Physical Activity and Exercise
Exercise has many positive health and psychological benefits including physical fitness, weight management, and enhanced insulin sensitivity. It also provides opportunities for social interactions and builds self-esteem. However, exercise creates challenges for people with type 1 diabetes due to the increased risk for both hypoglycemia and hyperglycemia. During exercise, multiple hormones (insulin, glucagon, catecholamines, growth hormone, and cortisol) control fuel metabolism and create a balance between glucose uptake by exercising muscles and hepatic glucose production.[33,34] The equilibrium between insulin secretion and the counterregulatory hormones varies according to the exercise type, intensity, and duration.
Hyperglycemia results from counterregulatory hormone excess with insufficient insulin, leading to excessive hepatic glucose production and limiting increased glucose uptake into skeletal muscle. Hyperglycemia can occur before, during, and after various types of exercise. If the patient feels well, with negative or minimal urine and/or blood ketones, and there is a clear reason for the elevated blood glucose level, such as underdosing insulin at the preceding meal, it is not necessary to postpone exercise based solely on hyperglycemia. However, when people with type 1 diabetes are deprived of insulin for 12–48 h and are ketotic, exercise can worsen hyperglycemia and ketosis. Therefore, vigorous activity should be avoided in the presence of severe hyperglycemia and ketosis, especially with known insulin omission.
Physical activity increases hypoglycemia risk during and immediately following exercise, and, again, about 7–11 h postexercise. This delayed susceptibility to hypoglycemia is referred to as the "lag effect" of exercise[36,37] and is caused by muscles replenishing glycogen stores postexercise. Hypoglycemia and fear of hypoglycemia can limit participation in exercise.
Strategies should be developed to prevent and treat hypoglycemia readily. Individualization is necessary, but clinical experience suggests that it is safest for most patients to have a blood glucose level of 100 mg/dL (5.6 mmol/L) or higher prior to starting exercise. This may be achieved by reducing the prandial insulin dose for the meal/snack preceding exercise and/or increasing food intake. Some patients can avoid hypoglycemia by reducing insulin (such as by lowering pump basal rates) or by consuming additional carbohydrates during prolonged physical activity. One study in children on pumps suggested that a reduction in overnight basal insulin the night following exercise may reduce the risk of delayed exercise-induced hypoglycemia. Frequent SMBG and/or CGM use are key to exercising safely, as is ready access to carbohydrates.
Basic recommendations for physical activity are the same as those for all children and adults, independent of the diagnosis of diabetes: children should be encouraged to engage in at least 60 min of physical activity daily, and adults should be advised to perform at least 150 min/week of moderate-intensity aerobic physical activity (50–70% of maximum heart rate) or a lesser amount (60–75 min/week) of vigorous-intensity activity.[40,41] Exercise should also include resistance and flexibility training.
Individuals, particularly adults, should be assessed for cardiovascular risk and the presence of complications that might limit exercise as discussed more fully in the ADA Standards of Medical Care in Diabetes.
Exercise should be a standard recommendation as it is for individuals without diabetes; however, recommendations may need modifications due to the presence of macro- and microvascular diabetes complications. (E)
Patients of all ages (or caregivers of children) should be educated about the prevention and management of hypoglycemia that may occur during or after exercise. (E)
Patients should be advised about safe preexercise blood glucose levels (typically 100 mg/dL or higher depending on the individual and type of physical activity). (E)
Reducing the prandial insulin dose for the meal/snack preceding exercise and/or increasing food intake can be used to help raise the preexercise blood glucose level and reduce hypoglycemia. (E)
A reduction in overnight basal insulin the night following exercise may reduce the risk for delayed exercise-induced hypoglycemia. (C)
SMBG should be performed as frequently as needed (before, during, and after exercise) in order to prevent, detect, and treat hypoglycemia and hyperglycemia. (E)
Source(s) of simple carbohydrate should be readily available before, during, and after exercise to prevent and treat hypoglycemia. (E)
Diabetes Care. 2014;37(7):2034-2054. © 2014 American Diabetes Association, Inc.