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 <7.0%), even if they are slightly hyperglycemic at the time of exercise. In one study, physical working capacity in well controlled prepubertal boys was not different from non-diabetic boys matched for age, weight and physical activity patterns, even though the boys with diabetes exercised with considerably higher blood glucose concentrations (mean blood glucose 15 mmol/l at onset of exercise) (16) [B]. In line with this, cycling performances in adult males with type 1 diabetes do not differ between glucose levels clamped at euglycemia vs. hyperglycemia (12 mmol/L, 220 mg/dL) (17). In contrast, aerobic capacity is lower and the fatigue rate is higher in youth with type 1 diabetes when glycemic control is less than optimal (i.e. HbA1c >7.5 %) (9) [B]. Moreover, performance in sports like hockey, soccer and sailing where a certain amount of cognitive function and precision is necessary may be better performed during normoglycemia (E) compared with hyperglycemia, although studies have yet been conducted to address this hypothesis. However, cognitive performance has been shown to be slower in youth with diabetes when their blood glucose is either hypo- or hyperglycemic (18) [C] When regular (soluble) insulin has been injected prior to exercise, the most likely time for hypoglycemia will be 2-3h after injection and the high risk time after rapid-acting analog insulin is between 40 and 90 minutes (19) [B]. We have found no studies on the timing of basal insulins (NPH, glargine ordetemir) 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 the next day 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 (20). If extra carbohydrate is necessary for a short duration activity, then it may be useful to have "fast acting" carbohydrates in a beverage form. An isotonic beverage containing 6% simple sugar (i.e., sucrose, fructose, dextrose) 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 (20). Check the glucose content of sport drinks, as 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 (20), depending upon type of activity. See Table 2. The requirements will be lower if the premeal bolus for the meal before the exercise is lowered or the exercise is performed several hours after the bolus dose has been given. Extra carbohydrates together with adjustments of insulin doses are especially important when the activity is of longer duration than 60 min (21) [E]. 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 after the activity (carbohydrate reloading). Short duration and high intensity anaerobic activities (such as weight lifting, sprints, diving and baseball) may not require carbohydrate intake 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 intake to limit post-exercise hypoglycemia. However, reductions in basal insulin, low-glycemic-index snacks (with no bolus), or reduced boluses at post-exercise 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 (22) [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 (23) [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 (24) [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 (25) [C]. An intense 30-min period of exercise did not increase the absorption rate of glargine in adults with type 1 diabetes (26) [C]. 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 blood glucose. Morning activity, done before insulin administration, may not result in hypoglycemia as circulating insulin levels are typically low and glucose counterregulatory hormones may be high (91) [C]. 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 for consistency in blood glucose management. Some groups of schoolchildren and teenagers with diabetes have been found to be more physically active than their nondiabetic friends (27) [C]. Regular and accustomed exercise is easier to manage because it is part of the daily routine. However, adjustments may still 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 afterwards. Advice from the diabetes team will be general in the first instance, but accurate record keeping will allow much more individualised 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 that good metabolic control maximizes exercise (9) [B]. An inverse relationship was observed between HbA1 level and the maximal work load in a study in diabetic adolescents (28) [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 (29) [B]. The management of diabetes may vary according to the phase of training so 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 (30) and increased activation of non-insulin sensitive glucose transporters (GLUT-4) (31). Insulin sensitivity was similar directly and 15 hours after exercise but decreased to near untrained levels after 5 days in non-diabetic adults (32). During and immediately after exercise and from 7–11 hours in recovery, the insulin sensitivity is elevated in adolescents with type 1 diabetes (33) [B]. In practical life, exercise for >1 hour can lead to increased insulin sensitivity and therefore an increased risk for hypoglycemia for at least 24 hours (33) [B,E]. This means that adolescents who only exercise on occasion can have real difficulties in managing their basal insulins [E]. If hypoglycemia is frequent, then it may be better to exercise every other day rather than a few days in a row every week, if possible. If not, a strategy for altering basal insulins to cope with the widely varying insulin sensitivity is needed. Younger children more often exercise rather well every day to some extent, which results in less post-exercise 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 post-exercise 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 to the post-exercise meal increases the glucose uptake and enhances glycogen resynthesis in healthy individuals (34) [C]. Added proteins will also stimulate the muscle-recovery post exercise. It is well beyond the scope of this chapter to offer sport-specific training advice but such information is readily available—see: Diabetes Exercise & 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: E.g. where a mixed insulin is given before breakfast, then a