Exercise is being increasingly promoted as part of the therapeutic regimen for diabetes mellitus. In addition to its cardiovascular benefits, exercise can also improve glycemic control. The beneficial effect on glycemic control largely results from increased tissue sensitivity to insulin.
To understand how these changes occur, it is helpful to begin by briefly reviewing the short- and long-term effects of exercise in normal individuals. Subsequently, the benefits of exercise in patients with type 1 and 2 diabetes and a program for physical activity will be reviewed in this topic card.
The glycemic benefits of combined diet and exercise interventions in patients with diabetes, exercise for the prevention of type 2 diabetes, and sample cases illustrating problems that can occur when exercise is performed in patients treated with an intensive insulin regimen are discussed separately. (See "Initial management of blood glucose in adults with type 2 diabetes mellitus", section on 'Intensive lifestyle modification' and "Prevention of type 2 diabetes mellitus", section on 'Exercise' and "Cases illustrating the effects of exercise in intensive insulin therapy for diabetes mellitus".)
EXERCISE AND MUSCLE METABOLISM
Exercise has both short-term and long-term effects on metabolism in nondiabetic subjects .
Short-term effects — As a person exercises, the muscles initially use glucose in the muscle and later convert muscle glycogen to glucose to provide energy. An average 70 kg adult man has approximately 1100 kcal stored as muscle glycogen and another 400 to 500 kcal stored as liver glycogen. Skeletal muscle differs from liver in that it lacks the enzyme glucose-6-phosphatase, which converts glucose-6-phosphate (derived from glycogen) to glucose; as a result, muscle glycogen can only be used as an energy source for muscle via the metabolism of glucose-6-phosphate to pyruvate. Glucose cannot be transferred out of muscle to prevent hypoglycemia (figure 1).