how to calculate body fat by MaryJeanMenintigar

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									Name _______________________________
FCSN 442 - Nutrition Assessment Laboratory
Spring 2006
First Exam - Closed Book

1.        The 2000 ACSM/ADA Position Paper on Nutrition and Athletic Performance
          concludes that “because of errors associated with body composition assessment
          methods, it is inappropriate to set a specific body-fat percentage goal for an
          individual athlete.” Describe for each of the following field techniques for
          assessing body composition THREE significant and distinct sources of errors
          or questionable assumptions which result in these errors of assessing body

          NN.   Hydrodensitometry

Significant sources of error include:
   1.     assumes that the density of lean tissue is constant when it varies
          substantially from subject to subject.
   2.     estimations of residual lung volume and gastro-intestinal gas volume
          are often inaccurate.
   3.     accuracy of weighing subject underwater is compromised when subject
          is moving and causing the scale to move up and down.
   4.     inability of subject to exhale all air from lungs (minus residual lung

          OO.   Bioelectrical impedance analysis

     1.      assumes that water is a constant % of lean body mass when it is not
     2.      assumes subject is normally hydrated, which often is not the case
     3.      assumes subject body temperature is normal, which may not be true if
             subject exercised on way to measurement site
     4.      assumes that height accurately estimates conductor length, which may
             often not be true in long or short-limbed individuals

          PP.   Skinfold thickness measurement

     1.      assumes that skinfold sites measured are a reflection of total
             subcutaneous fat depots
     2.      assumes that skinfold thickness is related to the quantity of visceral fat.
     3.      assumes that skin thickness is negligible or constant.
     4.      assumes normal hydration
     5.      assumes subcutaneous fat has constant texture and that calipers
             applying the same force will compress fat equally from subject to
  2.    In the space provided, describe in words the theory behind how
        hydrodensitometry and bioelectrical impedance measure body composition.

        a. hydrodensitometry

The difference in a person’s weight in air and underwater is approximately
equal to their body volume (weight of the water displaced). Knowing body
volume and body weight, one can calculate body density and therefore %
body fat.

        b. bioelectrical impedance analysis
An electrical current through the body travels primarily through lean tissue
which has a high content of water and electrolytes. Impedance of a current
is related to the conductivity of the conductor, the length of the conductor,
and the cross-sectional area of the conductor. The conductivity of the
body is related to the total amount of body water. By assuming that lean
mass has a constant % water, one estimates lean mass and eventually fat

  3.    Jane Smith is a 75 year old newly admitted resident of the long term care
        facility that you work at. She has been placed there because she has been
        unable to care for herself due to Alzheimer’s Disease. She is currently 120
        pounds and is 5'3" tall. Knowing this, what would your initial assessment of
        her status include? Explain your conclusion.
Although her BMI calculates to 21 (normal body weight), it is difficult to
make any kind of initial assessment based on this one value by itself. It is
important to seek other assessment values and in particular, to find any
record of weight history as weight loss is common in this population.

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