Regular aerobic exercise improves blood circulation and lowers blood glucose levels. Exercise also strengthens the heart and helps maintain an ideal body weight. The chosen aerobic exercise should use large muscle groups. Running, walking, biking, and swimming are excellent activities for most people. The frequency, type, and duration of exercise depend on the individual's age, treatment goals, and physical ability. An exercise program should be designed with the help of a healthcare provider.
Exercise increases or decreases blood glucose levels depending on the concentration of glucose and insulin in the blood at the time of the exercise. If blood glucose is low or normal, exercise may cause hypoglycemia (low blood glucose) due to the utilization of glucose by the active muscles. On the other hand, exercise may cause hyperglycemia (high blood glucose) if there isn't enough insulin to allow the active muscles to utilize blood glucose. As a result, the muscles signal the body to produce more glucose, and the glucose accumulates in the blood. Therefore, food intake and insulin doses should be adjusted based on the intensity and duration of the anticipated exercise.
Source : medicinenet.com