Insulin therapy and exercise

Medical nutrition therapy and physical exercise are the cornerstones of the diabetes management. Patients with type 1 DM always need exogenous insulin administration, recently available in the form of insulin analogs. In type 2 DM, characterized by increased insulin resistance and progressive decline of the beta-cell function, various antidiabetic medications are used. Most of the subjects with type 2 DM will finally need insulin. The main site of insulin action is the skeletal muscle, while the liver is the main site of glucose storage in the form of glycogen. With the modern diabetes therapies it is possible to rapidly reach and maintain normoglycemia in both types of DM but with the cost of higher incidence of hypoglycemia, especially related to exercise. Regular physical exercise causes a lot of beneficial effects in healthy as well as diabetic subjects of all age groups. In type 1 DM physical exercise is a fundamental element for both physical and mental development. In type 2 DM it has a main role in diabetes control. The increased hepatic glucose production and the increased muscular glucose uptake during exercise are closely interrelated in all exercise intensities. In diabetes mellitus there is a disturbed energy substrate use during exercise leading to either hypo- or hyperglycemia. The influence of low or moderate intensity aerobic exercise on diabetes control has been well studied. The inappropriately high insulinemia combined with the low glucose levels can lead to severe hypoglycemia if proper measures are not taken. Prolonged exercise can also predispose to decreased glucose counter regulation. It is better for the type 1 diabetic subject to postpone the exercise session in very high (>300 mg/dl) or very low (<70 mg/dl) BG levels. Every insulin treated subject is recommended to be checked for any existing diabetic complication before the start of every exercise program. Glucose measurement with glucose meters or sometimes with Continuous Glucose Monitoring System (CGMS) must be made before, during and most importantly after the end of the exercise session. It is recommended either to reduce or suspend the previous insulin dose depending on the insulin regime or to receive extra carbohydrates before, during or after the exercise session or both. Subjects with type 1 DM may participate at almost all the competitive sports if precautions are taken. These measures must be individualized and readjusted, even empirically. In very high intensity exercise (about 80% of VO2 (max)) or when high intensity exercise follows a low intensity one, there is a tendency of the BG to increase due to excessive circulating catecholamines necessitating postexercise short acting insulin. In anaerobic or resistance exercise lactic acid is produced. This exercise type is recommended for people in whom aerobic exercise is contraindicated. These two exercise types can be combined. The incidence of hypoglycemia or hyperglycemia in specific forms of resistance exercise as well as the appropriate insulin dose adjustment are not well studied. In conclusion all exercise types are beneficial for both types of diabetes. The complete elucidation of the mechanisms of blood glucose disturbances during and after exercise in diabetes is very important for the successive outcome of various exercise programs in subjects with DM. (C) 2011 Elsevier Ireland Ltd. All rights reserved.