Slide 5 - Hydrostatic Flashcards
What Densitometry measure
Measurement of body density
Db = body mass/body volume
How is body volume measured
Hydrodensitometry
Air displacement
What is hydrodensitometry
What do we measure air displacement with
Underwater weighing
BodPod
How is % body fat calculated using these methods
Calculated from Db using equations
Hydropdensitometry has been used for
It measures
What is the principle based off
Decades in fitness facilities and research
mass per unit volume of persons body
Archimedes principle
What is archimedes principle
The buoyant force is equal to the weight of the displaced water
Loss of weight under water is directly proportional to the volume and weight of the water displaced by the body
Volume of an object submerged in water equals
The volume of water displaced by the object
The loss of weight under water is directly proportional to
The volume and weight of the water displaced by the body
Object submerged in water is acted on by
That is equal to
A buuoyancy force
The weight of water displaced by the object
Mass displaced =
Weight (air) - Weight(water)
Volume =
2 equations
Loss of weight in water / density of water
Or
Weight (air) - weight (water) / density of water
Db =
Total body weight in AIR / volume
When does the forumla work
What do we therefore have to additional corrections
When the object has no hollow spaces
Lungs and other trapped air spaces in body
What is residual lung volume
Air trapped in lungs after maximal expiration
Can we directly measure residual volume
NO
Can estimate based on sex, height and age
Or on % of vital capacity
How much approx is residual volume
What is the deviation in % body fat when using ESTIMATED RV
1 - 2 litres
1 - 4%
Is gastrointestinal gas larger or smaller than RV
What is it assumed to be
Smaller amount
100ml
How do you control gastrointestinal gas
With pre test diet
Avoid gas producing food or soda
What is the additional correction for working out:
Db =
Body weight in air
______________
((Weight in air - weight in water) / Density) - (RV + 0.1L)
What are the assumptions made when doing hydrodensitometry
Separate densities of body compnents are additive
Densities of components are relatively constant from person to person
e.g. Density of fat = 0.9007 and FFM = 1.1000
Two component model:
Proportions of components in FFM are relatively constant from person to person
e.g. 73.8% water, 6.8% mineral, 19.4% protein
What is the validity of hydrostatic weighing
Chemically determined body density agrees within 0.6% with Db
What are the sources of error in hyrdrostatic weighing
Getting an accurate underwater weight
Value used for density of FFDb
Residual volume estimated
Hydrodensitometry is based on what principle
Archimedes
Body density is calculated by total body weight in air divided by body volume
True
Residual lung volume is approximately 0.1L
False
To correctly calculate the body volume, both the amount of water that is displaced and the density of water should be considered
True
Hydrodensitometry follows a 3 component model assuming that the proportions of components in fat free mass are relatively constant from person to person
False
A 30 year old women with body weight of 68 kg and height of 5’5’’ went through hydrostatic weighting assessment. The water temperature in the tank was 32 degree Celsius. What is the density of water
0.9951
A 30 year old women with body weight of 68 kg and height of 5’5’’ went through hydrostatic weighting assessment. The water temperature in the tank was 32 degree Celsius. What is the estimated residual volume
1.467
A 30 year old women with body weight of 68 kg and height of 5’5’’ went through hydrostatic weighting assessment. The water temperature in the tank was 32 degree Celsius. The density of water is 0.9951. What is her body density if her underwater weight was 1.0 and what is her % body fat
1.03589
28%
A 30 year old women with body weight of 68 kg and height of 5’5’’ went through hydrostatic weighting assessment. The water temperature in the tank was 32 degree Celsius. Her % body fat was 28%. She wants to go through exercise training and lose weight. What is her desired body weight if she wants 20% body fat assuming that she wants to keep same amount of lean body mass
61.2kg
A 30 year old women with body weight of 68 kg and height of 5’5’’ went through hydrostatic weighting assessment. The water temperature in the tank was 32 degree Celsius. She wants to go through exercise training and lose weight. Her desired body weight is 61.2kg. How much does she need to lose weight
6.8 kg
One of the assumptions of hydrostatic weighing method for body composition assessment is that densities of components are relatively constant from person to person
True
If underwater weight is measured higher that what it is, body density will be calculated higher and % body fat will be estimated higher
False
If you are a trained (strength and resistance-based exercise training) individual, using Siri equation after hydrostatic weighing method to estimate % body fat may result higher value
True
To evaluate _______ of the test, you will have another person measure on the same client
Objectivity
What describes the amount air trapped in lungs after a maximal expiration
Residual volume
The assumed amount of gas trapped in the gastrointestinal system when you use hydrostatic weighing method to assess body composition is approximately
0.1L
Which method will you report the best represent your body composition
DXA
Is hydrostatic weighing a more valid method than the skinfolds method.
True
How do you calculate desired body weight using LBM
Actual LBM / desired % LBM
How do you calculate RV for male and female
Male = 0.033 (ht inch) + 0.022(age) - 1.232
Female = 0.046 (ht inch) + 0.016(age) - 2.003
How do you work out FM
Body fat % x BW
How do you work out LBM
BW - FM
What is the equation for SIRI
What is the equation for Brozek
((4.950 / body density) - 4.5) x 100
((4.570 / body density) - 4.142) x 100
