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Hydrostatic weighing, also referred to as underwater weighing, hydrostatic body composition analysis and hydrodensitometry, is a technique for measuring the density of a living person's body. It is a direct application of Archimedes' principle, that an object displaces its own volume of water.

Method

The procedure, pioneered by Behnke, Feen and Welham as means to later quantify the relation between specific gravity and the fat content,^[1] is based on Archimedes' principle, which states that: The buoyant force which water exerts on an immersed object is equal to the weight of water that the object displaces.

Example 1: If a block of solid stone weighs 3 kilograms on dry land and 2 kilogram when immersed in a tub of water, then it has displaced 1 kilogram of water. Since 1 liter of water weighs 1 kilogram (at 4 °C), it follows that the volume of the block is 1 liter and the density (mass/volume) of the stone is 3 kilograms/liter.

Example 2: Consider a larger block of the same stone material as in Example 1 but with a 1-liter cavity inside of the same amount of stone. The block would still weigh 3 kilograms on dry land (ignoring the weight of air in the cavity) but it would now displace 2 liters of water so its immersed weight would be only 1 kilogram (at 4 °C).

In either of the examples above, the correct density can be calculated by the following equation:^[2]

D_{b}={\frac {M_{a}}{{\frac {M_{a}-M_{w}}{D_{w}}}-RV}}

Where:

$D b$ = Density of the body;
$M a$ = "Mass in air" (i.e. dry weight);
$M w$ = "Mass in water" (i.e. underwater weight);
$D w$ = Density of water (based on water temperature);
$RV$ = Residual volume (the unfilled space enclosed by the body- e.g. volume of air in the lungs + respiratory passages after a maximum exhalation).

The residual volume in the lungs can add error if not measured directly or estimated accurately. Residual volume can be measured by gas dilution procedures or estimated from a person's age and height:^[3]

RV-Est(liters, Men) = 1.310 × Ht. (meters) + 0.022 × Age (yrs., take as 25 for 18-25) − 1.232
RV-Est(liters, Women) = 1.812 × Ht. (meters) + 0.016 × Age (yrs., take as 25 for 18-25) − 2.003

These estimates are for adults aged 18-70, have standard deviation of about 0.4 litres and have dependence on ethnicity, environmental factors, etc.^[4] Residual volume may also be estimated as a proportion of vital capacity (0.24 for men and 0.28 for women).^[5]

Application

Once body density has been calculated from the data obtained by hydrostatic/underwater weighing, body composition can be estimated. The most commonly used equations for estimating the percent of body fat from density are those of Siri^[6] and Brozek et al.:^[7]

Siri (1956): Fat % = [4.950 /Density - 4.500]×100

Brozek et al. (1963): Fat % = [4.570 /Density - 4.142]×100

References

^ Behnke AR; Feen BG; Welham WC (1942). "The Specific Gravity of Healthy Men". JAMA (Reprinted in Obesity Research). 118 (3): 495–498. doi:10.1002/j.1550-8528.1995.tb00152.x. PMID 7627779.
^ McArdle, William D; Katch, Frank I; Katch, Victor L (2010). Exercise Physiology: Energy, Nutrition, and Human Performance (7th ed.). Lippincott Williams & Wilkins. p. 741. ISBN 978-0-7817-4990-9.
^ Quanjer P.H., Ed. (1983). "Standardized Lung Function Testing". Bulletin Européen de Physiopathologie Respiratoire. 19 (suppl. 5). European Community for Coal and Steel, Luxembourg: 1–95.
^ Ph.H Quanjer; G.J. Tammeling; J.E. Cotes; O.F. Pedersen; R. Peslin; J-C. Yernault (1993). "Lung volumes and forced ventilatory flows". European Respiratory Journal. 6 (suppl. 16): 5–40. doi:10.1183/09041950.005s1693.
^ Wilmore, J. H. (1969). "The use of actual predicted and constant residual volumes in the assessment of body composition by underwater weighing". Med Sci Sports. 1 (2): 87–90. doi:10.1249/00005768-196906000-00006.
^ Siri, SE (1961), "Body composition from fluid spaces and density: analysis of methods", in Brozek J, Henschel A (eds.), Techniques for measuring body composition, Washington, DC: National Academy of Sciences, National Research Council, pp. 223–34
^ Brozek J, Grande F, Anderson JT, Keys A (September 1963), "Densitometric Analysis of Body Composition: Revision of some Quantitative Assumptions", Ann. N. Y. Acad. Sci., 110 (1): 113–40, Bibcode:1963NYASA.110..113B, doi:10.1111/j.1749-6632.1963.tb17079.x, PMID 14062375, S2CID 2191337

