Аннотация:The temperature dependences of the tension and stiffness of actively contracting single fibers of therabbit slow muscle (m. soleus) were studied using the Joule temperature jump. Differences in the character-istics of the fibers of the rabbit fast (m. psoas) and slow (m. soleus) muscles were shown; apparently, they werecaused by differences in the kinetics of the myosin head cycle.