The influence of temperature on the isometric characteristics of fast and slow muscle in the cat.

The maximum tetanic tension (initial strength) and the length of time, 20, 40 or 60%, of that initial strength could be maintained (endurance) was assessed in 2 fast twitch muscles (the plantaris and the medial gastrocnemius) and a slow twitch muscle (the soleus) of the cat at muscle temperatures ranging between 22 and 38 degrees C. The results of these experiments showed that the strength of the soleus was constant between muscle temperatures of 38 to 28 degrees C, and then gradually decreased as the muscle was cooled further. Plantaris, on the other hand, showed a reduction in strength at all muscle temperatures less than 38 degrees C; the response of the medial gastrocnemius was between these two extremes. The longest endurance for the soleus muscle was found to be at a muscle temperature of 28 degrees C, the endurance being as much as 3 times higher at this temperature than at muscle temperatures of 22 or 38 degrees C. The medial gastrocnemius showed a similar response but the endurance only doubled when comparing the endurance at a muscle temperature of 28 to 38 degrees C. In contrast, the plantaris maintained a constant endurance over the temperature range of 38 to 28 degrees C; below this muscle temperature the endurance decreased markedly. The mechanism for this response appeared to be related to the effect of temperature on the contractile characteristics of the muscles.