Special Considerations for Type 1 and Type 2 Diabetes Mellitus
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Diabetes mellitus is characterized by abnormal glucose metabolism resulting from defects in insulin release, action, or both (5). According to the Centers for Disease Control and Prevention (CDC) (17), 29 million people or 9.3% of the U.S. population have diabetes, with 28% of those undiagnosed. This complex metabolic disease requires rigorous self-management combined with an appropriate balance of nutritional intake, medication(s), and regular exercise for blood glucose control. This chapter focuses on the most common forms of diabetes: Type 1 diabetes (T1D) and Type 2 diabetes (T2D). Safe and effective exercise recommendations are presented to assist in diabetes management and the associated diabetes-related health complications.
Mrs. Case Study-DM
Mrs. Case Study-DM, a 52-year-old woman diagnosed with T2D 7 years earlier, was having trouble controlling her weight and blood pressure (BP). She is 1.63 m (64 in) tall and weighs 86 kg (190 lb), classifying her as obese based on a body mass index of 33 kg ∙ m−2. Her resting heart rate is 85 bpm, and her resting BP is 138/86 mm Hg (medicated). Her lab work showed her to be in suboptimal control of her diabetes, with a fasting plasma glucose of 158 mg ∙ dL−1 and a glycolated hemoglobin (HbA1C) of 7.2% (indicating an average blood glucose level of around 160 mg ∙ dL−1 over the prior 2–3 months). Her lipid profile revealed a total cholesterol of 190 mg ∙ dL−1, high-density lipoprotein cholesterol (HDL-C) at 38 mg ∙ dL−1 with elevated low-density lipoprotein cholesterol (LDL-C) and fasting triglycerides (132 mg ∙ dL−1 and 200 mg ∙ dL−1, respectively). She reported testing her blood glucose fairly regularly (i.e., at least once a day).
Her medications included DiaBeta (sulfonylurea) and an antihypertensive agent. She was not currently participating in any structured exercise and had not regularly participated in the past. She stated that she was motivated to be more active mainly because of her physician’s recommendation and her unhappiness with her weight gain. She received medical clearance from her doctor to start increasing her activity level with no specific restrictions. Her physician referred her to a certified fitness professional to discuss safe and appropriate ways to be more physically active and improve her overall health and blood glucose management.
The fitness professional working with Mrs. Case Study-DM interviewed her to discuss her personal beliefs, past experiences, preferences, and concerns regarding exercise. The fitness professional reminded Mrs. Case Study-DM of the importance of monitoring her blood glucose before and after exercise and carrying a form of carbohydrate during activity. She was also told that in her case, it would be best to start with exercise at a low intensity and progress slowly with structured activities to avoid the development of activity-related injuries, exercise nonadherence, or lack of motivation, with a goal of increasing her amount of exercise gradually over a period of weeks to months.
The initial focus of her exercise program was on lifestyle exercise using low- to moderate-intensity types of exercise, particularly focusing on ones that she enjoys doing. Because Mrs. Case Study-DM was sedentary, the fitness professional encouraged inclusion of short activity bouts that could be incorporated into her daily routine. She was advised to start with a walking program consisting of 5–10 minutes of slow walking several times each day, 5–6 days a week. The exercise duration was to be gradually increased to 10 minutes per session, 3 times a day, and walking speed increased slowly as tolerated. Mrs. Case Study-DM was encouraged to engage in more daily movement and to use strategies to break up her sedentary time whenever possible. Her long-term exercise goals focused on progressively increasing amounts and frequency of activity to minimum recommended levels (150 min of moderate-to-vigorous exercise spread throughout the week, with no more than 24 h of inactivity between exercise sessions) (3).
In addition to helping Mrs. Case Study-DM identify activities that she might be interested in trying to incorporate into her daily lifestyle, the fitness professional suggested that she try using a simple pedometer (step counter) to obtain feedback about her activity levels, with a goal of increasing her number of baseline steps over a period of weeks to months. Behavior change strategies appropriate for the contemplation and preparation stages were used, including offering information on the benefits of exercise, discussing the pros and cons of increasing exercise, helping Mrs. Case Study-DM identify and build a support system, and identifying barriers to exercise and brainstorming possible solutions. Self-efficacy was enhanced by helping her set goals that were likely to be reached, such as making a list of five ways to be more active throughout the day. Finally, Mrs. Case Study-DM was encouraged to ask questions and come up with ideas for becoming more active to promote autonomy and build confidence to promote adherence to her new fitness-promoting lifestyle choices.
