Exercise in children and adolescents with diabetes

In the 1950s, Joslin proposed that exercise is the third essential component in blood glucose regulation for persons with type 1 diabetes, after insulin and dietary management. Although most studies have shown little impact upon HbA1c levels (1–3) B, a cross-sectional analysis of data on a larger group showed that the frequency of regular physical activity was associated with lower HbA1c without increasing the risk of severe hypoglycaemia (4) C. The benefits of exercise go far wider: weight control, reduced cardiovascular risk, and an improved sense of well-being (5) B. Post-meal exercise can be a valuable way to minimize postprandial glycemic spikes E. For some, participation in physical activity is somewhat sporadic and related to leisure, school or work. For others, daily exercise is a part of an overall training or conditioning program. Children and adolescents with diabetes should derive many of the same health and leisure benefits as adults and should be allowed to participate with equal opportunities and with equal safety. Diabetes should not limit the ability to excel in a chosen sport. Many famous athletes have proved this e.g. Sir Steve Redgrave the five times Olympic Gold Medal winning rower, Gary Hall the US Olympic Gold Medal swimmer at Athens, Wasim Akram is a Pakistani cricketer at the international level, Major League baseball player Jason Johnson, Ironman Triathlete Bill Carlson and female pro golfer Mimmi Hjorth. The topic most commonly discussed with families with regard to exercise is avoidance of hypoglycemia, but prevention of acute hyperglycemia/ketoacidosis may become a concern as well (6) C. While this chapter is intended to address the issue of blood glucose regulation during various forms of sports and exercise, it is important for diabetes professionals and parents to appreciate that the demands of day to day physical activity will also have to be considered if a young person is going to participate in any activity, which for them is unusually strenuous or prolonged. Before considering the situation in Type-1 diabetes, it is useful to understand the physiological response to moderate intensity aerobic exercise in the non-diabetic individual. As shown in Figure 1, non diabetic individuals have a reduction in insulin secretion and an increase in glucose counterregulatory hormones that facilitate an increase in liver glucose production which matches skeletal muscle glucose uptake during exercise. As a result of this precise autonomic and endocrine regulation, blood glucose levels remain stable under most exercise conditions (5) B. Physiologic responses to exercise in the diabetic and non-diabetic individual. square brackets denote plasma concentration. In type 1 diabetes, the pancreas does not regulate insulin levels in response to exercise and there may be impaired glucose counterregulation, making normal fuel regulation nearly impossible. As a result, hypoglycemia commonly occurs during or soon after exercise. In real life, young people with diabetes have variable blood glucose responses to exercise. The blood glucose response to 60 minutes of intermittent exercise is somewhat reproducible within a child if the timing of exercise, the amount of insulin and the pre-exercise meal remain consistent (7) B. Glucose production in healthy control subjects increases with exercise intensity and can be entirely attributed to increases in net hepatic glycogenolysis. In contrast, moderately controlled type 1 diabetic subjects exhibit increased rates of glucose production both at rest and during exercise, which can be entirely accounted for by increased gluconeogenesis (8) B. Young people with T1D have been found to have decreased aerobic capacity as measured by VO2 max, compared to nondiabetic control subjects (9) B. Total-body insulin-mediated glucose metabolism in adolescents correlates with the degree of glycemic control as assessed by the level of glycosylated haemoglobin (10) B. However, even in the same individual, it is possible for the blood glucose to be increased, decreased or unchanged by exercise dependent upon circumstances as indicated in Table 1. It is especially important to plan for long duration or intense aerobic exercise, or else hypoglycemia is almost inevitable. Nearly all forms of activity lasting > 30 minutes will be likely to require some adjustment to food and/or insulin. Most team and field sports and also spontaneous play in children are characterized by repeated bouts of intensive activity interrupting longer periods of low to moderate intensity activity or rest. This type of activity has been shown to produce a lesser fall in blood glucose levels compared to continuous moderate intensity exercise, both during and after the physical activity in young adults. (11) B. The repeated bouts of high-intensity exercise stimulated higher levels of noradrenaline that increased blood glucose levels. Moderate-intensity exercise (40% of VO2 max) followed by an intense cycling sprint at maximal intensity prevented a further decline in blood glucose for at least 2 hours after the exercise (12) B. However, typical team games may last up to 90 minutes and the results may not be applicable to this length of physical activity. Furthermore, the authors were unable to explain why the short sprint countered a fall in glucose levels for so long since the rise in catecholamines following the intense exercise was very short-lived. (See also ‘Type of Activity’). Anaerobic efforts last only a short time (sometimes only seconds) but may increase the blood glucose level dramatically due to the release of the hormones adrenaline and glucagon. This rise in blood glucose is usually transient, lasting typically 30–60 minutes, and can be followed by hypoglycaemia in the hours after finishing the exercise. Aerobic activities tend to lower blood glucose both during (usually within 20–60 minutes after the onset) and after the exercise (5) B. Where control is poor and pre-exercise blood glucose level is high, circulating insulin levels may be inadequate and the effect of counter-regulatory hormones will be exaggerated, leading to a higher likelihood of ketosis E. High blood glucose has been found to reduce the secretion of beta-endorphins during exercise, which has been associated with an increased rating of perceived exertion (RPE) during leg exercise (13) B. In fact, even baseline beta-endorphin levels were reduced in the diabetic subjects irrespective of blood glucose, and thus the resultant reduced tolerance of discomfort may compromise exercise performance in individuals with diabetes. Similarly, increases were found in RPE in adolescents with diabetes doing whole-body exercise (14) B, but the authors indicate that the higher response is thought to be mainly a function of the lower peak mechanical power output often seen in these patients (15). Children with diabetes can have normal aerobic and endurance capacity if good glycemic control is achieved (HbA1c mmol/l and a rise in blood glucose minutes B. 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