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Chapter 2 Pre-Exercise Evaluation and Assessment

A safe and effective exercise program for people with diabetes minimizes the acute risks and long-term complications associated with physical activity while maximizing the benefits (Bernbaum 1989, Gilchrist 2000, Seeger 2011). As the benefits frequently outweigh the risks, regular participation in a variety of physical activities should be recommended and encouraged for almost all individuals with diabetes, keeping in mind that certain comorbidities (whether diagnosed or not) may carry a higher risk than others.

Case in Point: Pre-Exercise Screening, Cardiovascular Risk, and Disease Detection

AB is a 58-year-old man who has had type 2 diabetes (T2D) for ~10 years and is interested in starting a new exercise training program at a local community center. The exercise that he intends to do revolves around a program of aerobic exercise on a treadmill at an intensity equal to ~75% of his heart rate reserve (see chapter 4 for more information on prescribing exercise intensity), which is considered a vigorous physical activity—that is, more intense than his normal daily walking pace (i.e., brisk walking). Although he has engaged in several exercise training programs off and on over the past few years, his most consistent physical activity currently is playing golf on most weekends (which includes walking and carrying his clubs). His only medications are metformin (used to control morning hyperglycemia) and a lipid-lowering drug to reduce cholesterol levels.

Questions to Consider

1. Should AB schedule an appointment with his primary physician or other health-care provider for a pre-exercise medical evaluation and examination?

2. Does AB need to undergo a graded exercise stress test before participation in his planned exercise intensity?

(Continued)

MEDICAL SCREENING AND EXAMINATION

Ideally, most individuals diagnosed with diabetes should consult a health-care provider before beginning an intense physical fitness program (Colberg 2010, 2011). An absolute requirement to do so before participation in all types of physical activity should not be uniformly enforced, however, as it may prevent individuals from gaining any of the health and psychological benefits associated with being normally physically active, such as undertaking brisk walking as part of their activities of daily living.

Screening for Diabetes-Related Complications

Given that exercise participation can be complicated by the presence of diabetes-related health complications (Sigal 2004), before undertaking new higher-intensity physical activity, individuals are strongly advised to undergo a detailed medical evaluation and screening for acute and chronic blood glucose control, physical limitations, medications, and macrovascular and microvascular complications associated with the heart, blood vessels, eyes, kidneys, feet, and nervous system (Colberg 2010). A medical examination conducted before undertaking a new physical activity or fitness program can include determination of the presence of diabetes-related (or other) comorbidities (e.g., cardiovascular disease, neuropathy, nephropathy, and retinopathy) that can affect an individual’s ability to undertake certain types of physical training, increase cardiovascular risk, or predispose them to injuries (Sigal 2004, 2006; Colberg 2010). Certain conditions may be contraindicated or predispose individuals to injury, such as uncontrolled hypertension, severe autonomic neuropathy, severe peripheral neuropathy or history of foot lesions, and unstable proliferative retinopathy. The individual’s age and previous physical activity level also should be considered (American Diabetes Association [ADA] 2013). Such health considerations should be factored into an exercise prescription for it to be both safe and effective.

Physical Examination

Minimally, starting body weight, heart rate, and resting blood pressure ideally should be assessed before exercise participation. In addition, inspection of the lower extremities for edema and the presence of arterial pulses is recommended, along with tests of neurological function, especially if the individual has prescribing prior bouts of dizziness or faintness during or following physical exertion. Given that such symptoms could result from any number of conditions, including autonomic dysfunction, cardiovascular insufficiency, medication use, or dehydration, among others, a determination of the cause (if possible) is helpful in prescribing appropriate physical activity regimens. Likewise, a visual inspection of the feet and lower extremities can reveal any contraindications to weight-bearing exercise, including unhealed ulcerations. A history of falls is also clinically relevant, given that certain exercise interventions like balance training have been shown to lower the risk of falling in people with T2D (Morrison 2010). Finally, the health-care or fitness professional should be made aware of any orthopedic or other limitations (like prior joint surgery) that might affect exercise prescription for the individual.

Case 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 patients with diabetes, however, identification of cardiovascular risk factors and risk stratification may assist health-care providers in justifying the use of graded exercise testing, but is not currently recommended (Bax 2007). In any case, all decisions regarding the necessity of such testing should attempt to more effectively target the select individuals at higher risk for underlying cardiovascular disease (Sigal 2004). For example, individuals with silent myocardial ischemia have a poorer prognosis than those with normal stress tests,

and their risk is further accentuated if cardiac autonomic neuropathy coexists

(ADA 2013).

Use of Stress Testing to Detect Ischemia

A systematic review for the U.S. Preventive Services Task Force (2004) concluded that stress testing should not be routinely recommended to detect ischemia in asymptomatic individuals with a low coronary risk (<10% risk of a cardiac event over 10 years) because the risks resulting from the invasive testing done after a false-positive test outweigh the benefits of detection (Fowler-Brown 2004). Individuals who exhibit nonspecific electrocardiograph changes in response to exercise or who have nonspecific ST- and T-wave changes at rest may need follow-up testing. The Detection of Ischemia in Asymptomatic Diabetics (DIAD) trial involving 1,123 individuals with T2D and no symptoms of coronary artery disease, however, found that screening with adenosine-stress radionuclide myocardial perfusion imaging for myocardial ischemia over 4.8 years did not alter rates of cardiac events (Young 2009). Therefore, the cost-effectiveness and diagnostic value of more-intensive testing remain in question (Sigal 2004, 2006; Colberg 2010).

