Adaptation of connective tissue length to immobilization in the lengthened and shortened positions in cat soleus muscle.

1. The aim of this study was to investigate length adaptation of connective tissue in adult cat soleus muscle immobilized in the lengthened position for 28 days (group I) or in the shortened position for 14 (group II) or 28 days (group II). 2. The method, combining passive tension-length curves of the whole muscle with measurement of the length of the contractile part of isolated fibres, enabled separate determination of length of the very slightly compliant tendinous part, and of the highly compliant parallel elastic component (PEC) mainly constituted of belly connective tissue. 3. PEC length was found to increase in group I and to shorten in group II and III, showing that it adapted to the length imposed on the muscle. 4. Tendinous part lengths did not change significantly in any of the three groups compared to the controls. 5. Comparison of the respective adaptations of PEC and contractile tissue lengths showed that PEC adaptation was insufficient in groups II and III.