Effects of Exercise in Diabetics

Metabolic Effects
During exercise at maximal levels energy demands may be 20-fold increased as compared to resting conditions.

In order to maintain homeostasis and prevent hypoglycemia several regulatory mechanisms are activated. Initially skeletal muscles break down their own stores of glycogen, triglycerides, and free fatty acids derived from adipose tissue. In order to mobilize extramuscular stores adjustments on a hormonal basis are necessary.

In the early phase of exercise hepatic glucose production is increased by a reduction of insulin levels in the presence of unchanged glucagon levels. In subsequent stages glucagon and catecholamine levels are elevated. As a result, glucose levels in healthy individuals remain fairly constant during exercise.

In patients with diabetes type 2 exercise of moderate or high intensity regularly decreases blood glucose levels as a result of insulin-independent activation of glucose transport (7) as well as increased insulin sensitivity (8). Due to an exaggerated counter-regulatory response in the postexercise period hyperglycemia and hyperinsulinemia is frequently encountered in patients with type 2 diabetes.

Following a meal most of the glucose contained in it is rapidly taken up by skeletal muscle and deposited as glycogen. In addition, exercise per se is a powerful stimulator of glucose uptake; part of this action is explained by the increase of skeletal muscle glucose transporter protein (GLUT4) in healthy individuals as well as in patients with type 2 diabetes; it is responsible for insulin-independent glucose transport into skeletal muscle.

Following a session of exercise with total depletion of muscular glycogen stores sufficient amounts of glucose need to be absorbed in order to replenish the stores resulting in an increase of insulin sensitivity for more than 72 hours. Conversely, after 6 months of training insulin sensitivity returned to baseline after only 72 hours of sedentary lifestyle, underlining the importance of persistent and regular exercise (9).

Regular physical activity is associated with changes in body composition with a reduction in body fat, increase in muscle mass, and maximal oxygen uptake in healthy individuals; insulin sensitivity is closely correlated to these factors. Corresponding results are obtained in patients with diabetes type 2 who engage in a structured exercise program.

Improvements of insulin sensitivity are independently correlated to a reduction in abdominal obesity and an increase in muscle cross-sectional area (10).

The benefits of exercise, however, are only maintained for short periods of time; they attenuate 3 to 6 days after the last exercise session stressing the importance of persistent lifestyle changes . By adding resistance training to aerobic exercise muscle mass may be increased, particularly in elderly patients who tend to loose muscle mass as a result of aging .