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 hemoglobin A1c (HbA1c) levels (1–3) (B), the benefits of exercise go far wider: weight control, reduced cardiovascular risk, and an improved sense of well-being (4) (B). Postmeal 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 (5) (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 that 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 Fig. 1, non-diabetic individuals have a reduction in insulin secretion and an increase in glucose counter-regulatory 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 (4) (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 counter-regulation, making normal fuel regulation nearly impossible. Hypoglycemia commonly occurs during exercise when insulin is administered prior to the start of the activity. In real life, young people with diabetes have variable blood glucose responses to exercise. The blood glucose response to 60 min of intermittent exercise is somewhat reproducible if the timing of exercise and the amount of insulin and the pre-exercise meal remain consistent (6) (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 (7) (B). Young people with type 1 diabetes have been found to have decreased aerobic capacity as measured by VO2 max compared with non-diabetic control subjects (8) (B). Total body insulin-mediated glucose metabolism in adolescents correlates with the degree of glycemic control as assessed by the level of glycosylated hemoglobin (9) (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 the 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 min 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 with continuous moderate-intensity exercise, both during and after the physical activity in young adults (10) (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 h after the exercise (11) (B). However, typical team games may last up to 90 min, 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 because 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 because of the release of the hormones adrenaline and glucagon. This rise in blood glucose is usually transient, lasting typically 30–60 min, and can be followed by hypoglycemia in the hours after finishing the exercise. Aerobic activities tend to lower blood glucose both during (usually within 20–60 min after the onset) and after the exercise (4) (B). Where control is poor and preexercise 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 (12) (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 (13) (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 (14). When regular (soluble) insulin has been injected prior to exercise, the most likely time for hypoglycemia will be 2–3 h after injection, and the high-risk time after rapid analogue insulin is between 40 and 90 min (15) (B). We have found no studies on the timing of basal insulins (NPH, glargine, or detemir) and exercise. When playing morning or all-day tournaments, a long-acting basal insulin given once daily in the evening can be substituted for one with shorter action (NPH) to reduce the basal insulin effect while exercising (E). A meal containing carbohydrates (CHO), fats, and protein should be consumed roughly 3–4 h prior to competition to allow for digestion and for a maximizing of endogenous energy stores. This is especially important for longer-duration activities. Glycogen stores can be enhanced with a carbohydrate beverage (1–2 g CHO/kg) approximately 1 h prior; this also helps to supplement energy stores and provide adequate fluids for hydration (16). If extra carbohydrate is necessary for short duration activity, then it may be useful to have 'fast-acting' carbohydrates such as glucose drinks. An isotonic beverage containing 6% simple sugar (i.e., sucrose, fructose, and glucose) provides optimal absorption compared with other more concentrated beverages with more than 8% glucose such as juice or carbonated drinks that delay gastric absorption and cause stomach upset (16). Check the glucose content of sport drinks, some contain >8% glucose. The amount of carbohydrate should be matched as closely as possible to the amount of carbohydrate utilized during exercise if a reduction in insulin is not performed. In general, approximately 1.0–1.5 g CHO/kg body weight/h should be consumed during exercise performed during peak insulin action in young adults with diabetes (16) (Table 2). Because insulin sensitivity remains elevated for hours postexercise, carbohydrate stores must be replenished quickly to lower the risk of hypoglycemia during the first few hours postactivity (carbohydrate reloading). Short duration and high-intensity anaerobic activities (such as weight lifting, sprints, diving, and baseball) may not require carbohydrate prior to the activity, but may produce a delayed drop in blood sugar. For activities of these types, extra carbohydrate after the activity is often the best option to prevent hypoglycemia (E). Longer-duration, lower intensity aerobic activities such as soccer (often described as a mixture between aerobic and anaerobic exercise), cycling, jogging, and swimming will require extra carbohydrate before, possibly during, and often after the activity (E). Currently, no evidence-based guidelines exist on the amount and timing of increased carbohydrate to limit postexercise hypoglycemia. However, reductions in basal insulin, low