Our everyday experience demonstrates that muscular activity is accompanied by heat production. It is necessary to take account of this when studying the energy released by muscle. Much of our knowledge is based on that acquired by A. V. Hill and his colleagues from many years' work on isolated frog muscles. In most experiments the muscle is laid over a thermopile — an array of thermocouples arranged in series — so that very small changes in temperature can be measured.
During an isometric tetanus, heat is released at a very high rate for the first 50 ms or so (this is usually called the activation heat), falling rapidly to a lower more steady level which is usually called the maintenance heat (Fig. 9.12). If the muscle is allowed to shorten, an extra amount of heat is released during the shortening process. This heat of shortening is roughly proportional to the distance shortened. Further heat appears during relaxation, especially if the load does
work on the muscle. Finally, after relaxation, there is a prolonged recovery heat as the muscle metabolism restores the chemical situation in the muscle to what it was before the contraction took place.
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Among the evils which a vitiated appetite has fastened upon mankind, those that arise from the use of Tobacco hold a prominent place, and call loudly for reform. We pity the poor Chinese, who stupifies body and mind with opium, and the wretched Hindoo, who is under a similar slavery to his favorite plant, the Betel but we present the humiliating spectacle of an enlightened and christian nation, wasting annually more than twenty-five millions of dollars, and destroying the health and the lives of thousands, by a practice not at all less degrading than that of the Chinese or Hindoo.