The relationship between sarcomere length in the soleus and tibialis anterior and the articular angle of the tibia-calcaneum in cats during growth.

Sarcomere number and sarcomere length were studied in six groups of kittens ranging in age from 10 minutes to 5 months and compared with those of adult cats. Although the soleus muscle is a slow contracting muscle and the tibialis anterior a fast contracting muscle, both have previously been shown to have the same range relative to ankle movement. For a given angle of articulation the sarcomere length was found to be the same at all ages except perhaps for the newly born. In contrast, the sarcomere number differed considerably, being much higher in the older animals. The relationship between active tension and muscle length was also measured, and again no difference was found between the muscles at any age, although the shape of the curves for the soleus and tibialis anterior was different.