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Chapter 1 Diabetes, Physical Activity, Exercise, and Fitness Overview

The burden associated with diabetes, prediabetes, and related metabolic disorders is undeniably growing. Federal government estimates released in 2011 placed the number of Americans with diabetes at nearly 26 million (with one-quarter of cases likely still undiagnosed)—or ~8.3% of the total population. Another 79 million American adults have prediabetes, which is an asymptomatic state characterized by moderate insulin resistance, impaired fasting glucose (IFG), or impaired glucose tolerance (IGT). People with prediabetes have glucose levels that are higher than normal but lower than those classified as diabetes. About 25% of individuals with prediabetes will develop type 2 diabetes (T2D) within 3 to 5 years (U.S. Department of Health and Human Services 2011). Moreover, it is now estimated that one in three Americans born in the year 2000 or later will develop diabetes during their lifetimes, with rates closer to 50% in high-risk, ethnic populations (Narayan 2003, 2006).

In spite of the salutary effects of achieving optimal blood glucose control, only slightly more than half of individuals with diabetes currently are reaching recognized treatment goals (Cheung 2009). Although physical activity has long been considered a cornerstone of diabetes management and a critical factor in optimizing treatment, prescribing specific exercise for individuals with various types of diabetes (or even prediabetes) can be a daunting task for the time-pressured health-care provider or the diabetes-naïve fitness professional. A fundamental need in facilitating such exercise prescription is an enhanced understanding of the types of diabetes and how physical activity requirements and abilities may differ among them.

Case in Point: Weight, Blood Pressure, and T2D

MJ, a 48-year-old woman diagnosed with T2D 4 years ago, is having trouble controlling her weight and blood pressure. She wants to discuss safe and appropriate ways to be more physically active to address these issues and improve her overall health and diabetes management. From her physician, she already has received medical clearance to start increasing her activity level with no specific restrictions. Her medications include a sulfonylurea (glipizide) and an antihypertensive agent. MJ reports testing her blood glucose usually just once a day in the morning before breakfast. She currently is not doing any planned exercise and has not been active for the past 10 years or so, although she claims to be motivated to start being more physically active now to increase her energy levels.

Resting Measurements

Height: 64 inches

Weight: 190 lb

BMI: 32.6 kg/m² (obese)

Heart rate: 85 beats per minute (bpm)

Blood pressure: 138/86 mmHg (on medication)

Fasting Labs

Plasma glucose: 148 mg/dl A1C: 7.4%

Total cholesterol: 190 mg/dl

Triglycerides: 200 mg/dl

High-density lipoprotein cholesterol: 38 mg/dl

Low-density lipoprotein cholesterol: 112 mg/dl

Questions to Consider

1. How should MJ go about increasing her physical activity level?

2. Does MJ need to take any precautions related to exercise participation?

3. What strategies will help motivate MJ and support her efforts to establish regular physical activity as a lifelong habit?

(Continued)

BASICS OF DIABETES SELF-MANAGEMENT

Effective management of any type of diabetes involves use of self-monitoring of blood glucose (SMBG), administration of appropriate medications to regulate blood glucose levels, regular participation in physical activity and exercise, and body weight management, as well as dietary and other lifestyle improvements, for example, stress management (St John 2010, American Diabetes Association 2013b). Regular physical activity facilitates improved blood glucose control in T2D and may offer a similar benefit in gestational diabetes mellitus (GDM) (Dyck 1998, Davenport 2008, Colberg 2010). Although regular exercise does not uniformly improve glycemic management in those with type 1 diabetes (T1D) unless appropriate regimen changes are made, exercise is still considered a safe and effective adjunct therapy for diabetes management and complication prevention (American Diabetes Association 2013b). Exercise interventions for individuals with diabetes ideally should involve a multidisciplinary team of specialists that includes the diabetes (or other qualified) physician, certified diabetes educator, registered dietician, and exercise professional to facilitate individual education and lifestyle changes to manage this disease. Self-management skills are essential to success, and diabetes education is an important tool to improve glycemic control, regardless of the type of diabetes that an individual has (American Diabetes Association 2013b).

