Diet and Exercise Part 4

Exercise and longevity

Primary Prevention of Atherosclerosis

Exercise training can favorably modify many of the conditions associated with an increased risk of coronary artery disease, including hypercholesterolemia, elevated blood pressure, glucose intolerance, obesity, and the less firmly incriminated traits of hypertriglyceridemia, hyperinsulinemia, hyperfibrino-genemia, and psychological stress. Studies conducted in men, women, and children demonstrated a consistent inverse relation between physical fitness and body weight, percent body fat, systolic blood pressure, and serum levels of cholesterol, triglycerides, and glucose.116 In addition, exercise appears to reduce levels of C-reactive protein and other inflammatory markers of cardiovascular risk.

Is a sedentary way of life itself a risk factor independent of these other traits? Investigators at the Centers for Disease Control and Prevention (CDC) reviewed 43 methodologically sound studies of exercise and coronary artery disease.118 Collectively, these studies showed that sedentary living increases coronary risk by 1.9 times. An independent meta-analysis derived the same relative risk.119 The magnitude of this excess risk is similar to that conferred by other risk factors: hypertension, 2.1 times; hypercholesterolemia, 2.4 times; and cigarette smoking, 2.5 times.118 Because sedentary living is at least two to three times more prevalent than any of these other risk factors, it can be argued that physical inactivity makes the most significant contribution to the epidemic of coronary artery disease in the United States. Maintaining a physically active way of life can be expected to reduce the risk of myocardial infarction by 35% to 70%.


Although reductions in coronary artery disease account for the great majority of the improvements in survival conferred by exercise, other factors may play a role. Physical activity protects against stroke120 and reduces the risk of colon cancer.121 Exercise also reduces the risk of breast cancer122 and cancer of the reproductive organs in women, and very intensive exercise may reduce the risk of prostate cancer. Physical activity is associated with a reduced risk of age-related cognitive dysfunction123 and hip fractures.124 Current studies continue to confirm observations that have occurred over the past 50 years, demonstrating that there is a graded, inverse association between activity and mortality.

Secondary Prevention of Ischemic Heart Disease

Since the 1970s, interest in the potential role of exercise in the rehabilitation of patients after myocardial infarction and in the prevention of recurrent cardiac events has grown.127 Certain benefits of supervised exercise programs have been clearly established, including physiologic and symptomatic improvements and the reduction of risk factors. Patients completing exercise programs demonstrate the training effect, including a lower heart rate at rest and both a lower heart rate and a lower systolic blood pressure at submaximal work loads. These changes reduce myocardial oxygen demands, thereby increasing the angina threshold. Significant improvements in maximal oxygen uptake and work capacity can also be demonstrated. Exercise training can improve walking distances in patients with claudi-cation.128 Exercise can be useful even for patients with severe is-chemic left ventricular dysfunction and chronic congestive heart failure, although extra precautions should be taken in these patients. In addition, cardiac exercise programs are safe.129 Most centers note a substantial improvement in mental attitudes, a decrease in the use of medications, and widespread patient satisfaction. Most important, randomized trials demonstrate that cardiac exercise programs reduce mortality by 20% to 25%.129,130 Unsupervised moderate exercise, such as walking or gardening, also appears to reduce mortality in older patients with coronary artery disease.131

Prescribing exercise

Physicians can provide important incentives for their patients by educating them about the benefits, as well as the risks, of habitual exercise. Healthy, sedentary individuals are the largest group in need of such advice. In addition, physicians may be responsible for the medical screening of competitive athletes or for prescribing exercise for patients with chronic illnesses.

A careful history and physical examination are central to the medical evaluation of all potential exercisers. Particular attention should be given to a family history of coronary disease, hypertension, stroke, or sudden death and to symptoms suggestive of cardiovascular disease. Cigarette smoking, sedentary living, hypertension, diabetes, and obesity all increase the risks of exercise and may indicate the need for further testing. Physical findings suggestive of pulmonary, cardiac, or peripheral vascular disease are obvious causes for concern. A musculoskeletal evaluation is also important.

The choice of screening tests for apparently healthy individuals is controversial. A complete blood count and urinalysis are reasonable in all cases. Determination of blood glucose, serum cholesterol, and creatinine levels may also be useful in screening for risk factors or occult disease. The Valsalva maneuver and the isometric handgrip may be useful additions to the workup.

Young adults who are free of risk factors, symptoms, and abnormal physical findings do not require further evaluation. It is not at all clear that more aggressive medical screening can prevent sudden cardiac death. Although echocardiography and electrocardiography might reveal asymptomatic hypertrophic cardiomyopathy in some patients, the infrequency of this problem makes routine screening impractical.

