Wave-like variations in muscular fatigue curves / by C.T. Symons.

  • Symons, C. T.
Date:
[1908?]
Catalogue details

Licence: Public Domain Mark

Credit: Wave-like variations in muscular fatigue curves / by C.T. Symons. Source: Wellcome Collection.

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    support of the lever at the beginning of each contraction. This seems hardly adequate to account for the change, since if the lever be supported at different levels by means of a stop, during the production of the waves no apparent change is induced. Also if a support be used throughout the interrupted series of contractions, a stage can be reached, at which the initial contraction after a pause is able to lift the lever a considerable distance, then in the first trough the summit line sinks below the level of the support, but the following crest may rise just above this level, so that the tracing shows a short period during which no contractions are recorded. In some experiments where the waves appeared early in the fatigue, at a time when the relaxation was still rapid and when there was thus a considerable throw-down of the lever below its stationary relaxation level, waves appeared on the line formed by joining the lowest points to which the throw-down carried the lever (Fig. 11). Injections of cocaine, atropine, or supra-renal preparations were without effect on the production of the waves, as were also ether and chloroform vapour in quantities which left the muscle still excitable. And, indeed, it was found that, in the case of any muscle which would produce the waves when fatigued under ordinary conditions, the influence of no external agent, except extremes of heat and cold, could prevent their occurrence. In certain frogs the gastrocnemius would not show the variations; and this was also the case when there were marked irregularities in the summit line at the beginning of an experiment. For the appearance of the waves in the most evident form, constancy and regularity of excitation, combined with some fairly rapid interruption, are essential. Summary. 1. When certain frogs’, toads’, and mammalian muscles are fatigued under constant conditions with maximal break induction shocks, temporary wave-like variations can be produced in the summit line during the later stages of fatigue, by any alteration in : (a) load, (6) rate of stimulation, (c) temperature, and also by introducing short periods of rest or of sub-maximal stimulation. 2. These variations can be evoked in the frog’s gastrocnemius in winter as well as summer animals, whether the muscle be in the circulation or isolated, whether the stimulation be direct or indirect,