CLASSIFICATION AND ETIOLOGY OF DIABETES

Four classifications of diabetes are categorized based on etiology: T1D, T2D, GDM (diagnosed during pregnancy), and diabetes resulting from other specific origins (e.g., genetic defects, drugs and chemicals, pancreatic disease, surgery, and infections). The major types are T1D and T2D, with the latter type describing 90–95% of all cases, whereas T1D accounts for only 5–10% of the population with diabetes (American Diabetes Association 2013a). The major characteristics of these classifications are given in Table 1.1.

Table 1.1 Characteristics of T1D, T2D, and Gestational Diabetes

T1D

T1D is caused by autoimmune destruction of pancreatic β-cells usually leading to an absolute deficiency of insulin secretion and likely triggered by environmental factors that remain poorly defined or predicted (American Diabetes Association 2013a). Formerly called juvenile-onset or insulin-dependent diabetes, T1D is commonly diagnosed in children and adolescents, but this immune-mediated type of diabetes can occur in individuals of any age. About half of the cases of T1D currently are being diagnosed in adults and frequently are diagnosed and classified as latent autoimmune diabetes of the adult (LADA). Rates of β-cell destruction involved in the onset of T1D generally are slower in older-onset cases than in youth—thus giving rise to the LADA category, which is still not clearly defined or universally used. In addition, many older individuals with this type of diabetes initially may be misdiagnosed with T2D instead.

T2D

Insulin resistance is the hallmark of T2D, and the risk of developing it increases with age, obesity, and physical inactivity. Genetic and environmental factors are strongly implicated in the development of T2D, but they are complex and not clearly defined. Some β-cell dysfunction or β-cell loss is evident at onset, leading to relative rather than absolute defects in insulin secretion (American Diabetes Association 2013a). This type of diabetes disproportionately affects ethnic minorities: its prevalence rates are about twofold greater in Hispanic and Latino, African American, Native American, Asian, and Pacific Islander populations than in non-Hispanic whites (U.S. Department of Health and Human Services 2011). It is also more common in individuals with hypertension or dyslipidemias and in women with a prior history of GDM (American Diabetes Association 2013a). Formerly called adult-onset or non–insulin-dependent diabetes and associated with older age, this type of diabetes leads many individuals to become insulin-requiring over the course of the disease. Moreover, its diagnosis in youth has risen dramatically over the past two decades. The initial diagnosis of T1D in children and adolescents can be complicated by the presence of insulin resistance and obesity, although recognition of T2D in youth may be delayed by the misconception that only adults can develop it.

Gestational Diabetes

GDM is also on the rise and is associated with a 40–60% chance of the mother developing T2D in the next 5 to 10 years (U.S. Department of Health and Human Services 2011, American Diabetes Association 2013a). Moreover, it is known to be potentially harmful to both mother and fetus if not controlled (Hapo Study Cooperative Research Group 2008, Metzger 2010). For example, larger or fatter infants have been shown to be more likely to develop both hypoglycemia and hyperinsulinemia in the few hours following birth, suggesting a strong relationship between maternal glycemia and fetal insulin production (Metzger 2010). It is generally diagnosed with a 75 g oral glucose tolerance test (OGTT) that is given to all women not known to have prior diabetes at 24–28 weeks of gestation. Given the rise in prevalence of undiagnosed T2D among women of childbearing age, however, it is now reasonable to screen women with diabetes risk factors at their initial prenatal visit. Women with GDM also should be screened for persistent diabetes 6–12 weeks postpartum (American Diabetes Association 2013a, 2013b).

DIAGNOSIS OF DIABETES

T1D and T2D

Currently, the American Diabetes Association recommends the use of any of the following four criteria for diagnosing diabetes: 1) hemoglobin A1C value of 6.5% or higher; 2) fasting plasma glucose ≥126 mg/dl (7.0 mmol/l); 3) 2 h plasma glucose ≥200 mg/dl (11.1 mmol/l) during an OGTT using 75 g of glucose; or 4) classic symptoms of hyperglycemia (e.g., polyuria, polydipsia, and unexplained weight loss) or hyperglycemic crisis with a random plasma glucose of 200 mg/dl (11.1 mmol/l) or more (American Diabetes Association 2013a, 2013b) (Table 1.2). In the absence of unequivocal hyperglycemia, the first three criteria should be confirmed by repeat testing on a second occasion.

