The physiology of muscular exercise / by F.A. Bainbridge.

  • Bainbridge, F. A. (Francis Arthur), 1874-1921.
Date:
1919
Catalogue details

Licence: In copyright

Credit: The physiology of muscular exercise / by F.A. Bainbridge. Source: Wellcome Collection.

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    if it is not allowed to shorten, the surface energy is dissipated as heat. But some difference of opinion exists as to the form in which its potential energy is stored in the muscle. A. V. Hill holds that some unstable chemical complex is present, which, under the influence of a stimulus, is decomposed, lactic acid being formed, and the energy, furnished by this decomposition, being converted into surface energy. After the contraction is over, the lactic acid is once more built up into the chemical complex, the energy required for this purpose being obtained from the oxida¬ tion of fat or carbohydrate within the muscle. Fletcher and Hopkins, on the contrary, consider that the potential energy resides “ in a particular condition of a physico-chemical system,” and that a system of colloidal fibrils or longitudinal surfaces, such as is assumed to exist in muscle, possesses a potential of energy which may be discharged as work or heat when H' ions are brought into relation with it. They believe that the formation of lactic acid from glucose, by setting free H • ions, initiates the discharge of part of this energy in the form of a muscular con¬ traction ; the return of the colloidal system to its former resting condition, and the restoration of its potential energy, are effected at the expense of the energy furnished by the oxidation of lactic acid after the contraction is over. There is every reason to believe that in muscle, as elsewhere in the body, lactic acid appears as an intermediate stage in the combustion of carbohydrate, and Parnas and Wagner (1914) have shown that the appearance of lactic acid coincides with a diminution of the carbohydrate content of isolated muscle. But, in muscle, to quote Fletcher and Hopkins, lactic acid has “ its special role to play in connection with the muscle machinery. In the evolution of muscle it would appear that advantage, so to speak, has been taken of this acid phase in carbohydrate degrada¬ tion, and that, by appropriate arrangement of the cell-elements, the lactic acid, before it leaves the tissue in its final combustion, is assigned the particular position in which it can induce those tension changes upon which all the wonders of animal movement depend.” The logical deduction, which springs from this conception of the nature of muscular contraction, is that the carbohydrate stored in the muscles, and elsewhere in the body, furnishes the main reservoir of energy upon which the muscles draw for the carrying