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Chapter 6 Aerobic Exercise Rx for Type 1 Diabetes and Latent Autoimmune Diabetes in Adults

Many health benefits of regular physical activity are available to individuals with type 1 diabetes (T1D) or latent autoimmune diabetes in adults (LADA), regardless of their age at onset. For example, regular exercise lowers blood pressure, lipid levels, body weight, cardiovascular and mortality risk, and risk of complications while raising cardiorespiratory fitness levels, muscular strength, quality of life, and sense of well-being (Moy 1993, Laaksonen 2000, Costacou 2007, Herbst 2007, Heyman 2007, Bishop 2009, Conway 2009, Trigona 2010, D’Hooge 2011, Maahs 2011). People with T1D can have lifestyle habits (including sedentary behaviors) that lead to greater insulin resistance and “double diabetes,” with symptoms of both T1D and type 2 diabetes (T2D) (Purnell 1998, Orchard 2003, Kilpatrick 2007). Although an acute bout of exercise improves insulin sensitivity in those with T1D as well, little or no improvement in glucose control has been demonstrated after regular exercise training, even though insulin doses generally decrease (Ebeling 1995, Roberts 2002, Ramalho 2006).

Case in Point: Aerobic Exercise Rx for a Young Adult with T1D

MF is a 20-year-old woman currently attending college who has had T1D since the age of 16 years. Although she has achieved reasonable control over her blood glucose levels—even though she is out of the “honeymoon period”—she has gained around 15 lb and is taking higher insulin doses than ever before to keep control over her daily glucose fluctuations. Her college classes are stressful for her this semester, and she has slacked off on doing any regular physical activity (although she rides her bike to classes and walks around a lot). Her goals are to lose the extra 15 lb she gained (her best weight is around 130 lb) and get her A1C value back below 6.5% (ideally no higher than 6.0%, though).

Resting Measurements

Height: 66 inches

Weight: 145 lb

BMI: 23.4 (in a “normal” range, but heavy for her)

Heart rate: 82 beats per minute (bpm)

Blood pressure: 125/70 mmHg

Fasting Labs

Plasma glucose: Variable (65–285 mg/dl, controlled with insulin)

A1C: 6.9%

Cholesterol: Not tested recently but has always been good in the past

Medications

Basal-bolus insulin regimen: 20 units of insulin glargine at bedtime, insulin lispro for meals, snacks, and corrections (usually 1–6 units per injection, based on carbohydrate intake)

Questions to Consider

1. What type of aerobic exercise should MF start doing to reach her goals?

2. What would be an appropriate exercise Rx for her with regard to exercise intensity, frequency, and duration?

3. How should her exercise training progress over time?

4. What precautions should MF take, and does she have any exercise limitations?

(Continued)

BENEFICIAL EFFECTS OF AEROBIC EXERCISE

Physical activity in the form of aerobic exercise should be included as part of the diabetes self-management program for individuals with T1D. Throughout life such individuals are fully capable of and gain many health benefits from engaging in a physical fitness plan (Colberg 2009).

Health Benefits of Regular Activity

Appropriate diabetes regimen changes must be made if improved blood glucose management is an expected outcome of regular physical activity by these individuals. Although regular exercise may not necessarily improve overall glycemic management, it still confers protective effects for individuals with T1D of all ages. Sedentary behavior has been associated with poor glycemic management in both adult and pediatric populations of T1D, even though regular exercise training has not been shown to improve glycemic control in most studies, likely due to the difficulty associated with balancing out appropriate insulin changes and carbohydrate adjustments for exercise (Ebeling 1995, Roberts 2002, Ramalho 2006). Nonetheless, a recent study showed that children with T1D exercising more than two times weekly significantly improved their A1C levels and lipid profiles, suggesting that being regularly active for long periods (60 min at a time or more) is likely beneficial and should be recommended (Aouadi 2011).

