THE MAXIMAL ISOMETRIC TETANIC TENSIONS DEVELOPED BY MAMMALIAN MUSCLE, IN SITU, AT DIFFERENT TEMPERATURES

¹ Medical Research Council Unit for Research in Climate and Working Efficiency, Department of Anatomy, Oxford

Variations in the maximum isometric tetanic tension developed at different muscle temperatures have been examined following direct and indirect stimulation of the tibialis anterior muscle of the cat. While the frequency of direct stimulation necessary to evoke maximum tension remained constant at about 120-160 cycles/sec., the frequency of indirect stimulation had to be varied with temperature to ensure supramaximal stimulation. At such optimal frequencies of indirect stimulation for different muscle temperatures, the length-tension relationship remained unaltered at muscle temperatures between 20 and 40°C.

Maximum isometric tetanic tensions were greatest at 38-40° C. A fall in muscle temperature to about 28° C. resulted in a fall in tension of only 5 per cent below that found at 40° C., but a further fall in muscle temperature to about 20° C. led to a reduction in the tension exerted to a value of 30-35 per cent less than that exerted at 40° C. Such tensions were slightly greater when evoked by direct than by indirect stimulation. The amount of this difference was 2-4 per cent at 40° C. and 7-8 per cent at 20° C. The evidence suggests, therefore, that when the frequency of stimulation is adjusted to the optimal rate for given temperatures, the greater proportion of the fall in tension is due to failure within the muscle fibre itself rather than to failure of the neuromuscular junction. The relationship of this finding to voluntary contractions is discussed.

Note:

We wish to thank Mr. E. S. Reeves for his valuable technical assistance.