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T2D accounts for 90% of all diabetes, with T1D making up the remaining 5%–10% (5). Although T1D is one of the most common chronic diseases diagnosed in children, it also occurs in adults, usually with a slower onset than typically seen in youth (5). Likewise, although T2D was formerly seen mostly among older adults, the diagnosis in youth has risen dramatically over the past two decades (9). The burden of diabetes disproportionately affects minorities. It is now estimated that 1 in 3 Americans born in 2000 or later will develop diabetes during their lifetimes, with rates closer to 50% in high-risk, ethnic populations (57,58).
Diabetes-related complications exacerbate morbidity and increase the likelihood of physical limitation or disability (34). Hyperglycemia for an extended period of time is linked with chronic diabetes-related complications that worsen macrovascular, microvascular, and neural processes. Because of daily fluctuations in blood glucose occurring in diabetes, therapeutic interventions focus on blood glucose control, management of heart disease risk factors, and prevention of diabetes-related complications (30,32).
The diagnosis of diabetes is based on established criteria (5). Table 14.1 provides the major characteristics of T1D and T2D. Effective management involves use of self-monitoring of blood glucose, use of appropriate medications to regulate blood glucose levels, regular participation in physical activity (PA)/exercise, and body weight management as well as good dietary habits (5,68). Exercise interventions for individuals with diabetes should ideally involve a multidisciplinary team of specialists 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 (56).
Table 14.1 | Major Characteristics of Type 1 and Type 2 Diabetes |
Factor | Type 1 | Type 2 |
Age at onset | More often early in life but may occur at any age | Usually older than age 30 yr but may occur at any age |
Type of onset | Rapid, with short duration of symptoms in children; slower progression when onset occurs during adulthood | Slow progression (e.g., years) |
Genetic susceptibility | HLA-related DR3 and DR4, ICAs, IAAs; limited family history | Frequent genetic background; not HLA-related |
Environmental factors | Virus, toxins, autoimmune stimulation | Obesity, poor nutrition, physical inactivity, POP exposure |
ICA | Present at onset | Usually not observed |
Endogenous insulin | Minimal or absent | Stimulated response either adequate with delayed secretion or reduced but not absent; insulin resistance present |
Nutritional status | Thin or overweight; catabolic state (recent weight loss) | Obese, overweight, or normal; little or no recent weight loss |
Symptoms | Thirst, polyuria, polyphagia, fatigue | Mild or frequently none; acanthosis nigricans; PCOS in females |
Ketosis | Common at onset or during insulin deficiency | Unusual (resistant to ketosis except during infection or stress) |
Control of diabetes | Often difficult, with wide glucose fluctuation | Variable; helped by dietary adherence, weight loss, exercise |
Dietary management | Essential but must be balanced with insulin dosage | Essential; may suffice for glycemic control |
Insulin | Required for all | Used by ~40% |
Oral or injected antihyperglycemic medications | Usually minimally effective (unless insulin resistant as well) | Effective |
HLA, human leukocyte antigen; DR, D-related antigen; ICA, islet cell antibody; IAA, insulin autoantibodies; POP, persistent organic pollutants; PCOS, polycystic ovary syndrome.
Precise hormonal and metabolic events that normally regulate glucose homeostasis are frequently disrupted in diabetes because of defects in insulin release, action, or both (5). Glucose control requires near-normal balance between hepatic glucose production and peripheral glucose uptake, combined with effective insulin responses (76). With diabetes, a reduced ability to precisely match glucose production and utilization results in daily glucose fluctuations and requires adjustments in dosages of exogenous insulin and/or antihyperglycemic medications (Table 14.2). These adjustments should be combined with adequate changes in dietary intake, particularly when anticipating exercise (85).