In addition to the potential health benefits of regular activity on blood pressure, lipid levels, body weight, and risk of complications (Moy 1993, Laaksonen 2000, Costacou 2007, Herbst 2007, Heyman 2007, Bishop 2009, Conway 2009, Trigona 2010, D’Hooge 2011, Maahs 2011), requirements for lower insulin doses that usually result from regular exercise participation are indicative of improved insulin sensitivity and—regardless of changes in glycemic levels—significantly reduce risk of all cardiovascular conditions (Trigona 2010, Seeger 2011). Youth with T1D present early signs of atherosclerosis, as well as low physical activity levels and levels of cardiorespiratory fitness, but endothelial function can be enhanced by engaging >60 min of daily moderate- to vigorous-intensity physical activity (Trigona 2010). Moreover, physical activity can offset some of the potentially negative impact of engaging in more sedentary pursuits: the glycemic impact of greater computer use on metabolic control in individuals with T1D is apparently not related to age, diabetes duration, television watching, or computer use, but rather independently and negatively related to the weekly hours spent on physical exercise (Benevento 2010).

Regular exercise even promotes longevity in people with T1D. One study reported that the 7-year mortality rate in T1D is 50% lower in individuals doing the equivalent of ~7 h a week of brisk walking (i.e., expenditure of ~2,000 kilocalories weekly) compared with <1,000 kilocalories (Moy 1993). The estimated increase in longevity resulting from regular exercise is ~10 years, which exactly counterbalances the number of years that diabetes potentially can shorten a person’s life.

Cardiorespiratory Fitness

Some, but not all, individuals with T1D have the same aerobic capacity as similar-age people without diabetes. For instance, despite having a lower anaerobic threshold and lung capacity, the aerobic capacity in people with T1D doing programmed exercise has been reported to be similar to that of normal athletes (Komatsu 2010). It appears, however, that poor glycemic control impairs pulmonary, cardiac, and vascular responses to exercise (Baldi 2010b). Highly trained individuals with T1D in one study were able to achieve the same cardiopulmonary exercise responses as trained subjects without diabetes, but these responses were reduced by poor glycemic control (i.e., A1C >7.0%) (Baldi 2010a).

Mitochondrial oxidative capacity also depends on glycemic control in untrained women with T1D, although it may not be lower than in untrained healthy women (Item 2011). Others have reported that both sex and diabetes control are significantly associated with cardiorespiratory fitness, with both women and anyone with poorer glycemic control exhibiting a lower level of fitness. At this point, it is not fully clear whether reduced fitness in children and others with T1D is attributable to lower physical activity levels or to physiological changes resulting from diabetes itself (Williams 2011), although exercise training in children improves their overall physical fitness (Seeger 2011).

AEROBIC EXERCISE RESPONSES IN T1D

Physiological Responses to Moderate Physical Activity

Fuel metabolism. Several-fold increments in hormone concentrations contribute to the maintenance of fuel and fluid homeostasis during exercise (Meinders 1988, Koivisto 1992, Galassetti 2001, Kishore 2006, Diabetes Research in Children Network Study Group 2009). When individuals with T1D exercise with normal blood glucose levels, their substrate oxidation is similar to healthy individuals who experience a shift toward lipid oxidation during extended exercise. When exercising in a hyperglycemic state, however, fuel metabolism in T1D is dominated by carbohydrate oxidation, although muscular glycogen is not spared by the greater use of blood glucose (Jenni 2008). Exercise done with higher circulating insulin levels or during insulin peak times also increases blood glucose use (and the potential for hypoglycemia to develop) without sparing muscle glycogen (Chokkalingam 2007a). Some of the additional blood glucose uptake during high-insulin conditions actually may increase glucose flux through nonoxidative pathways (i.e., into glycogen storage). Regimen changes aimed at lowering insulin levels or increasing the availability of exogenous carbohydrates likely will be necessary to counteract the normal decline in blood glucose levels during such activities. During recovery from exercise, fat use dominates, particularly following long-duration exercise and during periods of worse glycemic control (Tuominen 1997b).

Hepatic glycogen. Liver glycogen is affected by glycemic control. In nondiabetic individuals, increases in hepatic glucose production during exercise are almost entirely the result of increased hepatic glycogenolysis; in contrast, in moderately controlled people with T1D, their increased rates of glucose production both at rest and during exercise are primarily accounted for by increased gluconeogenesis (Petersen 2004). In fact, poorly controlled individuals have a marked reduction in both hepatic glycogen synthesis and breakdown, which can be improved, but not normalized, by short-term restoration of normal levels of insulin and blood glucose (Bischof 2001). High levels of insulin and blood glucose during moderate exercise, however, do not suppress hepatic glycogen concentrations (Chokkalingam 2007b).

