fat, water, mineral, protein)
Methods • 1. Under Water Weighing (Hydrodensitometry) • 2. Bioelectrical Impedance (BIA) • 3. Dual-Energy X-ray Absorptiometry (DEXA) • 4. Near-Infrared Interactance (NIR)
Methods • Anthropometric Measures (anthro=body; metric=measuresbody measurements) • 5. Skinfolds • 6. Circumference (WHR) • 7. Diameters (body typing) • 8. Height (BMI) • 9. Others…..??
Hydrodensitometry • Used to be considered the most accurate (up for debate now that DEXA is used) • +2.5% if done with experienced subjects • Considered a lab technique (can’t carry your tank with you out into the field) • Two-component Model
UWW • Fat Component - Fat (adipose)+Neural+Essential Fat • density of 0.9 g/ml • Fat-Free Component - muscle+bones+ tendons+organs • density of 1.10 g/ml
UWW • Water Density ~ 1.0 g/ml (temperature of the water affects the density) • Thus, if more fat will float (fat is less dense than water) • If more muscle will sink (muscle is more dense than water)
Hydrodensitometry • BD = BW/BV • Body weight = measured on a regular scale • Body volume = measured using hydrostatic (underwater) weighing accounting for water density and air trapped in lungs
UWW • Body Density = BW÷((BW-UWW)/H20 Density) - RV-0.1
UWW • Determine BV Calculate BD Calculate %fat • If have high BV low BD more fat • If low BV high BD less fat
UWW • Archimedes principle - an object (or human) immersed in fluid, loses an amount of weight equivalent to the weight of the fluid that is displaced • More simply - fill a bathtub with water - submerge - if catch all the water that spills over and weight it = BV
Procedures • 1. Wear light clothing (swimsuit) • 2. Use bathroom prior to weighing • 3. Calibrate scale • 4. Weight the chair or seat and equipment • 5. Measure water temp • 6. Remove all air from clothing
Procedures • 7. Sit in seat • 8. Submerge • 9. Blow all air out of lungs and remain still • 10. 3-10 trials; average of the highest three • 11. Subtract weight of apparatus from average UWW
Residual Volume • Cannot blow all of the air out of your lungs (that would be bad!!) • We need to account for the air that is left in the lungs (RV) + the air in the GI (~0.1L)
Determining RV • Prediction equations based on height and/or Vital Capacity • Male = 0.24 x VC • Female = 0.28 x VC • Male = 0.019(Ht cm)+0.0115(age)-2.24 • Female = 0.023(Ht cm)+0.021(age)-2.978 • Nitrogen Analysis (rebreathing apparatus)
Equations • Inaccuracies in hydrodensitometry are due to variation in the density of the fat-free mass from one individual to another. Age, sex, and race affect the density of fat-free mass. • Thus, we have age/gender/race/fat specific equations - Table 4-1 Guidelines
Equations • % fat = 4.57÷BD - 4.142 * 100 • ACSM guidelines: • %fat = 457÷BD - 414.2
Advantages • Accurate if done correctly • Many equations that are specific to each group
Disadvantages • Most subjects not comfortable blowing all their air out • especially hard for children to understand • methods to compensate for this • Ambulatory problems (ie., elderly) getting into a pool/tank • Some people just do not like water
Sources of Error • Not getting all air out • Reading scale wrong • Are not using the correct equation • Estimation of RV
BIA • Based on the premise that fat-free tissue is a better conductor of an electrical current (contains water and electrolytes) than fat tissue • The resistance to current flow is inversely related to FFM
Assumptions • 1. The human body is a perfect cylinder with uniform length and cross-sectional area • 2. The impedance to a current is directly related the length of the conductor and inversely related to its cross-sectional area
Assumptions • 3. Biological tissues act as conductors or insulators, and the flow will follow the path of least resistance • 4. Impedance is a function of resistance and reactance (opposition to flow caused by the capacitance of a cell membrane)
BIA • Abstain from eating or drinking for 4 hours prior • No exercise 12 hours prior • No alcohol 48 hours prior • No diuretics (caffeine) prior to assessment
Equations • Each machine has its own equation (developed by the manufacturer and is proprietary) • %fat = 4.57 ÷ (1.1411 - ((BW * Resistance) ÷ Ht2)) - 4.142 * 100 • ht = length of the conductor
BIA Reseach Equations • Population-specific equations have been developed through research • Used for children, different races, different ages etc… (p. 161) • May have better accuracy than machine equations
Advantages • Non-invasive • Safe • Easy to administer • Accurate on some populations • Field technique
Advantages • More costly than SF calipers • Many studies have begun to cross-validate (just because the equation worked on the researchers population doesn’t mean it will work on others) • Beginning to develop specific equations • get resistance value from machine and enter into a specific equation
Disadvantage • The accuracy has been questioned: • Skinfolds 2.4 % error • BIA 5% error • Visual 3.1% error • Race cannot be entered into the machine • Children distribute water differently than adults
DEXA • 3 component model • bone, fat, fat-free mass • assesses total bone mineral content • usually found in a clinical setting
Advantages • Accurate • Measurement of bone content (osteoporosis) • safe • rapid • minimal subject cooperation (just lay there)
Disadvantage • Costly • Limited Access
NIR • Based on the premise that the degree of infrared light absorption is related to the composition of the substance through which light passes • Fat and Fat-Free Mass absorb and reflect light differently
NIR • Emit infrared light at wavelengths of 940-950 nm into a body part (ie., biceps) and measures the intensity of the re-emitted light • More specific equations/machines are necessary
Advantages • Non-invasive • Safe • Easy to administer • Field technique