Is head weight a constant fraction of body weight?

Nurses are among those most frequently injured on the job, says Daniel Zwerdling of NPR (in a long piece that’s worth reading). One of the most common sources of such injuries is lifting patients, which gets worse as we Americans get heavier.

There’s a chart that is a bit perplexing from a mathematical point of view, though. This chart claims, for example, that the weight of your head is seven percent of your body weight – regardless of that weight. (the trunk is 43 percent, each arm is 5, and each leg is 20.). These are based on “body segment parameters” from, as far as I can tell, a 1996 study by Paolo da Leva based on gamma-ray scanning by earlier researchers. The major use of this sort of work seems to be in studying how the body moves.

But I’d think, for example, that the weight of the head grows less slowly than overall weight – this comes from extensive looking at the heads of people of different weights – and other body parts more so to compensate. I don’t have a pile of cadavers or machines for scanning live subjects – any ideas?

One thought on “Is head weight a constant fraction of body weight?

  1. my first thought is that a study like this would need to isolate full-grown adults or something, because the heads of children seem much larger with respect to their body size than those of adults … (i read the abstract and the study is for college-aged males / females).

    a long way of saying my daughter has an enormous noggin’

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