Specific Responses to High-Intensity Training

Moderate-intensity exercise has a greater potential to result in blood glucose reductions, but undertaking more vigorous activity actually may cause a deterioration in metabolic control not fully explained by hormonal responses of glucagon or catecholamines (Mitchell 1988). One study compared the blood glucose responses to intermittent high-intensity exercise and moderate-intensity exercise in individuals with T1D (Guelfi 2005a). The high-intensity protocol consisted of 30 min of continuous moderate exercise interspersed with 4-s sprints every 2 min to simulate the activity patterns of team sports, whereas the other involved the same length of moderate activity alone. Although both exercise protocols resulted in a decline in blood glucose, the glycemic decrement was greater with the moderate activity done by itself, despite the performance of a greater amount of total work with intermittent high-intensity protocol. For 1 h, blood glucose levels remained higher following the higher-intensity workout and were associated with elevated levels of lactate, catecholamines, and growth hormone during early recovery from exercise, with no differences in free insulin, glucagon, cortisol, or free fatty acids between the activities.

Thus, intermittent high-intensity exercise does not increase the risk of early postexercise hypoglycemia in individuals with T1D (Guelfi 2005b), which likely is related to a lesser decline in glycemia during exercise (due to greater hepatic glucose output) and attenuated blood glucose uptake during exercise and early recovery (Guelfi 2007). Such training also has been shown to enhanced muscle oxidative metabolism in young adults with T1D, which may have clinically important health benefits (Harmer 2008). It also may protect against nocturnal hypoglycemia in athletes with T1D (Iscoe 2011).

Case in Point: Continued

MF reveals that she used to be on many sports teams in high school: cross-country in fall, swimming in winter, and soccer in spring. She was not talented enough to get recruited to play any sports competitively in college, but she still enjoys many different types of activities. During further discussion, MF admits that she had trouble controlling her blood glucose levels in high school once she developed T1D and that she cut way back on her training because workouts often caused her blood glucose to go too low. In fact, her biggest fear related to starting an exercise training program again is the likelihood of more frequent hypoglycemia. She currently has hypoglycemia 1–2 times/week, and she is able to treat it as soon as symptoms develop, which for her is around a blood glucose level of 55–60 mg/dl. In high school, however, she had a couple of really bad overnight lows that required medical assistance to treat.

Additional Questions to Consider

1. What steps can MF take to prevent hypoglycemia both during and after exercise, given that her concerns about developing it are valid ones?

2. Can treating hypoglycemia have any impact on the possibility of MF reaching her stated body weight goals?

(Continued)

MAKING APPROPRIATE EXERCISE-RELATED REGIMEN CHANGES

A better understanding of the physiology of exercise with regard to fuel mobilization and other metabolic changes can suggest which problems may arise in managing diabetes during physical activity and sports participation. Any exercisers with diabetes need to be advised on appropriate diet and insulin management to maximize performance and reduce fatigue (Gallen 2011). With an appropriate adjustment of insulin dose and diet, people with T1D can even participate in competitive events and sports (Koivisto 1992). General management of blood glucose levels during and after exercise, hypoglycemia prevention and treatment, hyperglycemia and dehydration, and balancing insulin use with physical activity are all critical topics associated with exercise prescription for this group, and they are more fully discussed in chapters 11–14 of this book.

Self-Monitoring of Blood Glucose

Blood glucose responses to physical activity can vary with each exercise session, depending on its duration and intensity, and diabetes regimens (namely, insulin doses and food intake) will require adjustments to keep blood glucose levels balanced. Moderate aerobic exercise usually causes blood glucose levels to drop rapidly, while higher-intensity work may cause them to rise, thereby making glycemic control challenging. Accordingly, people who engage in any physical activity will need to use self-monitoring of blood glucose (SMBG) to better understand their glucose responses to a specific exercise bout and how to make appropriate regimen changes that effectively manage blood glucose levels, keeping in mind that both exercise adaptations and blood glucose responses are specific to the type of training.

Use of continuous monitoring. A more recent technology, continuous glucose monitoring (CGM), provides frequent interstitial glucose readings over a 24 h period and may be particularly helpful for individuals with T1D attempting to establish their usual glycemic responses, trends of hypoglycemia and hyperglycemia, and exercise effects (Riddell 2009, Maran 2010). Short-term use of CGM with alarms, together with appropriate instructions for users, reduces the incidence and duration of hypoglycemia, but only to a limited extent, in part because it tends to overestimate blood glucose levels in the low range and readings lag behind real-time values by 15–20 min (Davey 2010). Having the capacity to know their glucose levels and the direction of change during exercise increases self-efficacy in people who are prone to hypoglycemia and hyperglycemia (Riddell 2009).