Table 1.2 Diagnosis of Diabetes by Type

Gestational Diabetes

The International Association of Diabetes and Pregnancy Study Groups recently developed revised recommendations for the diagnosis of GDM (International Association of Diabetes 2010). After an overnight fast of at least 8 h, the pregnant woman ingests 75 g of glucose orally, with monitoring of fasting plasma glucose and 1 and 2 h postingestion glucose values. The diagnosis is made when any one of the following plasma glucose values is exceeded: fasting ≥92 mg/dl (5.1 mmol/l); 1 h ≥180 mg/dl (10.0 mmol/l); or 2 h ≥153 mg/dl (8.5 mmol/l) (American Diabetes Association 2013a, 2013b). It is expected that these new criteria will increase the prevalence of GDM because they require only that one abnormal value be recorded, whereas the former criteria required two to be met. Also, given that some cases diagnosed during pregnancy are actually cases of undiagnosed T2D, it is recommended that women with a history of GDM be screened for diabetes 6–12 weeks after delivery, using nonpregnant diagnostic criteria during an OGTT (American Diabetes Association 2013a).

Prediabetes

Individuals with prediabetes have glucose levels that do not meet the criteria for diabetes, but that are higher than normal, putting them at risk for related metabolic disorders. They can meet one or both criteria for IFG and IGT to be classified as being at high risk for developing T2D, or their overall glucose levels can exceed normal (as determined with an A1C test). Currently, prediabetes is diagnosed with fasting plasma glucose of 100–125 mg/dl (6.1–6.9 mmol/l) (i.e., IFG), 2 h OGTT plasma glucose of 140–199 mg/dl (7.8–11.0 mmol/l) (i.e., IGT), or an A1C of 5.7%–6.4%.

PHYSICAL ACTIVITY VERSUS EXERCISE

Before the discussion moves from what type of diabetes an individual has to which type of activity he or she should be doing, the professional needs to understand the meaning of the terms physical activity and exercise, which are used interchangeably in this book. By definition, physical activity is any bodily movement produced by the contraction of skeletal muscle that substantially increases energy expenditure (above resting), whereas exercise training is the subset of planned, structured, and repetitive bodily movements done with the intention of developing or maintaining physical fitness, which includes cardiovascular, strength, and flexibility training options (Haskell 2007, Nelson 2007).

Although use of the broader “physical activity” in place of the narrower “exercise” has caused some confusion even among health-care and fitness professionals, the intent is simply to recognize that many types of movements can have a positive impact on health-related physical fitness without qualifying as a planned exercise. In fact, more than one type of physical activity (such as combined aerobic and resistance training programs, along with lifestyle movement) is frequently required to yield measurable improvements for each of the components in the health-related fitness category.

Exercise training programs for individuals with diabetes typically include activities to enhance cardiovascular capacity (aerobic fitness) and muscular fitness and strength in people of all ages, as well as flexibility and balance in older individuals. Each person’s exercise program, however, should be modified according to his or her habitual physical activity, physical function, health status, exercise responses, and stated goals (Garber 2011). Adults who are unable or unwilling to meet the recommended minimal exercise targets can still benefit from engaging in amounts of exercise and other physical activities (like daily movement) that fail to meet those levels. Such strategies can be used when helping individuals with and at risk for diabetes make positive and lasting changes in their physical activity and exercise habits.

UNDERSTANDING AND DEFINING PHYSICAL FITNESS

It is imperative that health-care and fitness professionals use the same fitness terminology. Physical fitness has long been defined as “a set of attributes that people have or achieve relating to their ability to perform physical activity” (Caspersen 1985). What complicates physical fitness is that there are many different reasons to engage in a physically active lifestyle, including gaining positive health outcomes and optimizing sports and athletic performance. To simplify matters, the following table (Table 1.3) organizes the accepted terminology into four different categories of physical fitness: physiological fitness, health-related fitness, skill-related fitness, and sports.

The terminology of fitness is intended to be inclusive rather than athletic in nature when considering what affects an individual’s fitness level and health outcomes. For instance, individuals with diabetes do not need to have skill-related talents, participate in sports, or work out at a fitness club to achieve physiological or health-related benefits from increased physical fitness. Thus, a primary goal of the diabetes health-care and fitness professionals should be to encourage individuals to engage in appropriate physical activities to help them achieve positive health- and fitness-related outcomes.

