Measure body fat with only a gallon jug (and a couple thousand tons of water)

I finally got around to uploading the PDF version of my body fat measurement quest, and also a simplified one-page PDF for those of you that just want to try it out and don’t want to wade through all the physics and my ramblings. While I was at it I threw together an OpenOffice.org spreadsheet to do all the heavy math for you too. Now the only difficulty is finding a couple thousand tons of water laying around. I put together a simple page with links to all that stuff I just mentioned (except the water).

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2 Responses to “Measure body fat with only a gallon jug (and a couple thousand tons of water)”

  • FuglDad Says:
    November 24th, 2007 at 08:35

    We happened to be going the pool yesterday and decided to give the body fat measurements another try.

    This time we tried measuring our VC and converting it for BTPS in hopes of getting better accuracy. I then compared the results to the skin fold method, BMI, and two body measurement methods – girth and weight for the males and hips and height for the female and also the Navy tables which include waist or hips, neck and height.

    The test subjects were 1) male age 53, 2) male age 15, and 3) female age 17. Here are the results:

    Subject 1:

    • weight – 254.4 lbs
    • height – 6′ 4″
    • hydrostatic – 25.3%
    • skinfold – 28%
    • Navy body measurement – 24%
    • waist & weight – 25%
    • BMI – 31%

    Subject 2:

    • weight – 170.4 lbs
    • height – 6′ 1.5″
    • hydrostatic – 17.3%
    • skinfold – 17%
    • Navy body measurement – 10%
    • waist & weight – 12%
    • BMI – 22.2%

    Subject 3:

    • weight – 168.4 lbs
    • height – 5′ 11″
    • hydrostatic – 28.9%
    • skinfold – 25%
    • Navy body measurement – 29%
    • hip & height – 29.5%
    • BMI – 23.5%

    Observations:

    BMI is way off. High for the males and low for the female.

    Body measurement methods have good corrilation with other measurements with the very notable exception of the 15 year old male. Since a 17 year old female will generally have an essentially adult body, the implication is that body measurement methods are only reliable with adults.

    The degree of correlation between most of the methods gives good confidence for your method. with the additional step to try to get a better handle on VC, I feel confident that the improvised hydrostatic method give the most reliable results.

    My BTPS correction for VC was estimated at 1.082 due to somewhat higher altitude here.

    Hope you find these results interesting and useful. I found the excersise fun and informative.

    Dad

  • Hans Says:
    November 24th, 2007 at 09:07

    Thanks for the experiments! It’s good to see the correlation there. It’s definitely the case, from what I’ve read, that the body fat measurement methods are designed for adult bodies. This also goes for the equations used in the hydrostatic method.

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