Case in Point: Event Discussion

At the end of 12 weeks of intense aerobic training and just before starting his resistance workouts, AB is being instructed on the use of the resistance equipment by his personal trainer when he falls to the floor following a short cardio warm-up and goes into full cardiac arrest within 5 min. The community center houses an automated external defibrillator (AED), which his personal trainer brings to his side while a concerned onlooker calls 911 to summon emergency medical assistance. The AED indicates that AB needs cardioversion, and his trainer initiates the shock that restarts AB’s heart before the paramedics arrive on the scene from a nearby fire station another 5 min later.

Following this event AB is hospitalized, but no myocardial damage is found. His cardiac arrest is determined to have been caused by a potentially fatal arrhythmia (ventricular fibrillation), which was found after later review of the rhythm recorded by the AED during the event. Upon further examination by a cardiologist, AB is found to have 100% blockage of one of his primary coronary vessels (left anterior descending) but appears to have developed collateral circulation there, likely as the result of the vigorous exercise training program that he undertook before having this event, which prevented any infarction of the myocardium in the area fed by that vessel. Thus, it is decided that his cardiac arrest was simply caused by the arrhythmia initiated by the agitated state of his heart as a result of the blockage. Following bypass surgery, he is released from the hospital and cleared to participate in cardiac rehabilitation after a few weeks.

Additional Questions to Consider

1. Should the pretraining medical and exercise stress testing have been able to detect AB’s coronary artery disease before it became potentially fatal?

2. Is there another form of testing that AB should have undergone before starting his training?

3. Did the intense exercise training actually help or hurt AB, given his undiagnosed cardiovascular disease?

(Continued)

Testing of Low-Risk Individuals for Fitness Assessment

Although graded exercise testing currently is advised primarily for previously sedentary people with diabetes who want to undertake activity more intense than brisk walking to assess cardiovascular risk (Sigal 2006, Colberg 2010), in some cases, testing (with or without ECG monitoring of heart function) may be undertaken for other purposes. In addition to diagnosing or defining the prognosis of known cardiac disease, exercise stress testing is presently used to assess physical fitness, determine functional capacity, prescribe an exercise plan, and guide cardiac rehabilitation training. With these alternate assessments in mind, the aforementioned risk-based criteria do not exclude the possibility of conducting graded exercise stress testing on individuals with a low risk of cardiovascular disease or those who are planning to engage in less-intense exercise (Stevens 2001). In the absence of contraindications to maximal stress testing, it still can be considered for anyone with T1D or T2D who simply wants to assess his or her fitness level or use the maximal or peak results to determine appropriate exercise training intensities and other fitness goals. Although clinical evidence does not definitively determine who should never consider undergoing such testing, potential benefits should be weighed against the risk associated with unnecessary procedures for each individual, especially in individuals with a higher risk profile (Kothari 2002, Sigal 2004).

Pre–resistance Training Exercise Testing

As for resistance training, no studies have yet addressed whether pre-exercise stress testing is necessary or beneficial before participation in such activity. At present, most testing centers are equipped for maximal stress testing, but not for an alternate form of testing involving resistance exercise. Because coronary ischemia is less likely to occur during resistance compared with aerobic exercise eliciting the same heart rate, resistance exercise may not even induce ischemia in most individuals (Ghilarducci 1989, Featherstone 1993). A review of 12 studies of resistance exercise in men with known coronary artery disease reported no angina, ST-segment depression (indicative of coronary ischemia), abnormal hemodynamics, ventricular dysrhythmias, or other complications during such exercise (Wenger 1995).

Case in Point: Wrap-Up

AB was completely asymptomatic of coronary artery disease before this event, and it was not detected by a graded exercise test, which shows that this testing is not infallible and far from conclusive. Given his lack of any cardiac symptoms, it would not have been advisable—either from a medical standpoint or a financial one—to recommend or require additional, possibly more invasive, testing of his cardiovascular status before this event.

Finally, the intense exercise training that AB had completed before this event was completely appropriate under the circumstances and, in fact, it likely helped save his life by stimulating the growth of new, collateral vessels that prevented myocardial damage despite full blockage of a crucial coronary artery feeding the left ventricle. Effectually, his exercise participation saved his life twice: once by stimulating the growth of new collateral circulation to his heart and again by placing him in a facility that had an AED available to treat him during his event. AB later said to his personal trainer that had his event occurred on the golf course, where he had spent the whole day before, he likely would not have survived it.

For most people with diabetes, low-level physical activities can be undertaken without the need for a medical exam or graded exercise test that potentially could create barriers to participation. In some cases, however, higher-risk individuals desiring to undertake moderate- or vigorous-intensity exercise training may benefit from undergoing a medical evaluation and possible stress testing with ECG before participation to diagnose pre-existing cardiovascular problems that may make such training more risky.

Professional Practice Pearls

• Most individuals diagnosed with diabetes should consult a health-care provider before beginning an intense physical activity program, but an absolute requirement to do so in all cases would create unnecessary barriers to participation in low-level activities.

• Before undertaking new higher-intensity physical activity, providers may use their judgment in recommending whether individuals with any type of diabetes should undergo a detailed medical evaluation and screening.

• For individuals wishing to participate in low-intensity activities only, pre-exercise testing is likely not beneficial, and providers should use their clinical judgment in deciding whether to recommend it.

• Graded exercise testing should not be routinely recommended to detect ischemia in asymptomatic individuals with a low coronary risk because the risks resulting from the invasive testing done after a false-positive test outweigh the benefits of detection.

• Symptomatic individuals may benefit from diagnostic cardiac stress testing, both for diagnostic purposes and also to assist in safe and effective exercise.

• To date, no studies have addressed whether pre-exercise stress testing is necessary or beneficial before participation in resistance training (although likely it is not).

• Graded exercise testing may be undertaken in low-risk and other individuals to determine fitness levels or to obtain testing results for effective exercise prescription.

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