Littell's Living Age/Volume 136/Issue 1759/Miscellany
Heat Phenomena and Muscular Action. — On reading the article which appeared in Nature, vol. xvi., p. 451, on the heat phenomena accompanying muscular action, it has occurred to me to send the following problem which is akin to the subject.
If a man does work (say lifts a weight), the principle of the conservation of energy teaches us that the potential energy — the work done — (weight lifted) is at the expense of the man as a magazine of force, in fact that "virtue has gone out of him." Now suppose a man lifts say a ton of bricks and deposits the bricks one by one on the top of a wall six feet high, we can exactly estimate the amount of work done, the energy rendered potential and external, and if we knew also the extra amount of heat radiated or otherwise carried off from his body — as most probably the work would raise his temperature — we could exactly measure the amount of energy the lifting of the brick cost him.
Now suppose another man were to lift the bricks from the top of the wall and deposit them gently — i.e., without concussion — on the ground, it is evident that there is a certain amount of potential energy disappearing, in fact that there is work being absorbed by the man, of course appearing in some other form, but the question is how? This second man's work is of course in one sense work, but in the sense of producing external, potential, or kinetic energy, is not so, unless, perhaps, in heat.
Strangely enough it follows that lifting down the brick ought to make the man either radiate heat more, waste tissue less, digest food less, or in some other way account for the energy absorbed by him.
Generally I think the conversion of force by obstruction is not always so clearly traced as it might be; in friction it is clear, as also in the compression of elastic bodies, but in the instance above, as also in the throttling of steam, it is not so clear. Nature.A. R. Molison.