Exercise and the management of diabetes mellitus

Fuel metabolism in individuals with well-controlled diabetes is similar to that occurring in persons who do not have diabetes. During the initial phase of physical exercise, muscle glycogen is the primary source of fuel. As exercise continues, blood glucose and free fatty acids (FFAs) become increasingly important substrates. FFAs become the major fuel source as glucose utilization decreases. Whereas in individuals who do not have diabetes, blood glucose levels vary little during exercise, the person with insulin-dependent diabetes mellitus (IDDM) may experience an increase in blood glucose, a modest decrease, or a marked decrease, which can result in hypoglycemia. In insulin-treated persons with mild hyperglycemia, exercise is accompanied by a fall in blood glucose. In contrast, in persons with marked hyperglycemia and ketosis, exercise may cause a further rise in both blood glucose and ketone levels. The glycemic response to exercise is dependent on the plasma concentration of insulin. Physical training improves glucose tolerance in individuals with noninsulin-dependent diabetes mellitus (NIDDM); in persons with IDDM, it may diminish insulin requirements. The repletion of muscle and liver glycogen, which takes place for 24 to 48 hours after exercise, requires a minimum amount of insulin in addition to carbohydrate feeding. Persons using insulin may need to increase food intake prior to, during, and after exercise and/or decrease insulin dosage as well. Persons with IDDM can exercise safely, and persons with NIDDM can achieve better control by following the guidelines outlined for exercise prescription.