split-evening insulin with rapid analog before the 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 or at regimens or insulin regimens greater for training and pre-exercise bolus and basal rates can be reduced before, during and after exercise to help increase hepatic glucose production and limit hypoglycemia The choice of insulin regimen is influenced by many different the of various insulins and and in the should be influenced by the of the sport. is no that being to reduce the training day of hours control of blood glucose much more with the potential to periods in the day and being to the appropriate bolus insulin doses [C]. In the autonomic and counter-regulatory response to hypoglycemia the following day has been shown to be by repeated of low or moderate intensity exercise [B]. The same is likely to be for Glucose requirements for stable glucose levels in adolescents with diabetes are elevated during and shortly after exercise, as well as from 7–11 h after exercise (33) [B]. In repeated of hypoglycaemia in a results in an counter-regulatory response to exercise and increases the risk for hypoglycemia. two to three times more glucose may be to maintain euglycemia during exercise following a to hypoglycemia [B]. In studies of diabetic adolescents who their insulin dose and then performed minutes on a hypoglycemia if their blood glucose was less than mmol/l In the same study, it was that was frequently to blood glucose to normal In study [B], of children with type 1 diabetes blood glucose levels drop mmol/l during 60 minutes of moderate cycling performed in the when insulin was for the activity. additional carbohydrate glucose at a rate that carbohydrate during exercise of carbohydrate body the drop in blood glucose during exercise be prevented [B]. 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]. hypoglycemia with a rise in of approximately 3–4 approximately g of glucose is for a 30 child and 15 g for a See the hypoglycemia chapter for further advice and or activity all the adults 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 together on they should in groups of at least so that 2 can other if they need to adult to the of an or hypoglycemia. Glucose glucose or some of sugar should be by young people who exercise at a kept within a distance of the activity. See Table for further advice on to avoid hypoglycemia when can occur several hours after exercise, especially when this has been and of moderate or high intensity [C]. This is due to the effect of increased insulin sensitivity and delay in liver and muscle glycogen stores. A of exercise can increase glucose skeletal muscle for at least hours in non-diabetic and diabetic subjects (30) [B]. In a controlled study, as many a event on the after an exercise day compared to the after a day the basal insulin was not 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 (29) [B]. and adjustments are In a group of young people a sport of at least hours of a lower HbA1c (27) [C]. In one study, with type 1 diabetes were to on for several hours without hypoglycemia when the premeal dose by compared to only 90 minutes if the dose was reduced by [C]. Some people that their premeal insulin dose may cause an rise in their blood glucose which their performance [E]. In such a it is better to on extra carbohydrate intake rather than dose reduction for best See for on adjustments of pre-exercise bolus doses in to avoid hypoglycemia. is a greater need for reduction of rapid-acting insulin when the dose is given within 1 hour of the exercise, while the need of reduction is greater for exercise hours when regular insulin. (19) [B]. For evening exercise, it may be to reduce the rapid analog before the evening meal by to as well as taking of acting carbohydrate before the activity. Advice insulin a reduction in insulin or basal rate in pump or reductions in and/or extra low glycemic snacks following the activity is or activities such as sports 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 For certain of exercise it may be appropriate to prior to the of the activity and remain for up to during an event. In these patients may require a bolus of the basal insulin while if to reduce any resulting post-exercise a of the basal insulin effect during the exercise, the pump to be at least 90 minutes before the exercise but many that the pump should not be for more than The option may be to a basal rate 90 minutes before the activity, lasting the of exercise. if the pump is during exercise, hypoglycemia can still occur for several hours after the of the activity [C]. a short period of intense exercise VO2 marked responses lead to hyperglycemia which for approximately 2 hours post-exercise in adults with type 1 [B]. when pre-exercise plasma glucose was there a post-exercise hyperglycemia which for 2 hours in pump patients [C]. This may be 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]. In of poor control or any exercise is likely to be because of the effect of action of the counter-regulatory In one study in patients exercising with a blood glucose of > mmol/l and experienced a rise in blood glucose 40 minutes [B]. The rapid production of with impaired muscle glucose uptake will lead not only to but may and it is important for families to be not in exercise if blood glucose is high and or are in the or the level of in blood is > It is a that no insulin is 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 [E]. During of blood than > mmol/l is in children with diabetes 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 on the of the child and the activity performed as well as the level of circulating insulin (19) [B]. to carbohydrate of body hour 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 (20). It is adolescents and young adults the effect of upon the ability to to exercise and blood glucose on and the glucose in subjects with diabetes by gluconeogenesis not 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 due to may performance [C]. In both can often be by drinks, but if is a risk, sugar fluids should also be intake should

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