Exercise is conventionally considered a modality for improvement of glycemia in diabetes. We have found that a short period of intense exercise (80% 
) in normal lean subjects produces sustained postexercise hyperglycemia 20% above basal with a corresponding 100% increase in plasma insulin. In people with insulindependent diabetes mellitus (IDDM) incapable of this insulin response, it was predicted that postexercise hyperglycemia would be of greater magnitude and/or duration. To investigate this possibility, the effects of the same intense exercise (80% 
) were studied in 8 IDDM subjects (2 on 2 occasions) in the postabsorptive state with continuous subcutaneous (abdominal) insulin infusion (CSII). When the preexercise plasma glucose was normal (n = 6, 86 ± 4 mg/dl), there ensued a postexercise hyperglycemia to 127 ± 7 mg/dl (P < .001) sustained for 2 h postexhaustion. Plasma free immunoreactive insulin (IRI) was 1.43 ± 0.12 ng/ml before exercise and did not change postexercise. When mean preexercise plasma glucose was 149 ± 9 mg/dl (n = 4), it rose progressively throughout the 2 h of recovery to 229 ± 28 mg/dl (P < .025). A small but statistically significant decrease in free IRI occurred during the last 80 min of recovery. Hyperglycemia in the diabetic subjects was not explained by abnormal or differing responses of glucagon or catecholamines. Thus, with intense exercise, diabetic control deteriorates rather than improves. Therefore, different therapeutic strategies may be required for intense compared with moderate exercise in IDDM patients.
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