Exercise and Diabetes. Sheri R. Colberg

in Point: Continued

      Before starting his supervised aerobic exercise training, AB is advised by his personal trainer to have a checkup with his health-care provider to assess his overall health, diabetes control, and potential for cardiovascular and other diabetes-related complications. At that appointment, he obtains the following results:

      Resting Measurements

      Height: 70 inches

      Weight: 196 lb

      BMI: 28.1 (overweight)

      Waist circumference: 41 inches

      Heart rate: 74 beats per minute (bpm)

      Blood pressure: 128/80 mmHg

      Fasting Labs

      Fasting plasma glucose: 120 mg/dl

      A1C: 6.3%

      Total cholesterol: 150 mg/dl (on medication)

      Triglycerides: 100 mg/dl

      High-density lipoprotein cholesterol: 45 mg/dl

      Low-density lipoprotein cholesterol: 85 mg/dl

      Even though his diabetes appears to be well controlled and despite not having any cardiovascular symptoms, AB’s physician recommends that he undergo a graded exercise stress test before starting intense exercise, to rule out the possibility of coronary artery disease, given his elevated number of cardiovascular risk factors: older age, diabetes for >10 years, waist circumference, history of elevated cholesterol levels, and a family history of heart disease (AC’s father died at age 54 years from a heart attack).

      The results of AB’s maximal treadmill test (with 12-lead electrocardiogram) are normal, with no evidence of coronary ischemia during the test and no arrhythmias noted. His maximal blood pressure reaches 220/85, and his maximal heart rate is 154 bpm (expected age-based maximal heart rate of 162 bpm). His maximal oxygen consumption (VO2) is 21.2 ml/kg/min (milliliters of oxygen per kilogram of body weight per minute), which is low based on norms for his age (58 years) and sex (male).

      Exercise Program Goals

      Activity: AB starts his exercise training program with his personal trainer after all testing has been completed by undertaking treadmill walking, as desired. In addition, he plans to continue golfing as many weekends as possible for 3–4 h at a time to maintain a higher level of unstructured activities.

      Intensity, Frequency, and Duration: On the advice of his personal trainer, AB initially undertakes only 20 min of moderate-intensity treadmill walking done at 50% of his heart rate reserve (HRR; which for him, is a target HR of 114 bpm; see chapter 4 for details about how to prescribe exercise intensity using this method), 3 days per week. His goal is to work up to doing intense exercise (at 75% of his HRR, or a target HR of 134 bpm) for at least 30 min at a time.

      Progression: For the first 2–3 weeks of training, AB progresses by first increasing the intensity of his training up to his target (by aiming for a HR that is 5–10 bpm higher each subsequent week), and after another 2 weeks he increases his exercise time by 5 min a week until he reaches 30 min of continuous, intense walking for each of his thrice-weekly exercise sessions. He continues this program for 12 weeks total, at which point he plans to add in twice-weekly sessions of resistance work.

      Exercise Goals: His long-term exercise goal is to complete a minimum of 90 min of vigorous aerobic exercise weekly, along with another 90 min of moderate-to-intense resistance training. (Continued)

      PRE-EXERCISE STRESS TESTING TO DETECT CARDIOVASCULAR DISEASE

       Low-Intensity Training

      For individuals who wish to participate in low-intensity activities like walking, physicians and other health-care providers should use clinical judgment in deciding whether to recommend pre-exercise testing (Colberg 2010). Conducting exercise stress testing before walking that does not exceed the cardiovascular demands of an individual’s usual activities of daily living may not be routinely necessary as a diagnostic tool for cardiovascular disease, and requiring it may create barriers to participation in all physical activities. Moreover, current guidelines avoid automatic inclusion of lower-risk individuals in graded exercise testing requirements, given that their risk of a false-positive test is higher and may outweigh the benefits of detection of cardiovascular abnormalities (Colberg 2011).

       Higher-Intensity Training

      For exercise more vigorous than brisk walking or exceeding the demands of everyday living, it remains unclear whether sedentary and older individuals with type 1 diabetes (T1D) or T2D will benefit from undergoing graded exercise testing or other types of routine cardiovascular testing (Bax 2007). Depending on the individual’s age, diabetes duration, and presence of additional cardiovascular risk factors or diabetes-related complications, however, the risks associated with conducting such testing may be justified when it can reveal underlying pathologies that potentially affect either the safety or efficacy of more intense exercise participation.

      The prevalence of symptomatic and asymptomatic coronary artery disease is greater in individuals with T2D (Kothari 2002, Eddy 2008), and maximal graded exercise testing can identify a small proportion of asymptomatic people with severe coronary artery obstruction (Curtis 2010). Although the latest ADA Standards of Medical Care state that the need for screening asymptomatic diabetic patients for coronary artery disease remains unclear (Bax 2007, ADA 2013), graded exercise stress test with electrocardiogram (ECG) may be indicated for diabetic individuals to detect cardiovascular disease based on the criteria in Table 2.1 (Colberg 2010). Providers should use clinical judgment in this area. Certainly, high-risk patients should at least be encouraged to start physical activity participation with short periods of low-intensity exercise and to increase the intensity and duration slowly.

      Table 2.1 Criteria for Consideration of Graded Exercise Stress Testing

Age >40 years, with or without cardiovascular disease risk factors other than diabetes

Age >30 years and • T1D or T2D of >10 years’ duration • Hypertension • Cigarette smoking • Dyslipidemia • Proliferative or preproliferative retinopathy • Nephropathy, including microalbuminuria

Any of the following, regardless of age • Known or suspected coronary artery disease, cerebrovascular disease, or peripheral vascular disease • Autonomic neuropathy • Advanced nephropathy with renal failure

       Risk Assessment

      The UKPDS Risk Engine (www.dtu.ox.ac.uk/riskengine/index.php) (Stevens 2001) may be used to calculate expected 10-year cardiovascular risk based on age, sex, smoking, A1C levels, diabetes duration, lipids, blood pressure, and race or ethnicity. Most young individuals with a low risk of coronary artery disease are not likely to benefit from pre-exercise stress testing done with the primary intent of detecting coronary artery disease, particularly given that the lower the coronary artery disease risk, the higher the chance of having a false-positive test (Stevens 2001, Fowler-Brown 2004). In the Look AHEAD (Action for Health in Diabetes) trial, although exercise-induced abnormalities were present in 22.5% of the >1,000 study participants, only greater age was associated with increased prevalence of all abnormalities during maximal exercise testing (Curtis 2010).

       Testing of Higher-Risk Individuals

      Symptomatic individuals may benefit from diagnostic cardiac stress testing, both for diagnostic purposes and to assist in safe and effective exercise prescription that avoids exacerbating pre-existing cardiac limitations during exercise (such as an ischemic threshold). For those with known or suspected coronary artery disease, the clinical value of a noninvasive exercise stress test may be better ascertained primarily by stratifying subjects into either low- or high-risk groups based on the number of cardiac risk factors, family history, and current symptoms

      (Curtis 2010). For asymptomatic