glycemic index snacks (with no bolus), or reduced boluses at postexercise meals will usually reduce the problem (E). A snack of complex carbohydrate, fat, and protein at bedtime may limit nocturnal hypoglycemia caused by daytime exercise (17) (B). Choice of injection site: When an extremity (arm or leg) has been injected with insulin and is then exercised vigorously, the increased blood flow to the limb is likely to result in more rapid absorption and metabolic effect of the insulin (18) (B). This may be especially marked if the injection site is hypertrophied. Thus, a cyclist may achieve more consistent response by choosing to inject in an arm or the abdomen rather than a leg before an event. Ambient temperature: High temperature will increase insulin absorption and low temperature the converse (19) (B). The latter may be a consideration in long-distance swimming. Most absorption studies were done with regular insulin. The effect is less pronounced with rapid-acting analogues (20) (C). An intense 30-min period of exercise did not increase the absorption rate of glargine in adults with type 1 diabetes (21). Heat also places additional stress on the cardiovascular system, resulting in greater energy expenditure and potential for a faster drop in blood glucose levels. Using more muscles produces a greater drop in blood glucose, and weight-bearing activities tend to use more energy than non-weight-bearing activities. Patients frequently report that the drop in blood glucose may be less with regular conditioning and familiarity with the sport, although no experimental evidence exists that tests this hypothesis. The adrenal response will raise the blood glucose. Morning activity, done before insulin administration, may not result in hypoglycemia as circulating insulin levels are typically low and glucose counter-regulatory hormones may be high. Indeed, severe hyperglycemia may occur with vigorous exercise in these circumstances, even precipitating ketoacidosis. Daily physical activities should be a part of the normal routine for both health benefits and consistency in blood glucose management. Some groups of schoolchildren and teenagers with diabetes have been found to be more physically active than their non-diabetic friends (22) (C). Regular and accustomed exercise is easier to manage because it is part of the routine, but adjustments may also be necessary for sporadic extra physical activity. Whatever level of involvement in exercise and sport that a child or adolescent with diabetes adopts, it is good practice that careful notes are kept of what they do (timing and intensity of physical activity), what carbohydrate has been taken, and the blood glucose response before, during, and afterward. Advice from the diabetes team will be general in the first instance, but accurate record keeping will allow much more individualized and fruitful consultation (E). Where exercise is performed regularly, insulin sensitivity is generally enhanced. A positive association between glycemic control (i.e., HbA1c) and aerobic fitness or reported physical activity exists in youth with type 1 diabetes, suggesting that either increased aerobic capacity may improve glycemic control or good metabolic control maximizes exercise (8) (B). An inverse relationship was observed between HbA1c level and the maximal work load in a study in diabetic adolescents (23) (B). The lack of evidence on improving HbA1c with exercise may be related to a tendency to over-reduce insulin doses and consume excessive carbohydrate in an effort to avoid hypoglycemia (24) (B). The management of diabetes may vary according to the phase of training so that when endurance is being built with long moderate-intensity work, the insulin regimen and additional carbohydrate may be quite different from that required when the concentration is upon power and high-intensity training. See the Duration and intensity section above for more detail on the possible effect of short, high-intensity work on glycemia. Exercise causes enhanced muscle insulin sensitivity (25) and increased activation of non-insulin-sensitive glucose transporters (GLUT-4) (26) (C). Insulin sensitivity was similar directly and 15 h after exercise but decreased to near untrained levels after 5 d in non-diabetic adults (27). During and immediately after exercise and from 7–11 h in recovery, the insulin sensitivity is elevated in adolescents with type 1 diabetes (28) (B). In practical life, exercise for >1 h can lead to increased insulin sensitivity for up to 48 h. This means that adolescents who only exercise intermittently can have real difficulties in managing their basal insulins (E). It is therefore better to exercise at least every other day if possible. If not, a strategy for altering basal insulins to cope with the widely varying insulin sensitivity is needed. Younger children most often exercise rather well every day to some extent, which results in less postexercise fluctuations in blood glucose (E). Meals with high content of carbohydrates should be consumed shortly after the exercise event to take advantage of the period of heightened insulin sensitivity to help replenish glycogen content and limit postexercise hypoglycemia. However, the insulin dose will need to be reduced (in relation to the normal insulin-to-carbohydrate ratio for the individual) to avoid hypoglycemia. Adding