Carbohydrate Intake

Sports and other carbohydrate drinks. Ingestion of carbohydrate-based drinks (or other sources of carbohydrate) is likely needed to prevent hypoglycemia both during and following physical activity in a T1D population, but the amount varies with the type of activity, exercise duration, and timing of activity relative to insulin dosing and doses. In one study, mean blood glucose levels were reportedly higher during 60 min of moderate treadmill walking in diabetic individuals consuming a glucose polymer sports drink group compared with placebo, and the same drink prevented the onset of postexercise hypoglycemia without causing or contributing to hyperglycemia (Tamis-Jortberg 1996). For 60 min of moderate cycling undertaken 3 h after breakfast (and the last dose of rapid-acting insulin), 40 g of a liquid glucose supplement, ingested 15 min prior exercise, is likely enough to maintain safe blood glucose levels in anyone on a basal-bolus regimen (e.g., Humulin N and lispro) without requiring changes in insulin doses (Dubé 2005). Ingestion of either whole milk or sports drinks designed for quick or long-lasting nutrient replenishment also has been used effectively to avoid late-onset, postexercise hypoglycemia (Hernandez 2000). For anyone using an insulin pump and engaging in moderate or vigorous activity without altering basal rates, ingestion of sugary drinks during exercise, reduction of the overnight basal rate, reduction of the predinner insulin bolus, or a bedtime snack should be considered to prevent hypoglycemia during and following exercise and overnight (Delvecchio 2009).

Daily carbohydrate intake. Endurance-training athletes usually are encouraged to take in a greater proportion of their total daily calories as carbohydrates, in addition to carbohydrate load before events (Burke 1999, American Dietetic Association 2009). This approach, however, may not be the best one for individuals with T1D. By way of example, an increased carbohydrate intake for 3 weeks in adult athletes with T1D was associated with deterioration in glycemic control, increased insulin requirements, decreased muscle glycogen content, and reduced exercise performance. Thus, consuming a high-carbohydrate diet when doing sport-specific training is not advisable, at least not when compensatory insulin changes are not made and the resulting glycemic control is worse (McKewen 1999). For most individuals, intake of at least 40% of calories from carbohydrates (without overdoing it), along with adequate protein and total daily calories, is more likely to result in optimal glycogen storage (American Dietetic Association 2009).

Insulin Adjustments

Making adjustments to insulin doses and timing of doses can lower the risk of hypoglycemia during and following exercise. For example, consumption of a low–glycemic-index carbohydrate (75 g of isomaltulose) and taking an insulin dose reduced by 75% just 30 min before undertaking 45 min of moderate running improves pre- and postexercise blood glucose responses in T1D (West 2011). Similarly, a 75% reduction of insulin with a meal taken 2 h before 45 min of moderate running results in the greatest preservation of blood glucose during and following exercise (compared with 0%, 25%, and 50% dose reductions) and allows for minimal intake of extra food to maintain euglycemia during the 24 h following the activity (West 2010).

Insulin regimen effects. The types of insulin and insulin regimens used can affect exercise-related adjustments. Insulin detemir is associated with less hypoglycemia than glargine in relatively well-controlled individuals with T1D both during and after exercise (Arutchelvam 2009). People treated with insulin detemir appear to improve their glycemic control with no increases in hypoglycemia, adverse events, or body weight (Marre 2009). Recently, it was reported that athletes with T1D who were treated with rapid-acting insulin analogs and participating in half-marathons required less insulin reductions compared to traditional guidelines, although they needed a significant quantity of carbohydrate supplements to avoid hypoglycemia during and after events (Murillo 2010). For children with T1D using an insulin pump, discontinuing basal insulin during exercise is an effective strategy for reducing hypoglycemia, but the risk of hyperglycemia is increased (Diabetes Research in Children Network Study Group 2006).

Insulin pump use. Other evidence is related to glycemic control in adolescents with T1D on insulin pump therapy doing moderate- or higher-intensity physical activity with their insulin pumps switched on or off (and compared with glargine use) (Delvecchio 2009). Postexercise blood glucose levels were significantly increased with the pump off and were unchanged or lower with the pump on and when compared with glargine. The authors concluded that in that case, it is advisable to leave the basal rate on during activity, but doing so may require consumption of carbohydrate during the exercise, a lower overnight basal rate, less of an insulin bolus for dinner, and a possible bedtime snack to prevent nighttime hypoglycemia.