Table 1.3 Fitness Categories and Related Terminology

Category	Related Terminology
Physiological	Metabolic Morphological Bone integrity Other
Health related	Cardiovascular fitness Musculoskeletal fitness (endurance and strength) Flexibility Body composition
Skill related	Agility Balance Coordination Power Speed Reaction time Other
Sports	Team Individual Lifetime Other

Physiological Fitness

Physiological fitness in particular relates to how an individual performs a physical activity, given that physiological fitness is most influenced by the regular inclusion of habitual physical activity (or, conversely, physical inactivity). In particular, metabolic fitness refers to the status of metabolic systems and variables predictive of the risk for diabetes and cardiovascular disease; increases in fitness lower the risk of both diabetes and heart problems (Simmons 2008, Sui 2008, Look Ahead Research Group 2010, Seeger 2011). Similarly, morphological fitness focuses on improvement in body compositional factors, such as body circumference, body fat, and regional body fat distribution, all of which can affect metabolic health and diabetes management (Jacob 2006, Iqbal 2007, Wang 2008, Lee 2009). Finally, bone integrity refers to bone strength and the status of bone mineral density, which can be positively affected by regular participation in almost any type of physical activity (Gorman 2012).

Health-Related Physical Fitness

Although it is closely related to the aforementioned category of physiological fitness with regard to metabolic health, the health-related physical fitness category contains terms that are recognized for their direct relationship to good health: cardiovascular fitness, musculoskeletal fitness, body composition, and flexibility. All of these components of fitness are important for patients with diabetes for optimal health and performance. For the individual engaging in a fitness program, many of these components are measurable over time, such as changes in body composition with exercise training or body fatness during weight loss or regain. Success of interventions often is judged on the basis of such changes.

A frequently measured parameter associated with exercise training is cardiovascular fitness (also known as cardiorespiratory fitness or aerobic fitness), which is the ability of the circulatory and respiratory systems to supply oxygen during sustained physical activity (McGavock 2004, Church 2005, Sui 2008, Lee 2009, Williams 2011). Musculoskeletal fitness includes both muscular endurance and muscular strength, which reflect the ability to continue to perform without fatigue and maximal ability to exert force, respectively (American College of Sports Medicine 2009). Flexibility measures the range of motion available at a joint (Herriott 2004). Finally, body composition in this health-related category refers to the relative amounts of fat and fat-free mass that an individual has (which can affect overall health); the fat-free component includes muscle, bone, body water, organs, and other body parts that are not fat (Lee 2005, Iqbal 2007, Wang 2008, Chomentowski 2009, Bray 2012, de Souza 2012). Excess body fat can affect both physiological and health-related fitness, depending on its relative amount and regional distribution.

Case in Point: Continued

A thorough interview with MJ to discuss her personal beliefs, past experiences, preferences, and concerns about increasing her activity levels is required to assist the health-care or fitness professional working with her to gain a better understanding of MJ’s view of physical activity. Any preprogram conversations also should include a discussion of the possibility of developing hypoglycemia during or after physical activity (given her use of a sulfonylurea), the best types of carbohydrates to keep handy during all activities (like glucose tablets or gels or hard candy), and the importance of monitoring blood glucose before and after exercise to establish typical response patterns. Once her exercise routine is established, she may need to talk with her health-care provider about possibly reducing her medication dose to prevent hypoglycemia.

(Continued)

HEALTH EFFECTS OF PHYSICAL ACTIVITY AND FITNESS FOR DIABETES

Although many American adults are not physically active, just 39% of adults with diabetes in the U.S. are physically active—defined as engaging in moderate or vigorous activity for at least 30 min thrice weekly—compared with 58% of other adults (Kirk 2004, Morrato 2007). In spite of the fact that myriad studies have shown that physical activity has a positive impact on diabetes management and prevention of complications, many health-care providers still are hesitant to prescribe it, and fitness professionals may be ignorant of precautions needed to handle the complexities of the disease with exercise as an added variable. Moreover, giving diabetic individuals a full exercise prescription that takes comorbid conditions into account may be too time-consuming for or beyond the expertise of many health-care and fitness professionals.