@@ Line 1: / Line 1: @@
+{{Short description|Technique for measuring the density of a living person's body}}
-{{refimprove|date=June 2011}}
-'''Hydrostatic weighing''', also referred to as "underwater weighing," "hydrostatic body composition analysis," and "hydrodensitometry," is a technique for measuring the [[density|mass per unit volume]] of a living person's body. It is a direct application of  [[Archimedes' principle]], that an object displaces its own volume of water. It is also a method of making babies the easy way.you usually put crabs in it and your instructor tells you to ignore them and just do the test normally.
+'''Hydrostatic weighing''', also referred to as '''underwater weighing''', '''hydrostatic body composition analysis''' and '''hydrodensitometry''', is a technique for measuring the [[density]] of a living person's body. It is a direct application of  [[Archimedes' principle]], that an object displaces its own volume of water.
 ==Method==
+The procedure, pioneered by [[Albert R. Behnke|Behnke]], Feen and Welham as means to later quantify the relation between specific gravity and the fat content,<ref>{{cite journal | doi = 10.1002/j.1550-8528.1995.tb00152.x | journal = JAMA (Reprinted in Obesity Research) | year = 1942 | author1 = Behnke AR | author2 = Feen BG | author3 = Welham WC | pages = 495–498 | volume = 118 | title = The Specific Gravity of Healthy Men| issue = 3 | pmid = 7627779 }}</ref> is based on [[Archimedes' principle]], which states that:
-The procedure is based on [[Archimedes' principle]], which states that:
-'''The buoyant force which water exerts on an immersed object is equal to the weight of water that the object displaces.'''
+''The buoyant force which water exerts on an immersed object is equal to the weight of water that the object displaces.''
-Example 1: If a block of solid stone weighs 3 kilograms on dry land and 2 kilogram when immersed in a tub of water, then it has displaced 1 kilogram of water.  Since 1 liter of water weighs 1 kilogram (at 4° C), it follows that the volume of the block is 1 liter and the density (mass/volume) of the stone is 3 kilograms/liter.
+Example 1: If a block of solid stone weighs 3 kilograms on dry land and 2 kilogram when immersed in a tub of water, then it has displaced 1 kilogram of water.  Since 1 liter of water weighs 1 kilogram (at 4&nbsp;°C), it follows that the volume of the block is 1 liter and the density (mass/volume) of the stone is 3 kilograms/liter.
-Example 2:  Consider a larger block of the same stone material as in Example 1 but with a 1 liter cavity inside of the same amount of stone.  The block would still weigh 3 kilograms on dry land (ignoring the weight of air in the cavity) but it would now displace 2 liters of water so its immersed weight would be only 1 kilogram (at 4° C).
+Example 2:  Consider a larger block of the same stone material as in Example 1 but with a 1-liter cavity inside of the same amount of stone.  The block would still weigh 3 kilograms on dry land (ignoring the weight of air in the cavity) but it would now displace 2 liters of water so its immersed weight would be only 1 kilogram (at 4&nbsp;°C).
-In either of the examples above, the correct density can be calculated by the following equation:
+In either of the examples above, the correct density can be calculated by the following equation:<ref>{{cite book |last1=McArdle |first1=William D |last2=Katch |first2=Frank I |last3=Katch |first3=Victor L |title=Exercise Physiology: Energy, Nutrition, and Human Performance|publisher=Lippincott Williams & Wilkins |year=2010 |isbn=978-0-7817-4990-9 | page = 741|edition=7th }}</ref>
-:<math> \mbox{Db} = \frac{\mbox{Ma}}{\mbox{(Ma - Mw) ÷ Dw - RV}} </math>
+:<math>D_b = \frac{M_a}{\frac{M_a - M_w}{D_w} - RV} </math>
+Where:
-Where:  Db = Density of the body, Ma = "Mass in air" (i.e. dry weight), Mw = "Mass in water" (i.e. underwater weight), Dw = Density of water (based on water temperature), RV = Residual volume (the unfilled space enclosed by the body- e.g. volume of air in the lungs + respiratory passages after a maximum exhalation).
+*{{mvar|D{{sub|b}}}} = Density of the body;
+*{{mvar|M{{sub|a}}}} = "Mass in air" (i.e. dry weight);
+*{{mvar|M{{sub|w}}}} = "Mass in water" (i.e. underwater weight);
+*{{mvar|D{{sub|w}}}} = Density of water (based on water temperature);
+*{{mvar|RV}} = Residual volume (the unfilled space enclosed by the body- e.g. volume of air in the lungs + respiratory passages after a maximum exhalation).
-The [[residual volume]] in the lungs can add error if not measured directly or estimated accurately. [[Residual volume]] can be measured by gas dilution procedures or estimated from a person's age and height: <ref>{{cite journal | author = Quanjer P.H., Ed. | title = Standardized Lung Function Testing | publisher = European Community for Coal and Steel, Luxembourg | year = 1983}}</ref>