Exercise timing. Finally, the time of day that exercise is done can also affect insulin requirements. One study compared cycling for 45 min moderately either 1 h after lunch with usual insulin doses or after an overnight fast without morning insulin (Biankin 2003). Reproducibility of the change in blood glucose levels during exercise after feeding in individuals on nonintensive insulin regimens was poor, but reproducibility was reasonable when fasting. Exercise does decrease the glycemic variability after a meal, meaning that blood glucose levels after exercise seek a reproducible “target.” Thus, the absolute glucose level after a typical bout of exercise in the fed state should be a good guide to carbohydrate or insulin adjustment on subsequent occasions.

Prevention of Hypoglycemia

Fear of hypoglycemia is the strongest barrier to regular physical activity in anyone with T1D, and information about and support for hypoglycemia management is critical (Brazeau 2008). Given the importance of this topic, it is more fully discussed in chapter 12. Various strategies and technologies have been developed to help detect and prevent hypoglycemia, including improved patient education, frequent SMBG, use of rapid-acting and basal insulin analogs, insulin pump therapy, exercise-related insulin modifications, and use of CGM (Realsen 2011).

Later-onset hypoglycemia. A major concern following exercise is the later, delayed onset of hypoglycemia, especially overnight during sleep. Overnight hypoglycemia after afternoon exercise has been shown to be common in children with T1D (Tsalikian 2005). A biphasic increase in glucose requirements to maintain euglycemia after exercise has been reported, suggesting a unique pattern of early and delayed risk for nocturnal hypoglycemia after afternoon exercise (McMahon 2007). Anyone with T1D should be made aware of this possibility to enable them to make adjustments in their management plans before and after any physical activity to minimize or avoid late-onset hypoglycemia (MacDonald 1987, Hernandez 2000, Kalergis 2003, Alemzadeh 2005, Tsalikian 2005, Diabetes Research in Children Network Study Group 2006, McMahon 2007, Tamborlane 2007, Cooperberg 2008, Wilson 2008).

Effects of sprints. A novel approach to hypoglycemia prevention during physical activity is related to the adrenergic effects of sprinting. After moderate-intensity exercise, young individuals with insulin-treated, complication-free T1D have engaged in a 10-s maximal sprint that acutely opposes a further fall in blood glucose compared with rest alone. The addition of the sprint after moderate-intensity exercise is a novel method to reduce the risk of hypoglycemia in active individuals (Bussau 2006). Along the same lines, a 10-s sprint performed immediately before moderate-intensity exercise also prevents blood glucose levels from falling during early recovery from moderate-intensity exercise in individuals with T1D (Bussau 2007). Doing intermittent, high-intensity training may result in a higher incidence of delayed nocturnal hypoglycemia (Maran 2010).

EXERCISE PRESCRIPTION FOR ADULTS AND YOUTH WITH T1D

Mode

Any form of aerobic exercise that utilizes large muscle groups and causes sustained increases in heart rate is likely to be beneficial to cardiovascular risk management (and possibly glycemic control) in children, adolescents, and adults with T1D (Orchard 2003, Costacou 2007, Bishop 2009, Shivu 2010, Maahs 2011). Undertaking a variety of modes of physical activity is recommended for all individuals to optimize training effects and lower injury risk (Physical Activity Guidelines Advisory Committee 2008). Examples of acceptable aerobic activities include both weight-bearing and non–weight-bearing ones, such as walking, jogging, running, cycling, swimming, water aerobics, aquatic activities, conditioning machines, dancing, chair exercises, rowing, and cross-country skiing, among others.

For children and adolescents ages 6 to 17 years, most of their physical activity should be either moderate- or vigorous-intensity aerobic activity, but it can include muscle-strengthening activities (even if unstructured and part of play, such as playing on playground equipment, climbing trees, and playing tug-of-war) and bone-strengthening activities like running, jumping rope, basketball, tennis, and hopscotch. Other more age-specific activities include skateboarding, rollerblading, martial arts, playing tag, wall rock climbing, gymnastics, soccer, and other competitive sports teams. Both adults and youth with T1D can safely and effectively participate in competitive athletic training and sports (Tuominen 1997a, 1997b; Cauza 2005; Graveling 2010; Murillo 2010).