The role of exercise electrocardiography as a screening test before an individual begins an exercise program is controversial. The AHA no longer recommends routine exercise testing for asymptomatic individuals.89 In fact, a study of 3,617 asymptomatic men 35 to 59 years of age casts doubt on the value of exercise electrocardiography for routine preexercise screening.132 None of the men had known coronary artery disease on entry into the study, but all were at increased risk because of hyper-cholesterolemia. Each individual had an exercise test on entry;the tests were repeated annually over a mean follow-up period of 7.4 years.

Table 6 Exercise Time Required to Consume 2,000 kcal

Activity

Time (hr)

Strolling

10

Bowling

8.5

Golf

8

Raking leaves

7

Doubles tennis

6

Brisk walking

5.5

Biking (leisurely)

5.5

Ballet

4.5

Singles tennis

4.5

Racquetball, squash

4

Biking (hard)

4

Jogging

4

Downhill skiing

4

Calisthenics, brisk aerobics

3.3

Running

3

Cross-country skiing

3

Exercise proved safe in this group, with approximately 2% experiencing exercise-related cardiac events. Only 11 of the 62 men who experienced such events had abnormal exercise tests on entry, a sensitivity of only 18%. The cumulative sensitivity of annual tests was also low (24%). Even in elderly people, routine exercise testing before starting a moderate exercise program may not be necessary.133


Despite its limitations as a screening test for silent coronary artery disease, exercise testing can be useful for detecting exercise-induced arrhythmias, establishing a maximal heart rate for the exercise prescription, and determining work capacity. Serial testing may help motivate a patient by demonstrating increased work capacity. Specialized tests such as pulmonary function tests and exercise ergometry, Holter or telemetric monitoring during exercise, and echocardiography may be very useful in the evaluation of patients who have known or suspected cardiovascular abnormalities.

Screened patients will fall into one of three groups:

1. Healthy persons who can exercise without supervision. (Medical guidelines [see below] may still be helpful.)

2. Patients with ischemic heart disease or other significant cardiovascular abnormalities who should have medically supervised, graded exercise programs. (If structured programs are not available, such patients should engage in milder forms of exercise, such as walking or bicycling, with appropriate precautions.)

3. Patients for whom physical exertion is contraindicated because of decompensated congestive heart failure, complex ventricular irritability, unstable angina, significant aortic valve disease, aortic aneurysm, uncontrolled diabetes, or uncontrolled seizure disorders.

People can exercise in the course of daily life or in formal exercise programs. Although most physicians have recommended structured exercise, recent studies demonstrate that even modest levels of physical activity are beneficial.131,134 Walking and gardening are good examples131,134,135; such activities are protective even if they are not started until midlife or late in life.136 In one study, for example, elderly men who walked less than 1 mile a day had nearly twice the mortality of men who walked more than 2 miles a day.137 Compliance with walking is good,138 and lifestyle interventions appear to be as effective as formal exercise programs of similar intensity in improving cardiopul-monary fitness, blood pressure, and body composition.139,140

People should be encouraged to exercise nearly every day. Formal, intense exercise is not necessary; even moderate exercise that consumes about 150 kcal/day or 1,000 kcal/wk is very beneficial to health. Warm-ups, stretches, and a graded increase in exercise intensity can help prevent musculoskeletal problems.

Whereas all people can benefit from moderate daily activity, additional benefit can be obtained from more intense exercise; people who consume about 2,000 kcal in exercise a week obtain the greatest reduction of cardiovascular risk and mortality125,141 [see Table 6]. On average, people can obtain optimal health benefits from about 30 minutes of intense exercise or 45 to 60 minutes of mild to moderate exercise a day.

Physicians who provide specific practical advice are most likely to motivate their patients to adopt better health habits, including diet and exercise [see Table 7].

The success of a structured fitness program depends on the frequency, duration, and intensity of exercise. At least three sessions a week are needed. An alternate-day schedule will help prevent muscle soreness, but as fitness improves, individuals should be encouraged to increase exercise sessions to five or even seven times a week. Each session consists of 15 to 60 minutes of continuous aerobic activity. Untrained individuals may not be able to sustain even 15 minutes at first, but they should be encouraged to progress slowly as they improve. Each exercise session should be preceded by a 5- to 10-minute warm-up period and followed by a 5- to 10-minute cool-down period; stretching, gentle calisthenics, and walking are ideally suited for this purpose. These same exercises are excellent for a 5- to 10-minute cool-down period.

The intensity of exercise can best be judged by the target heart rate. A heart rate of 60% to 85% of maximum is considered optimal for training. If an exercise test has not been performed, a maximal heart rate can be calculated by subtracting the patient’s age from 220. Unfit people should start at the lower end of the target heart rate range. Healthy people need not monitor pulse rate. Instead, they can adjust the intensity of effort to a talking pace: they are working hard but still able to talk to a companion without a sensation of dyspnea.