+The [[Lung volumes|residual volume]] in the lungs can add error if not measured directly or estimated accurately. [[Lung volumes|Residual volume]] can be measured by gas dilution procedures or estimated from a person's age and height:<ref>{{cite journal | author = Quanjer P.H., Ed. | title = Standardized Lung Function Testing | publisher = European Community for Coal and Steel, Luxembourg | year = 1983 | journal = Bulletin Européen de Physiopathologie Respiratoire | volume = 19 | issue = suppl. 5 | pages = 1–95}}</ref>
- Inches:  RV-Est(Men) = 0.033 X Ht. (inches) + 0.022 X Age (yrs.) - 1.232
+* RV-Est(liters, Men) = 1.310 × Ht. (meters) + 0.022 × Age (yrs., take as 25 for 18-25) − 1.232
- Metric:  RV-Est(Men) = 1.310 X Ht. (meters) + 0.022 X Age (yrs.) - 1.232
+* RV-Est(liters, Women) = 1.812 × Ht. (meters) + 0.016 × Age (yrs., take as 25 for 18-25) − 2.003
+These estimates are for adults aged 18-70, have standard deviation of about 0.4 litres and have dependence on ethnicity, environmental factors, etc.<ref>{{cite journal | journal = European Respiratory Journal | year = 1993 | title = Lung volumes and forced ventilatory flows | doi = 10.1183/09041950.005s1693 | volume = 6 | pages = 5–40 | author1 = Ph.H Quanjer | author2 = G.J. Tammeling | author3 = J.E. Cotes | author4= O.F. Pedersen | author5= R. Peslin | author6= J-C. Yernault| issue = suppl. 16 }}</ref> [[Lung volumes|Residual volume]] may also be estimated as a proportion of [[vital capacity]] (0.24 for men and 0.28 for women).<ref>{{cite journal | author = Wilmore, J. H. | title = The use of actual predicted and constant residual volumes in the assessment of body composition by underwater weighing | journal = Med Sci Sports | year = 1969 | volume = 1 | issue = 2 | pages = 87–90 | doi=10.1249/00005768-196906000-00006| doi-access = free }}</ref>
- Inches:  RV-Est(Women) = 0.046 X Ht. (inches) + 0.016 X Age (yrs.) - 2.003
- Metric:  RV-Est(Women) = 1.812 X Ht. (meters) + 0.016 X Age (yrs.) - 2.003
-[[Residual volume]] may also be estimated as a proportion of [[vital capacity]] (0.24 for men and 0.28 for women).<ref>{{cite journal | author = Wilmore, J. H. | title = The use of actual predicted and constant residual volumes in the assessment of body composition by underwater weighing | journal = Med Sci Sports | year = 1969 | volume = 1 | pages = 87–90 | doi=10.1249/00005768-196906000-00006}}</ref>
 ==Application==
-Once body density has been calculated from the data obtained by hydrostatic/underwater weighing, [[body composition]] can be estimated.  The most commonly used equations for estimating the percent of body fat from density are those of Siri<ref name="siri">{{citation | author = Siri, SE | chapter = Body composition from fluid spaces and density: analysis of methods | editors = Brozek J, Henschel A | title = Techniques for measuring body composition | location = Washington, DC | publisher = [[United States National Academy of Sciences|National Academy of Sciences]], [[United States National Research Council|National Research Council]] | year = 1961 | pages = 223–34 }}</ref> and Brozek et al.:<ref name="brozek">{{citation | author = Brozek J, Grande F, Anderson JT, Keys A | title = Densitometric Analysis of Body Composition: Revision of some Quantitative Assumptions | journal = Ann. N. Y. Acad. Sci. | volume = 110 | pages = 113–40 |date=September 1963 | pmid = 14062375 | url = http://www.blackwell-synergy.com/openurl?genre=article&sid=nlm:pubmed&issn=0077-8923&date=1963&volume=110&spage=113 | doi = 10.1111/j.1749-6632.1963.tb17079.x}}</ref>
+Once body density has been calculated from the data obtained by hydrostatic/underwater weighing, [[body composition]] can be estimated.  The most commonly used equations for estimating the percent of body fat from density are those of Siri<ref name="siri">{{citation | author = Siri, SE | chapter = Body composition from fluid spaces and density: analysis of methods |veditors= Brozek J, Henschel A | title = Techniques for measuring body composition | location = Washington, DC | publisher = [[United States National Academy of Sciences|National Academy of Sciences]], [[United States National Research Council|National Research Council]] | year = 1961 | pages = 223–34 }}</ref> and Brozek et al.:<ref name="brozek">{{citation | vauthors = Brozek J, Grande F, Anderson JT, Keys A | title = Densitometric Analysis of Body Composition: Revision of some Quantitative Assumptions | journal = Ann. N. Y. Acad. Sci. | volume = 110 | pages = 113–40 | date = September 1963 | issue = 1 | pmid = 14062375 | doi = 10.1111/j.1749-6632.1963.tb17079.x | bibcode = 1963NYASA.110..113B | s2cid = 2191337 }}</ref>
 Siri (1956):  Fat %  = [4.950 /Density - 4.500]×100
@@ Line 39: / Line 41: @@
 *[[Body composition]]
 *[[Composition of the human body]]
+*[[Body fat percentage]]
 {{DEFAULTSORT:Hydrostatic Weighing}}
-[[Category:Obesity]]
+[[Category:Anthropometry]]
+[[Category:Classification of obesity]]

Latest revision as of 21:40, 4 December 2024

Method

Application

References

See also