RELATIONSHIP BETWEEN SARCOMERE LENGTH IN SOLEUS AND TIBIALIS ANTERIOR AND ARTICULAR ANGLE OF TIBIA-CALCANEUM IN CATS DURING GROWTH

Abstract

Modifications of sarcomere length with growth was studied for a given ankle angle. Sarcomere number and sarcomere length of single muscle fibers were measured in 6 groups of kittens ranging in age from 10 min.-5 mo. and compared with those of adult cats. Sarcomere number increased during growth and was well correlated with the fibula lengths. The total sarcomere numbers for soleus and tibialis anterior muscles differed markedly. The ratios between the sarcomere numbers of these muscles did not differ significantly during growth. During the same period the tibialis anterior muscle, initially a slow contracting muscle, became a fast contracting muscle. The sarcomere length for a given ankle angle was the same at all ages, except perhaps for the newborn. The soleus and tibialis anterior muscles had the same range relative to ankle movement. The relationship between relative active tension and relative muscle length were measured. No difference was found between the muscles at any age although the shape of the curves for the soleus and tibialis anterior were different.