Unfortunately, simply instructing diabetic individuals to “exercise more” is frequently not motivating or sufficiently informative to get them regularly and safely active enough to benefit their fitness levels, diabetes control, and overall health (Morrato 2006). Moreover, professional books with exercise information and prescriptions have not been up to date or interactive enough to provide busy professionals with access to the latest tools and recommendations for each individual’s unique circumstances and requirements, and exercise remains woefully underprescribed for individuals with diabetes, almost all of whom can benefit from it immensely.

Prevention of T2D with Physical Activity

The “exercise is medicine” dogma launched by the American College of Sports Medicine campaign in 2007 cites diabetes as one of its hallmark diseases. At this point, it has been well established that participation in regular physical activity as part of lifestyle improvements can prevent or delay the onset of T2D (Tuomilehto 2001, Knowler 2002, Duncan 2003, Laaksonen 2005, Hamman 2006, Li 2008). Early on, studies assessing physical activity via self-report showed that higher levels are associated with reduced risk for T2D, regardless of the method of physical activity assessment or types of activities (Helmrich 1991, Manson 1991, Hu 1999). Greater volumes of physical activity may provide more protection, although both moderate walking and vigorous activity are associated with a decreased risk, as is better cardiovascular fitness (Wei 1999, Sui 2008).

In three larger intervention studies, the role of physical activity in T2D prevention in high-risk individuals has been examined (Diabetes Prevention Program [DPP] Research Group 2002, Knowler 2002, Pan 1997). Amazingly, all their results were similar, showing that modest weight loss (~7% reduction in initial body weight) combined with increased physical activity and dietary improvements (a healthier low-calorie, low-fat diet) significantly reduces the incidence of developing T2D and that these lifestyle changes were more effective in older individuals. The first of these studies, the Chinese Da Qing study, included an exercise-only treatment arm that showed that even modest changes in exercise (i.e., 20 min of mild or moderate, 10 min of strenuous, or 5 min of very strenuous exercise 1–2 times a day) can reduce diabetes risk by 46% compared with 42% for diet plus exercise and 31% for diet alone (Pan 1997). Both the Finnish Diabetes Prevention Study (Eriksson 1999, Tuomilehto 2001) and the DPP (Knowler 2002) included intensive, lifestyle modifications targeting modest weight loss, dietary improvements, and an average of 30 min of daily, moderate physical activity (Eriksson 1999, Tuomilehto 2001). The DPP, which studied 3,234 high-risk men and women, consisted of medication (metformin), lifestyle modification, and control groups (Knowler 2002). In the DPP, intensive lifestyle modification resulted in a 58% risk reduction that was almost twice the impact of metformin use (31% reduction). Although weight loss was the dominant predictor of a lower incidence of diabetes, the DPP showed that regular participation in physical activity can reduce risk by 44% even when modest weight-loss goals are not achieved (Laaksonen 2005, Hamman 2006, Lindstrom 2006). In summary, physical activity does play a role in preventing T2D in high-risk individuals, across ethnic groups, and in both sexes (Kosaka 2005, Ramachandran 2006).

Moderate exercise like brisk walking reduces risk of T2D (Helmrich 1991, Hu 1999, Hu 2001, Kosaka 2005, Ramachandran 2006). A meta-analysis that assessed the preventive effects of moderate-intensity physical activity reported that walking on a regular basis, typically done for 2.5 h per week or more, significantly reduces diabetes risk (Jeon 2007). The preventive effects of resistance training have not been studied to date. Likewise, although T2D is increasing in prevalence in children and adolescents, no trials have been completed that address whether physical activity or exercise prevents T2D in youth.

Limited studies suggest that to prevent and manage T2D, goals for youth should include limiting daily screen time (television, computer, or video game) to <60 min per day and doing at least 60 min of daily physical activity (McGavock 2007). The Treatment Options for Type 2 Diabetes in Adolescents and Youth (TODAY) study (Zeitler 2012) assessed the importance of physical activity as part of a behavioral lifestyle intervention to prevent T2D in youth. The results suggested that metformin combined with lifestyle intervention (e.g., greater physical activity) was intermediate in their ability to manage blood glucose levels and not significantly different from the use of medications (either metformin alone or metformin plus rosiglitazone).

