Diabetes was produced by withholding insulin treatment from previously alloxanized female rats. Isometric contraction was assessed in soleus and extensor digitorum longus (EDL) muscles removed 2 h to 32 days after insulin withdrawal. Directly induced contractions were measured in vitro at 20°C. In soleus muscles from severely diabetic rats, average twitch and tetanic forces were normal or slightly greater than that of controls of similar age, whereas in EDL, marked decreases appeared in both twitch and tetanic forces. Soleus muscle from severely diabetic rats was not depolarized as already reported in EDL. After 16 and 32 days in the diabetic state, soleus muscles from moderately diabetic rats generated average tetanic forces that were equal to that found in age-matched controls, whereas EDL tetanic forces were significantly (P = <0.01) weaker. Average specific twitch force in diabetic soleus muscles was greater than age-matched controls after 16 and 32 days in the diabetic state. In diabetic soleus muscle, significant increases in the average half relaxation time and twitch duration were seen after prolonged (16 and 32 days) periods of diabetes. No changes were seen in the same temporal parameters of the twitch in diabetic EDL muscle. A greater atrophy appeared in EDL than in soleus after 16 and 32 days of uncontrolled diabetes.

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