Intensity

For adults, aerobic exercise should be moderate or vigorous intensity, corresponding to 40–89% of HRR (heart rate reserve; see chapter 4) (Garber 2011, Haskell 2007, Nelson 2007, Physical Activity Guidelines Advisory Committee 2008). Moderate-intensity exercise equates to 40–59% HRR, whereas vigorous-intensity exercise is 60–89% HRR (Garber 2011). A severely deconditioned person with T1D can start out at 30−39% HRR (“light”) and progress to more moderate levels.

For children and adolescents, recommended aerobic activities should be either moderate or vigorous intensity as well (40–89% HRR), but they also should include vigorous-intensity physical activity (60–89% HRR) at least 3 days a week (Physical Activity Guidelines Advisory Committee 2008).

A corresponding overall body rating of “somewhat hard” to “hard” is appropriate for most individuals with T1D (Garber 2011, Haskell 2007, Nelson 2007, Physical Activity Guidelines Advisory Committee 2008). Subjective intensity can be estimated using a scale of 0 to 10, where resting is 0, maximal effort is 10, moderate-intensity activity is 5 to 6, and vigorous-intensity activity is 7 to 8 on that scale (Physical Activity Guidelines Advisory Committee 2008).

Frequency

Adults with T1D should perform aerobic exercise at least 3–5 days/week, depending on exercise intensity and duration, but greater regularity may facilitate diabetes management in these individuals. Increased insulin sensitivity resulting from the last bout of exercise is relatively short lived, and more frequent participation in physical activity confers greater benefits in this regard (King 1995, Kirwan 2000, Clevenger 2002, Houmard 2004, Evans 2005, Hawley 2008, Bajpeyi 2009).

Children and adolescents should engage in daily physical activity, including aerobic, muscle-strengthening, and bone-strengthening activities (Physical Activity Guidelines Advisory Committee 2008). Not all three of these activities necessarily need to be done every day, although some overlap between categories exists.

Duration

Adults with T1D should engage in a minimum of 60–75 min/week of vigorous activity (>6 metabolic equivalents [METs]) or 150 min/week of moderate-intensity exercise (3–6 METs), performed for at least 20–30 min/session (minimum of 10-min bouts). As with all adults, around 150 min/week of moderate-intensity exercise is associated with reduced morbidity and mortality, but more health benefits may result from longer participation (Physical Activity Guidelines Advisory Committee 2008).

Children and adolescents should engage in 60 min (1 h) or more of physical activity daily, or minimally 420 min a week (Physical Activity Guidelines Advisory Committee 2008). This recommended duration, however, includes aerobic activities, usual play, and muscle- and bone-strengthening activities.

Progression

If an adult is already normally active or has a reasonable fitness level, he or she can skip the initial training phase and start directly with the improvement phase. Sedentary or deconditioned adults with T1D are advised to begin with low-intensity workouts (<40% HRR), gradually progressing in both exercise intensity and volume to minimize the risk of injury or noncompliance, particularly if he or she has any health complications (Physical Activity Guidelines Advisory Committee 2008). The initial focus should be on increasing frequency and duration of the exercise rather than intensity, although faster training intervals may be used to promote greater fitness and blood glucose management (Guelfi 2005a, 2005b; Guelfi 2007; Iscoe 2011). If weight loss is a major goal, then an exercise duration of ~7 h/week may be necessary (Pavlou 1989, Schoeller 1997, Weinsier 2002, Saris 2003, Donnelly 2009).

Youth should not solely do moderate-intensity activity, but rather they should include vigorous-intensity activities to elicit greater improvements in cardiorespiratory fitness; their activities, therefore, should progress to include ones of a higher intensity. If starting out deconditioned, they should slowly increase their activity in small steps and in ways that they enjoy. Once conditioned or if beginning at that level, they should maintain or increase their activity level beyond 60 min/day and vary the kinds of activities they do to reduce the risk of overtraining or injury. Adolescents and children with T1D may meet recommended levels of physical activity by doing free play, structured programs, or both (Physical Activity Guidelines Advisory Committee 2008). Structured exercise programs can include aerobic activities, such as playing a sport, and muscle-strengthening activities like lifting weights, using resistance bands, or using body weight for resistance (e.g., push-ups, pull-ups, and sit-ups). Muscle-strengthening activities count if they involve a moderate to high level of effort and work the major muscle groups of the body (i.e., legs, hips, back, abdomen, chest, shoulders, and arms). All of these recommendations are summarized for both adults and youth in Table 6.1.