Acute Effects of Physical Activity on Insulin Action and Hormones

Insulin. Most benefits of physical activity on diabetes management and prevention of T2D are likely due to acute and chronic improvements in insulin action (Boulé 2001, O’Gorman 2006, Galbo 2007). The acute effects of a recent bout of exercise account for the majority of these improvements, but are short-lived, whereas regular exercise training generally results in a more lasting effect. Although responses can vary, most people with any type of diabetes experience a decrease in their blood glucose levels during mild- and moderate-intensity exercise and up to 2–72 h afterward, necessitating frequent participation to maintain enhanced insulin action (Cartee 1989, Boulé 2001, O’Gorman 2006, Galbo 2007).

Although exercise cannot prevent T1D, it can lessen the potential decrements in insulin action that can occur due to inactivity; even individuals with T1D can become similarly insulin resistant and require larger insulin doses to manage blood glucose levels when not engaging in regular physical activity (Okamoto 2011). Circulating insulin levels during exercise must usually be lowered with appropriate dosing and timing of doses of exogenous insulin, however, to replicate the most normal physiological responses possible to prevent hypoglycemia, along with ingestion of additional carbohydrates to maintain blood glucose levels during most exercise sessions (Chokkalingam 2007a, Gallen 2011, West 2011).

Glycogen stores in the liver and skeletal muscles need to be replenished following each bout of physical activity, which is accomplished via an increased rate of blood glucose uptake during recovery from exercise until the depleted glycogen stores are fully replaced. This activity may take 24 to 48 h to complete, during which time both insulin sensitivity and fat oxidation in skeletal muscles usually are enhanced (Cartee 1989, Goodpaster 2003, Boon 2007). Combined hyperinsulinemia and hyperglycemia during moderate exercise in individuals with T1D, however, does not suppress the release of hepatic glycogen to maintain blood glucose levels (Chokkalingam 2007b), although total body glucose uptake is increased by having higher insulin levels (Chokkalingam 2007a).

Glucose-raising hormones. Endogenous insulin secretion normally decreases during exercise in people without diabetes and in most people with T2D who still secrete insulin. Its suppression is an essential step in allowing hepatic glucose production to ramp up to maintain the balance of glucose in the blood (Galbo 2007, Szewieczek 2009). Exercise causes the release of glucose-raising hormones like epinephrine and norepinephrine in an intensity-dependent manner, with exponentially more being released in response to intense compared with moderate- or low-intensity activity (Manetta 2002, Kreisman 2003). Other hormones like glucagon, cortisol, and growth hormone significantly influence how the primary fuel substrates (i.e., carbohydrate, protein, and fat) are mobilized and used for energy production (Kreisman 2003). Exercise-induced changes to the secretion of key hormones, as shown in Table 1.4, allow alternate fuels to be made available as energy sources while maintaining glucose homeostasis. In individuals dependent on exogenous insulin, these counterregulatory hormone responses can be altered. For example, growth hormone secretion during exercise in T1D has been found to be normal as long as normal blood glucose levels are maintained, but it is suppressed during hyperglycemic conditions (Jenni 2011).

Table 1.4 Metabolic and Exercise Responses of Hormones

Health Benefits of Chronic Exercise Training

The benefits of regular physical activity participation are numerous. Current evidence suggests physical activity improves insulin action, lowers blood glucose levels, improves BMI (commonly placing individuals into categories of normal, overweight, or obese based on weight and stature), and reduces multiple risk factors for cardiovascular disease (Kang 1996, Cuff 2003, Goodpaster 2003, Kriska 2006, Zoppini 2006, Hordern 2008). These important metabolic changes demonstrate the significant role that physical activity and exercise have in the prevention and management of T2D, in particular. Blood glucose management with physical activity as an added variable in T1D can be more challenging, but most of the same metabolic and overall health benefits are possible for these individuals as well (as shown in Table 1.5).

