Introduction
During exercise, whole-body oxygen consumption may increase by as much as 20-fold, and even greater increases may occur in the working muscles. To meet its energy needs under these circumstances, skeletal muscle uses, at a greatly increased rate, its own stores of glycogen and triglycerides, as well as free fatty acids derived from the breakdown of adipose tissue triglycerides and glucose released from the liver. To preserve central nervous system function, blood glucose levels are remarkably well-maintained during exercise. Hypoglycemia during exercise rarely occurs in nondiabetic individuals. The metabolic adjustments that preserve normoglycemia during exercise are in large part hormonally mediated. A decrease in plasma insulin and the presence of glucagon appear to be necessary for the early increase in hepatic glucose production during exercise, and during prolonged exercise increases in plasma glucagon and catecholamines appear to play a key role. These hormonal adaptations are essentially lost in insulin-deficient patients with Type 1 diabetes. As a consequence, when such individuals have too little insulin in their circulation due to inadequate therapy, an excessive release of counter-insulin hormones during exercise may increase already high levels of glucose and ketone bodies and can even precipitate diabetic ketoacidosis. Conversely, the presence of high levels of insulin, due to exogenous insulin administration, can attenuate or even prevent the increased mobilization of glucose and other substrates induced by exercise and hypoglycemia may ensue. Similar concerns exist in patients with type 2 diabetes on insulin or sulfonylurea therapy; however, in general hypoglycemia during exercise tends to be less of a problem in this population. Indeed, in patients with type 2 diabetes, exercise may improve insulin sensitivity and assist in diminishing elevated blood glucose levels into the normal range.
The purpose of this position paper is to update and crystallize current thinking on the role of exercise in patients with types 1 and 2 diabetes. With the publication of new clinical reviews, it is becoming increasingly clear that exercise may be a therapeutic tool in a variety of patients with, or at risk for diabetes, but that like any therapy its effects must be thoroughly understood. From a practical point of view, this means that the diabetes health-care team will be required to understand how to analyze the risks and benefits of exercise in a given patient. Furthermore, the team, consisting of, but not limited to, the physician, nurse, dietitian, mental health professional, and the patient, will benefit from working with an individual with knowledge and training in exercise physiology. Finally, it has also become clear that it will be the role of this team to educate primary care physicians and others involved in the care of a given patient.
Cite this: Diabetes Mellitus and Exercise - Medscape - Dec 01, 1997.