Table 6.1 Recommended Aerobic Exercise Rx for Adults and Youth with Type 1 Diabetes

Mode	Adults: Walking, jogging/running, cycling, swimming, rowing, aquatic activities, team sports, dancing, conditioning machines, seated exercise, and more
Youth: Running, hopping, skipping, jumping rope, swimming, dancing, bicycling, basketball, tennis, skateboarding, rollerblading, and team sports
Intensity	Adults: 40–89% HRR (initial intensity may need to be lower for sedentary, deconditioned, and overweight individuals) Perceived exertion of “somewhat hard” (5–6 on 10-point scale) to “hard” (7–8)
Youth: moderate or vigorous intensity (40–89% HRR), but vigorous-intensity physical activity (60–89% HRR) at least 3 days a week Perceived exertion of “somewhat hard” (5–6) to “hard” (7–8)
Frequency	Adults: 3–7 days/week (including structured and lifestyle activity) 3 days of vigorous or 5 days of moderate intensity (greater regularity may facilitate diabetes management)
Youth: 7 days/week of physical activity (including aerobic, muscle-strengthening, and bone-strengthening activities)
Duration	Adults: At least 20–30 min/session (minimum 10-min bouts) Minimum of 150 min/week of moderate-intensity (3–6 METs) or 60–75 min/week of vigorous-intensity (>6 METs) physical activity
Youth: At least 60 min (1 h) of daily physical activity (420 min a week), including aerobic activities, usual play, and muscle- and bone-strengthening activities
Progression	Adults: Start out on the “low” side if deconditioned, and progress slowly over weeks to months; start with the “improvement” phase if fitness levels adequate Increase duration and frequency first, intensity last (with the possible exception of adding in faster intervals during exercise sessions)
Youth: Start out slowly with small increases in activity if deconditioned, but all should progress to engaging in vigorous activity at least three times weekly; once conditioned, maintain or increase activity level and vary activities to reduce the risk of overtraining or injury Possible to meet recommended levels of physical activity by doing free play, structured programs, or both

HRR, heart rate reserve; MET, metabolic equivalent.

Case in Point: Wrap-Up

Because MF desires to focus on both weight and diabetes management through her exercise program and her schedule is somewhat flexible in college, she decides to start regularly working out at her university’s student recreation center, where she has access to fitness equipment, classes, and other activities.

Exercise Program Goals

Mode of Activity: MF desires to undertake multiple training activities—she likes the idea of cross-training to get more fit and avoid injuries—so she can include conditioning machines (like cross-trainers and elliptical machines), lap swimming, and spinning (cycling) classes as some of her choices.

Intensity: Because MF is starting out somewhat deconditioned (except for walking around campus), she should start with more moderate activities (that feel “somewhat hard” or 5–6 on a 10-point scale) to start and work up to “hard” ones (7–8 using that scale). She should choose interval or hill workouts on the conditioning machines. Her initial target heart rate should start in a moderate-intensity range (130–152 bpm, or 40–59% HRR), with a target goal of 60–89% HRR (153–187 bpm), with a maximal target of 187 bpm (89% HRR). Her intensity during each training session can vary, however, and she may choose to do harder (vigorous) and easier (moderate) workout days to prevent overtraining.

Frequency: Depending on how MF alternates her training intensity, she should do 3–5 days of planned training a week (3 days if vigorous, 5 days if moderate, or a combination of the two intensities and frequencies), keeping in mind that being more regular with her training may make it easier for her to make regimen changes to manage her blood glucose levels. Her insulin action may stay higher following harder workout days, so she should plan to space out her more vigorous training days and intersperse more moderate ones in between them.

Duration: MF’s recommended duration is inversely related to her exercise intensity, meaning that working out harder requires a shorter duration. She should aim to do at least 20 min of vigorous physical activity or 30 min/session of moderate training, with a target training goal of 60–75 min of vigorous or 150 min of moderate exercise weekly, or a combination thereof. As a rule of thumb, 1 min of vigorous exercise is equivalent to 2 min of moderate activity.

