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
Height - Weight Tables
Body composition is a better indicator of fitness than body weight/height. 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.
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
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
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)
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
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
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
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
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
Disadvantages
Cost? Is it worth it? Few Age/Gender Specific Equations Accurate?
– Futrex 5000 3.1-4.2%– Futrex 5000A 6.3%– Futrex 1000 4.8-6.3%– Sum 3 2.4-3.6– BIA 5.0-7.1%
Skinfolds
Measurement of subcutaneous adipose tissue at specific anatomical sites
BD or %fat is obtained with the use of equations (either population specific or generalized)
SF Procedures
Take all measurements on the right side of the body
Identify and mark site Grasp skin and fat between thumb and
index finger 1cm above marked site Continue grasping at the site while
taking the measurement
SF Procedures
Take at least 2-3 non-consecutive measurements - if values vary by +2mm take additional measurements
No measurements directly after exercise
Equations
Jackson’s 3-site– Males - BD=1.10938-
0.0008267(sum3)+0.0000016(sum3)2-0.0002574(age)
– chest, abdomen, thigh– Females - BD=1.0994921-
0.0009929(sum3)+0.0000023(sum3)2-0.0001392(age)
– triceps, suprailiac, thigh
Waist to Hip Ratio
Indication of the pattern of body fat distribution
Indicator of the health risks of obesity– excess trunk fat - increased risk of
hypertension, type 2 diabetes, high cholesterol, CAD, premature death
Measurements
Made with a tape measure Waist - at the level of the umbilicus Hips - biggest part of the gluteals
Waist to Hip Ratio
Risks increase with increasing ratios Men
– Very low risk <.95– Low risk .96-.99– High risk >1.00
Waist to Hip Ratio
Risks increase with increasing ratios Women
– Very low risk <.80– Low risk .81-.84– High risk >.85
Body Mass Index (BMI)
Ratio of a person’s weight (kg) to the height squared (m2)
Used to categorize people with respect to their degree of obesity
Not used to determine % fat Table 4.7 and Table 4.8
Calculations for Optimal BW
1. Determine % fat 2. Calculate Fat Weight
– BW * %fat ÷ 100 3. Calculate Fat-Free Weight
– BW - FW 4. Calculate Desirable Weight
– FFW ÷ (1- (desired %fat ÷ 100))
Calculations
5. Calculate amount of weight that needs to be lost– BW - Desirable Weight
6. Calculate kcal deficit– 3500 kcal per pound of weight needed to be lost
7. Assuming loss of 1 pound (3500 kcals) per week, calculate # weeks to reach goal
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