The surface-tension theory of muscular contraction

Abstract

It was shown by Bernstein (1) in 1908 that the maximum mechanical response in a muscle twitch is greater at a lower temperature. Since surface tension decreases as the temperature is raised, this observation was regarded as strong evidence in favour of the theory that “ changes in surface tension are a controlling factor in the development of the energy of muscular contraction ” (Bayliss (2), p. 448); other physical effects such as osmotic pressure and “ Quellung ” were, according to Bernstein, excluded since these increase as the temperature is raised. If it had been shown at the same time that the total energy liberated in a muscular contraction was independent of temperature, the mechanical energy alone varying, this might indeed have been regarded as in favour of a surface-tension theory. Actually, however, the total heat set free in a twitch decreases as the temperature is raised, in just the same way as does the tension; indeed, there is a very constant relation between the two, so that for a given liberation of total energy , i. e., for a given chemical change , the tension energy set free is independent of the temperature . Bernstein’s observation, therefore, gives us no grounds for concluding that the development of the mechanical response in muscle is due in any way to changes of surface tension. To put the matter in terms of lactic acid, a given production of lactic acid is accompanied by the same rise of tension whatever the temperature. If further evidence be required against the deduction from Bernstein’s observations it is supplied by the fact that in a tetanic contraction the tension developed and the heat set free are both greater, and not less, at the higher temperature. When a frog’s muscle is maintained in a constant state of contraction by a succession of stimuli, the tension is not lower at a higher temperature, as it should be on the surface-tension theory, but appreciably higher. Another explanation of these facts has been given by Hartree and Hill (3, p. 141).