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An Olympic weightlifter asked me this question and it has been bugging me for a couple of days now.

Suppose "lower part" is defined as anything below and including the hip. This means that the majority of the mass and density is determined by the muscles and bones of the legs and hips.

I've been trying to solve this via the relationship between the mass, density and volume of an object, using Archimedes' principle, etc.

While this approach can find the density and volume of the whole body, it can only give us the volume of the lower part, with the lower body mass and density remaining unknown.

Approximating the lower body mass via the lower body volume and the total body density would not be appropriate, since there's bound to be major differences in density - the legs are mostly skeletal and muscle tissue, while the upper body hosts most of the major organs.

Is there another approach that may yield the correct answer? Maybe measuring the conductivity of only the lower body would give a better estimation of its density, but how do we measure that?

Note: I already asked if amputation is an option and the suggestion was not met with enthusiasm.

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    $\begingroup$ Possible duplicate of How can you weigh your own head in an accurate way? $\endgroup$ – John Rennie Jan 12 '16 at 11:27
  • $\begingroup$ The answers to the question I've linked are mostly facetious, however it is a duplicate insofar as the methods used for determining the weight will work for determining the weight of the lower half of your body. $\endgroup$ – John Rennie Jan 12 '16 at 11:29
  • $\begingroup$ Thanks, I tried to find duplicates before posting, but couldn't. Gonna take a look now. $\endgroup$ – npace Jan 12 '16 at 11:32
  • $\begingroup$ Read the duplicate suggestion, quite funny. $\endgroup$ – Ed Yablecki Jan 12 '16 at 12:25
  • $\begingroup$ "Eureka!" (google it :-) ) $\endgroup$ – Carl Witthoft Jan 12 '16 at 14:17
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With some prior measurements such as total mass, volume of lower and upper body. I think you can use these techniques to figure the mass of just lower body.

Computerized Tomography (CT) and Magnetic Resonance Imaging (MRI)

These two imaging techniques are now considered to be the most accurate methods for measuring tissue, organ, and whole-body fat mass as well as lean muscle mass and bone mass. (1) CT and MRI scans are typically only used for this purpose in research settings.

Strengths

•Accurate •Allows for measurement of specific body fat compartments, such as abdominal fat and subcutaneous fat

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