Table 14.2 | Risk of Hypoglycemia with Use of Diabetes Medications |
No or Minimal Risk | Higher Risk |
Acarbose: Precose® Metformin and combinations with metformin: Glucophage® Avandamet® (metformin/rosiglitizone) Miglitol: Glyset® Pioglitazone: Actos® Rosiglitizone: Avandia® Bromocriptine: Cycloset® Albiglutide: Tanzeum Dulaglutide: Trulicity Exenatide: Byetta® (daily) Bydureon™ (weekly) | Glimepiride: Amaryl® Glipizide and combinations with glipizide: Glucotrol®, Glucotrol XL® MetaGlip (glipizide/metformin) Glyburide and combinations with glyburide: DiaBeta Glynase® PresTab® Micronase® Glucovance® (glyburide/metformin) Nateglinide: Starlix® Repaglinide: Prandin® Insulin: All types and delivery methods |
Liraglutide: Victoza® Alogliptin: Nesina/Galvus Linagliptin: Tradjenta Linagliptin and empagliflozin: Glyxambi Sitagliptin: Januvia® Saxagliptin: Onglyza® Pramlintide: Symlin® Canagliflozin: Invokana® Dapagliflozin: Farxiga® Empagliflozin: Jardiance |
Well-known brand names are listed following the generic names. Always consider new diabetes medications that may not be listed and medications prescribed for diabetes complications or other conditions.
Reprinted with permission from Colberg S. Chapter 17: Exercise prescription. In: Mensing C, editor. The Art & Science of Diabetes Self-Management Education Desk Reference. 4th ed. Chicago (IL): American Association of Diabetes Educators; 2017. p. 888.
After diagnosis, clinical emphasis is placed on self-monitoring of blood glucose, which benefits glycemic control regardless of the type of diabetes. Adjustments to insulin dose, oral medications, and/or carbohydrate intake can be fine-tuned using the detailed information provided by continuous glucose monitoring (62).
Concomitant lifestyle improvements (i.e., dietary changes and exercise) assist in the control of blood glucose levels and reduce the risk of acute and long-term diabetes-related complications (6). Overall glycemic control is assessed by measuring HbA1C, which reflects a time-averaged blood glucose concentration over the previous 2–3 months. The recommended HbA1C goal is <7.0% (7). Using the estimated average glucose conversion, this goal equates to <154 mg ∙ dL−1 (or 8.6 mmol ∙ L−1). HbA1C levels should ideally be assessed every 3–4 months (7).
Regular exercise facilitates improved blood glucose control in T2D (39,52,55,64,74). Although regular exercise does not uniformly provide glycemic management in those with T1D unless appropriate regimen changes are made, exercise is still considered a safe and effective adjunct therapy for the management of T1D (79). Exercise, in combination with dietary improvements and weight loss, has been demonstrated to favorably modify lipids and lipoproteins, thereby lowering cardiovascular disease (CVD) risk in diabetes (64). Also, reductions in BP have been demonstrated through exercise and weight loss and may be partially explained by improved insulin sensitivity and loss of visceral fat (67). Glucose control is improved through exercise in individuals with T2D. A lower HbA1C generally reduces the risk for diabetes-related complications, including CVD (14,66,86). Table 14.3 summarizes benefits of chronic exercise for individuals with T1D and T2D.
Table 14.3 | Effects of Exercise in Diabetes |
Parameter | Type 1 | Type 2 |
Cardiovascular | ||
Aerobic capacity or fitness level | ↑ | ↑/↔ |
Resting pulse rate and rate–pressure product | ↓ | ↓ |
Resting systolic BP (in mild-to-moderate hypertension) | ↓ | ↓ |
HR at submaximal loads (aerobic only) | ↓ | ↓ |
Lipid and lipoprotein alterations | ||
HDL-C | ↑ | ↑ |
LDL-C | ↓/↔ | ↓/↔ |
VLDL-C | ↓ | ↓ |
Total cholesterol | ↔ | ↔ |
Cardiovascular risk ratio (total cholesterol/HDL) | ↓ | ↓ |
Anthropometric measures | ||
Body mass (aerobic exercise in particular) | ↓/↔ | ↓ |
Fat mass (including visceral fat) | ↓ | ↓ |
Fat-free mass (resistance exercise mainly) | ↑ | ↑/↔ |
Metabolic parameters | ||
Insulin sensitivity and glucose/fat metabolism | ↑ | ↑ |
HbA1C (overall glycemic control) | ↓/↔ | ↓ |
Postprandial thermogenesis or thermic effect of food | ↑ | ↑ |
Presumed psychological outcomes | ||
Self-concept and self-esteem | ↑ | ↑ |
Depression and anxiety | ↓ | ↓ |
Stress response to psychological stimuli | ↑ | ↑ |
HR, heart rate; VLDL-C, very low density lipoprotein cholesterol; ↑, increase; ↓, decrease; ↔, no change.