Table 1.5 Health Benefits of Regular Physical Activity Participation

Many research studies have found lower levels of cardiovascular fitness in individuals with prediabetes and T2D, in particular (Church 2005, Simmons 2008, Sui 2008, Lee 2009), but even in some children and adults with T1D (Williams 2011). Fitness gains are certainly possible for individuals undergoing training, but professionals should take this finding into account when prescribing appropriate exercise training regimens for anyone with diabetes. On the other hand, not everyone with diabetes has a lower fitness level to start. For example, a recent study examined whether glycemic status influences aerobic function in women with T1D and whether aerobic function is reduced relative to healthy women (Item 2011). There were no differences, however, between the two groups, either in the oxidative enzyme activity or in capillary-to-fiber ratio. Their mitochondrial capacity depended on the A1C level in untrained women with T1D, but it was not reduced relative to untrained healthy women. Exercise training in children with T1D has been shown to effectively reverse endothelial dysfunction and improve physical fitness, demonstrating that engaging in appropriate training is important for all individuals with any type of diabetes (Trigona 2010, Seeger 2011).

Case in Point: Wrap-Up

In MJ’s case, because she has been sedentary and is obese, it is best to start with exercise done at a lower intensity and progress her slowly with structured activities to avoid the development of athletic injuries, exercise nonadherence, or lack of motivation, with a goal of increasing her amount of physical activity gradually over a period of weeks to months.

Exercise Program Goals

Activity: The initial focus will be on lifestyle physical activity that MJ enjoys doing and can easily fit into her lifestyle, such as daily walking.

Intensity, Frequency, and Duration: Because MJ is currently inactive, she should be encouraged to start with short activity bouts of low- to moderate-intensity forms of physical activity that can be incorporated into her daily routine, such as doing 5–10 min of slow walking several times daily, 5–6 days a week. The exercise duration then can be increased gradually to 10 min per session, three times a day, and the walking speed increased slowly. Short intervals interspersed into her normal walking will improve her fitness levels more quickly and assist in management of blood glucose levels and postactivity blood pressure as well.

Progression: Long-term exercise goals should focus on progressively increasing amounts and frequency of activity to reach the minimum recommended levels of 150 min of moderate or vigorous exercise spread throughout the week, and MJ should be advised to add in some resistance training at least 2 days a week as well.

Daily Movement: For weight management purposes, MJ’s goal is to maximize her caloric expenditure each week with planned activities, but also by adding in greater daily movement during nonexercise times (i.e., more daily living activity). The professional working with her can help her to identify physical activities that she might be interested in trying to incorporate into her daily lifestyle, even if it is simply to stand more each day or take more daily steps (which can easily be measured by wearing a pedometer).

Behavioral Changes: MJ’s self-efficacy in being active can be enhanced by helping her to set realistic and specific goals that she can successfully accomplish, such as making a list of five ways to be more active throughout the day and trying one of them each week. She should be encouraged to ask questions and come up with her own ideas and suggestions for overcoming her exercise barriers and becoming (and staying) more physically active.

For most people with any type of diabetes, exercise can be undertaken safely and blood glucose levels can be managed effectively to the overall benefit of their diabetes management and health. Professionals who interact with people with any type of diabetes have an important and challenging role in helping them become and stay more physically active to manage their diabetes and their health.

Professional Practice Pearls

• Although diabetes is categorized into four main types, most individuals have T2D (90–95% of cases), are overweight or obese, and have a sedentary lifestyle.

• T1D can occur at any age; when its onset is during adulthood, it can be classified as LADA and may (at least initially) be misdiagnosed as T2D.

• Although exercise is technically a planned activity that is a subset of the broader term physical activity, they both involve bodily movement and can be used interchangeably.

• The terminology of fitness is intended to be inclusive rather than athletic in nature when considering what affects an individual’s fitness level and health outcomes.

• The potential health benefits of regular physical activity participation are numerous and include lowering the risk for development of T2D.

• Individuals with diabetes, particularly those with T2D, may be starting their exercise programs with cardiovascular fitness levels that are lower than normal for their age.

• Enhanced insulin sensitivity, which follows an acute bout of exercise, can lower insulin needs for a period of hours to days afterward and may increase the risk of hypoglycemia.

• Physical activity improves insulin action, lowers blood glucose levels, improves BMI, and reduces multiple risk factors for cardiovascular disease in diabetes.

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