The effects of physical training on skeletal muscle morphology and enzyme activities were compared in 10 male, type I diabetic subjects and 10 healthy, male, control subjects. The training program consisted of running for 45 min, three times per week for 8 wk. Muscle biopsies were obtained before and after the training period from the lateral portion of the gastrocnemius muscle. Pretraining maximal oxygen uptake was similar in the two groups (diabetic subjects 42 ± 1 versus control subjects 43 ± 2 ml × kg−1 × min−1), and the training resulted in an identical increase (+ 13%, P < 0.01). Muscle capillarization (number of capillaries per muscle fiber) increased on the average in the control group (+ 14 ± 4%, P < 0.01), but was unchanged in the diabetic group (0 ± 4%). Capillary density, expressed as number of capillaries per unit muscle cross sectional area, also increased on the average in controls (8 ± 4%, P < 0.05) but failed to do so in the diabetic patients (–8 ± 6%, NS). The activities of the mitochondrial enzymes citrate synthase (+ 26–27%, P < 0.01–0.05) and succinate dehydrogenase (+ 24–25%, P < 0.05) increased significantly and similarly in the two groups, whereas training did not result in significant changes in the activities of the glycolytic enzymes 6-phosphofructokinase and glyceraldehyde-phosphate dehydrogenase. Glycemie control in the diabetic group did not improve with the training, as evaluated from hemoglobin A1 and home-monitored blood glucose.

The findings suggest that, compared with controls, the ability to form new skeletal muscle capillaries in response to physical training may be deficient in patients with type I diabetes mellitus of long standing, while the increase in mitochondrial enzyme activities is normal. A deficient formation of new capillaries may be an expression of the microangiopathy of this disorder.

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