Acutely uncontrolled diabetes is a relative contraindication to exercise participation. Self-monitoring of blood glucose before and after exercise is essential, especially in insulin users, to allow individuals to make appropriate adjustments in insulin or other medications and food intake (29,68). Although light-intensity exercise will expend calories and assist with weight maintenance, it will likely lower blood glucose levels less than moderate-intensity workouts. Conversely, vigorous exercise may result in transient hyperglycemia because glucose production tends to increase more than glucose use (65,71). Thus, two common risks associated with exercise in individuals with diabetes are hypoglycemia and hyperglycemia; however, practical precautions can be taken to reduce the risk or avoid their onset.
Case Study 14-1 Quiz: |
Description, Prevalence, and Etiology 1. What health benefits is Mrs. Case Study-DM likely to experience from becoming and staying regularly physically active? Are the benefits different for people with T2D versus T1D? |
 | Preparticipation Health Screening, Medical History, and Physical Examination |
The ACSM’s Guidelines for Exercise Testing and Prescription (GETP) (3) evidence-based model for preparticipation health screening for those with T1D and T2D is based, in part, on the individual’s current level of exercise. Medical clearance rather than medical exams/graded exercise testing is only recommended, and the decision to include these tests is left to the health care provider. For exercise more vigorous than brisk walking or exceeding the demands of everyday living, sedentary and older individuals with diabetes may benefit from being more thoroughly assessed for conditions that are associated with a higher risk of CVD (including uncontrolled hypertension), contraindications to exercise, or diabetes-related factors that may predispose them to injury (e.g., autonomic neuropathy, peripheral neuropathy, a history of foot lesions, and untreated proliferative retinopathy) (6,22). Preexercise assessments may include a symptom-limited exercise test depending on the age of the person, diabetes duration, and the presence of additional CVD risk factors (22).
The best protocol for screening asymptomatic individuals with diabetes for coronary artery disease remains unclear, and routine screening is not recommended (6). Although a symptom-limited exercise test may be done, it may not be necessary in young individuals with diabetes and those with a low risk of CVD. Specific indications for a symptom-limited exercise test are shown in Box 14.1. Following these criteria will avoid automatic inclusion of lower risk individuals with diabetes and advise such testing primarily for previously sedentary individuals who plan to engage in exercise more intense than normally undertaken during activities of daily living. Although a symptom-limited exercise test may be used for exercise prescription and risk stratification, its comprehensive use to diagnose myocardial ischemia in asymptomatic individuals is not recommended. A recent meta-analysis suggested that systematic detection of silent ischemia in high-risk, asymptomatic patients with diabetes is unlikely to provide any major benefit in individuals whose cardiovascular risk is controlled by an optimal medical treatment (51).
Indications for Symptom-Limited Exercise Testing Prior to Vigorous Exercise Participation | |
Individuals with diabetes and at least one of the following:
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Any of the following, regardless of age:
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Brown RJ, Wijewickrama RC, Harlan DM, Rother KI. Uncoupling intensive insulin therapy from weight gain and hypoglycemia in Type 1 diabetes. Diabetes Technol Ther. 2001;13:457–60; and Brown SJ, Handsaker JC, Bowling FL, Boulton AJ, Reeves ND. Diabetic peripheral neuropathy compromises balance during daily activities. Diabetes Care. 2015;38:1116–22.
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