FUNCTIONAL ADAPTATION OF SASCOMERE NUMBER OF NORMAL CAT MUSCLE

  • 1 January 1976
    • journal article
    • research article
    • Vol. 72  (3) , 277-291
Abstract
Physiological and histological data were obtained from soleus and tibialis anterior muscles of normal adult cats to study to what extent fiber length and sarcomere number varied between animals and how this was related to the physiological characteristics of the muscles. For a given muscle the variation in the sarcomere number of individual muscle fibers between animals was .apprx. 25%. These differences could partly be explained by comparing the number of sarcomeres and the length of the fibula, which was chosen as an index of the size of the animal. The average sarcomere number in the tibialis anterior muscle was .apprx. 60% greater than in the soleus. The variations between animals and between the anterior tibialis and soleus muscles were significantly greater than the variations within the same muscle. Sarcomere length is dependent upon the articular angle, i.e., the length change imposed on the muscle. These length changes are more extensive in the soleus muscle (100%) than in the tibialis anterior muscle (60%). A very significant correlation was found between articular angle and sarcomere length (for soleus r = 0.98, for tibialis anterior r = 0.94). Although fiber length varied considerably within a given muscle, sarcomere length showed only minor variations at any given angle. Sarcomere number is probably determined in each individual muscle fiber. Such an adaptation implies a concomitant adaptation of the tendinous part of the fiber. This adaptation, resulting in definite sarcomere length at a definite angle, has obvious physiological implications. Conventional length vs. active tension curves were established for the soleus and the tibialis anterior muscles. The difference between the sarcomere number of the 2 muscles may result in the difference between the shapes of the 2 curves. Active torque-angle curves were established for the 2 muscles in situ. The shapes of the curves for soleus and tibialis anterior are similar in spite of the indifferent mechanical conditions. This helps to explain why the 2 muscles, despite their similar articular range, had very different sarcomere number.

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