Progression: Given her initial fitness status and prior sports history, MF can likely begin in the improvement phase of training. Initially, she may choose to only work out 3 nonconsecutive days/week, working up to 5 days/week, depending on her training intensity. Once she has established her aerobic training routine, she should consider adding in some resistance training at least 2 days/week to enhance her muscular strength as well. As she goes into the maintenance phase, she should continue to vary her activities or add in new ones for variety, additional fitness gains, injury prevention, and motivation to continue her training.

Daily Movement: Due to MF’s interest in losing weight, she should engage in more daily movement as well, including fidgeting, standing, and taking more steps during the day, to maximize her daily caloric expenditure. Doing so will help keep her blood glucose at a lower level.

Possible Precautions: Because MF has not had T1D for that long and has minimal risk factors for cardiovascular disease, she should not be required to have any testing done before starting an exercise program. MF should be advised to have her health-care provider prescribe a glucagon pen that she can keep in her dorm room as a treatment for severe hypoglycemia. She should instruct both her roommate and her dorm’s resident assistant how to give her a glucagon injection, should the need arise.

Regimen Changes: Because weight loss is a stated goal, MF will need to be especially vigilant about preventing hypoglycemia since the extra calories taken in during treatment of lows may sabotage her attempts to lose weight. Her insulin use does require planning ahead with appropriate insulin dosing and food intake changes to prevent hypoglycemia both during and following any physical activity. She will need to use SMBG frequently as she begins her training program—before, possibly during, and several times after exercising—to establish her usual responses to exercise and blood glucose trends. During exercise sessions, she should always have a rapid-acting carbohydrate like glucose tablets or gels readily available to treat low blood glucose with a minimal amount of calories. Once she starts exercising regularly, her basal insulin needs will likely decrease, and she may need to lower her bedtime dose of insulin glargine or eat a bedtime snack (but for weight-loss reasons, it would be better to minimize the need for additional snacking). Furthermore, for exercise sessions done within 1–2 h of a meal, she should consider decreasing her meal insulin (lispro) dose by up to 75% to prevent hypoglycemia during the activity, and she may need less insulin later in the day at subsequent meals.

Individuals of all ages with T1D can and should participate in regular physical activity for better health, although appropriate diabetes regimen changes must be made if improved blood glucose management is an expected outcome. Cardiorespiratory fitness levels may be lower in some individuals with T1D, and their metabolic responses to exercise can be altered by hyperglycemia. Prevention of hypoglycemia related to physical activity will likely require greater carbohydrate intake, reductions in insulin doses (or changes in timing), or both. Fear of hypoglycemia is the biggest barrier to exercise participation, but when diabetes is managed properly, youth and adults with T1D can participate in recommended amounts of physical activity following the same guidelines as their counterparts who do not have diabetes.

Professional Practice Pearls

• Regular exercise lowers blood pressure, lipid levels, body weight, mortality risk, and risk of complications while raising cardiorespiratory fitness levels, muscular strength, quality of life, and sense of well-being in individuals with T1D.

• Appropriate diabetes regimen changes must be made if improved blood glucose management is an expected outcome of regular physical activity.

• Some, but not all, individuals with T1D have the same aerobic capacity as similar-age people without diabetes.

• Moderate exercise usually causes a decline in blood glucose levels; conversely, high-intensity training can maintain more stable levels or possibly result in hyperglycemia.

• When engaging in regular physical activity, individuals with T1D will need to self-monitor their blood glucose levels to establish responses and make regimen changes.

• Regimen changes to manage glycemic balance with physical activity will likely involve greater food intake, changes in insulin doses and timing, or both.

• A novel approach to hypoglycemia prevention involves engaging in a 10-s maximal sprint immediately before or at the end of a bout of moderate activity.

• Adults with T1D should engage in at least 150 min a week of moderate exercise, 60–75 min of vigorous aerobic exercise, or a combination thereof on 3–5 days/week (depending on intensity).

• Deconditioned adults can start out with lower-intensity activities and progress slowly over weeks to months, or start with the improvement phase if fitness adequate.

• Youth with T1D should engage in at least 60 min or more of physical activity daily, 7 days/week, including aerobic, muscle-strengthening, and bone-strengthening activities.

• Children and adolescents should start out slowly if deconditioned, but all should progress to engaging in vigorous activity at least three times weekly.

• Youth should vary activities, but it is possible for them to meet the recommended levels of physical activity by doing free play, structured programs, or both.

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