protein will enhance glycogen resynthesis (29) (C). It is well beyond the scope of this chapter to offer sport-specific training advice, but such information is readily available – see: Diabetes Exercise and Sports Association (www.diabetes-exercise.org), an international organization that provides guidance and networking between novices, health professionals, and experienced diabetic athletes. www.runsweet.com where a combination of contributions from sportsmen and sportswomen are interspersed with expert advice. For most children and adolescents, the choice of insulin regimen will not be influenced heavily by their exercise habits. However, for some who are regularly active, it is likely that either multiple daily injections or insulin pump therapy be considered to allow for manipulations in insulin delivery prior to and following the activity. Twice-daily injections: It may be difficult to maintain very strict blood glucose control on these regimens, especially with different levels of exercise throughout the week, but the essential requirements of taking various forms of carbohydrate before, during, and after exercise may be even more important than for more adjustable regimens. Three-injections insulin regimen: For example, where a mixed insulin is given before breakfast, then a split-evening insulin with rapid analogue before evening meal and a longer-acting insulin at bedtime. Again this regimen must be accompanied by appropriate carbohydrate advice for moderate exercise, e.g., dancing or swimming two or three evenings per week or at weekends. Multi-injection regimens or insulin pumps: This regimen affords greater flexibility for serious training and competitive events. Both preexercise bolus and basal rates can be reduced before, during, and after exercise to help increase hepatic glucose production and limit hypoglycemia (see below). The choice of insulin regimen is always influenced by many different factors including the availability of various insulins (and pumps), professional and personal expertise, and in the ideal world should be influenced by the nature of the sport. There is no doubt that being able to reduce the training day into manageable 'chunks' of 4–6 h makes control of blood glucose much more straightforward with the potential to move training/competitive periods around in the day and being able to adjust the appropriate bolus (and perhaps basal) insulin doses (30) (C). In adults, the autonomic and counter-regulatory response to hypoglycemia the following day has been shown to be blunted by repeated low- or moderate-intensity exercise (31) (B). The same phenomenon is likely to be true for children. Glucose requirements to maintain stable glucose levels in adolescents with diabetes are elevated during and shortly after exercise as well as from 7–11 h after exercise (28) (B). In adults, repeated episodes of hypoglycemia in a sedentary state result in an attenuated counter-regulatory response to subsequent exercise and increase the risk for hypoglycemia. Hence, two to three times more exogenous glucose may be needed to maintain euglycemia during exercise following a previous exposure to hypoglycemia (32) (B). In laboratory studies of diabetic adolescents who received their usual insulin dose and then performed 75-min walking on a treadmill, 86% had hypoglycemia if their starting blood glucose was <6.6 mmol/L (120 mg/dL). In the same study, it was noted that 15 g CHO was frequently insufficient to restore blood glucose to normal (33) (A). In another study (34) (B), 45% of children with type 1 diabetes had blood glucose levels drop below 4.0 mmol/L (72 during 60 min of moderate cycling performed in the additional carbohydrate glucose at a rate that carbohydrate during exercise g CHO/kg body the drop in blood glucose during exercise be If a child with diabetes is during exercise with and of hypoglycemia, glucose or other of carbohydrate should be given as for of hypoglycemia, even if blood glucose be measured to hypoglycemia (E). or activity all the adults (and also should be to the of hypoglycemia. guidance should be given that no person with diabetes should exercise or go or not to have regular snacks when they are A is that if young people with diabetes are on they should in groups of at least so that two can other if they need to to the of an or hypoglycemia. Glucose glucose or some of sugar should always be by young people who exercise at a kept within a of the activity. Hypoglycemia can occur hours after exercise especially when this has been and of moderate or high intensity (C). This is because of the effect of increased insulin sensitivity and delay in liver and muscle glycogen stores. A of exercise can increase glucose into skeletal muscle for at least h postexercise in non-diabetic and diabetic subjects (25) (B). In a controlled study, as many had a event on the after an exercise day compared with the after a sedentary day the basal insulin was not (A). glucose may be a valuable for the blood glucose response and hypoglycemia risk during and after exercise athletes may be to reduce their insulin doses much to avoid hypoglycemia, and their metabolic control may as a result (24) (B). and adjustments are In a of young people a competitive sport of at least h of exercise per week had a lower HbA1c (22) (C). In one study, with type 1 diabetes were able to on for hours hypoglycemia when the dose by compared with only 90 min if the dose was reduced by (C). Some people that their insulin dose may cause an rise in their blood glucose, which their performance (E). In such a it is better to on extra carbohydrate rather than dose reduction for best See Table for on adjustments of preexercise bolus There is a greater need for reduction of rapid-acting insulin when the dose is given within 1 h of the exercise, while the need of reduction is greater for exercise h when regular insulin. (15) (B). For evening exercise, it may be to reduce the rapid analogue before the evening meal by as well as taking g of carbohydrate before the activity. Advice insulin a reduction in insulin or basal rate in pump or reductions in subsequent and/or extra index snacks following the activity is or activities such as long-distance a reduction of long-acting insulin the before and on the day of the activity or a reduction in the basal insulin throughout the day and the following the activity. High and may be more likely to raise because of (E). For of exercise it may be appropriate to prior to the start of the activity and remain for up to h during an event. In these patients may require a bolus (i.e., of the basal insulin while if to reduce any resulting postexercise a of the basal insulin effect during the exercise, the pump to be at least 90 min before starting the exercise but many that the pump should not be for more than 2 h. The option may be to move to a basal rate 90 min before the activity the of exercise. if the pump is during exercise, hypoglycemia can occur for hours after the of the activity (C). a short period of intense exercise VO2 marked responses lead to which for approximately 2 h postexercise in adults with type 1 diabetes (B). when pre-exercise plasma glucose was there a which for 2 h in pump patients (C). This may be exaggerated if the pump has been during exercise. The rise in blood glucose may be prevented by a additional dose of rapid-acting insulin at or immediately after the exercise is (E). insulin regimen to activity. the reductions in insulin before exercise. type and amount of carbohydrate required for activities. risk of hypoglycemia and reduction in insulin. In of poor control or intense exercise is likely to be because of the effect of action of the counter-regulatory In one study in adults, patients with a blood glucose of mmol/L and experienced a further rise in blood glucose during 40 min of exercise (B). The rapid production of with impaired muscle glucose uptake will not only lead to but also may and Thus, it is important for families to be not in strenuous exercise if blood glucose is high and or are in the or mmol/L of in It is a that no insulin is needed when exercise is to be This be a insulin is being by a long-acting and under provides additional information to (E). This is for rapid and of levels and is when available (E). During of blood than mmol/L is in children with diabetes and exercise is and should be if preexercise blood glucose levels are high mmol/L or with approximately or of daily dose including all meal bolus doses and basal rate in and exercise have (E). When insulin is not reduced to for exercise, it is usually necessary to consume extra carbohydrate in to avoid hypoglycemia. This is dependent upon type and duration of activity. The amount of carbohydrate needed on the of the child and the activity performed as well as the level of circulating insulin (15) (B). to g CHO/kg body of strenuous exercise may be needed. carbohydrate for on duration of activity and body are found in a by Gary Insulin by and and for youth in a by and (16). It is adolescents and young adults the effect of upon the ability to to exercise and blood glucose. the glucose in subjects with diabetes by gluconeogenesis not and hypoglycemia more likely and is best when in exercise, especially as may also While not to people with diabetes, the risk of should be in much be kept upon glucose a in body because of may performance (C). In both can often be by drinks, but if is a risk, fluids should also be should and such that there is no in body weight preexercise may need to be as as in adolescents exercising in and (B). up to g CHO/kg body of strenuous or longer-duration exercise when circulating insulin levels are high. so hypoglycemia is more is a risk fluids also are glucose is for the active child with diabetes so that in glycemic responses can be should notes of their blood glucose, the duration and intensity of exercise as well as the to maintain glucose in the normal of glucose should be before, during, and after the of exercise with to the of in glycemia. hours after exercise and before is on where strenuous activities occur as nocturnal hypoglycemia is It remains bedtime levels nocturnal hypoglycemia, and are difficult after exercise. In one study, a bedtime blood glucose of mmol/L risk for nocturnal hypoglycemia while another study found no for nocturnal hypoglycemia risk after exercise in the (A). It remains to be seen what the practical impact of continuous glucose will should be when in (B). glucose may more accurate at high In circumstances where control is to the e.g., on a long further with the only being accurate between In such as keeping a and of to the body will usually prevent should be at

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