Table 7 Exercise Advice for Patients

Get a medical checkup before beginning a formal exercise program

Warm up before each exercise session, and cool down afterward with 10 minutes of stretching and light calisthenics

Start slowly and build up to 30 minutes of moderate to intense exercise or 45-60 minutes of mild to moderate exercise

Begin with aerobic-type exercise, and later add stretching exercises for flexibility and low-resistance weight training for strength

Exercise daily if possible, and alternate harder workouts with easier ones

Dress comfortably

Use good equipment, especially good shoes

Do not eat during the 2 hr before you exercise, but drink plenty of water before, during, and after exercise, particularly in warmer weather

Do not ignore aches and pains that may signify injury

Do not exercise if you are feverish or ill

Learn warning signals of heart disease, including chest pain or pressure, disproportionate shortness of breath, fatigue, sweating, erratic pulse, light-headedness, or even indigestion

Consider getting instruction or joining a health club

Many kinds of exercise can be used to attain fitness. Dynamic (i.e., isotonic or aerobic) exercises in which large muscle groups are used continuously in a rhythmic, repetitive fashion for prolonged periods are ideal. The energy requirements of various activities have been measured. An energy expenditure of 5 to 6 METs (metabolic equivalents) or more is desirable for exercise training (1 MET is equal to the energy expenditure at rest or equivalent to approximately 3.5 ml O2/kg body weight/min). Brisk walking, jogging, swimming, cross-country skiing, skating, bicycling, and vigorous singles racket sports all provide good conditioning. Sports that allow prolonged periods of inactivity, such as doubles tennis, golf, bowling, and baseball, are much less desirable for fitness.125 Activities requiring sudden bursts of intense isometric activity, such as weight lifting, provide little cardiovascular conditioning and are contraindicated for patients with hypertension or heart disease. Contact sports cannot be recommended for health.

Although physicians should encourage patients to choose the sports that appeal most to them, medical considerations may also be important. For example, swimming is particularly desirable for individuals who have various musculoskeletal problems, and it is also ideal for people who experience exercise-induced asthma (EIA). Walking and bicycling are ideal for older individuals or for anyone who is starting from a low level of fitness. Jogging can be recommended because it is convenient and because the participants can easily adjust intensity and duration upward as fitness develops. Most desirable of all is a balanced program containing a variety of activities that exercise different muscle groups. People who have several activities at their command find it easier to remain active despite constraints of climate, schedules, and minor injuries. Although aerobic exercise is most important for metabolic improvement and cardiovascular health, exercises for flexibility and strength should be part of a balanced fitness program.94 Stretching exercises promote flexibility and help prevent injuries. A stretching routine should be performed at least two to three times a week, but it is best when incorporated in the warm-up and cool-down periods that should surround aerobic exercise. Low-resistance strength training is important to preserve muscle mass and power in the face of the aging process; two to three sessions a week are ideal.

Complications of exercise

Reducing Risk of Injury and Complications

Physicians can minimize injuries and medical complications associated with exercise by educating patients about potential problems. Physicians should stress the need for such safety devices as helmets for biking, eye guards for squash and racquet-ball, and elbow and knee pads for roller-skating. Diet, weight control, stress management, smoking cessation, and other preventive health measures should be discussed [see CE:III Reducing Risk of Injury and Disease], as should the warning signs of cardiac disease and the precautions for exercising in cold or hot climates.

Medical Complications of Exercise

Exercise promotes health, but it can also have adverse consequences. In some cases, the physiologic adaptations to exercise produce changes that may be misinterpreted as pathologic; athlete’s heart is one example. In other cases, however, exercise can precipitate clinically important problems.

The cardiac complications of exercise include ischemia, infarction, and sudden death, often caused by rupture of an atherosclerotic plaque.142 These dire events are infrequent and can be minimized by proper patient screening and instruction [see Prescribing Exercise, above]. Exercise-induced cardiac events are less common in people who exercise regularly than in sedentary individuals.143 On balance, exercise is clearly beneficial for the heart.

The most common pulmonary complication of exercise is EIA, which usually responds well to treatment.144 A much less common problem that can mimic hypersensitivity disorders is exercise-induced anaphylaxis.

The gastrointestinal response to exercise may produce reflux, diarrhea, or bleeding, which is usually occult and transient. Women who exercise very strenuously may experience oligomenorrhea or amenorrhea; the menstrual dysfunction is reversible but may be accompanied by osteoporosis. With appropriate precautions, exercise is safe during pregnancy. Precautions are also in order for prevention of hypoglycemia in diabetics who exercise.

People who exercise regularly can experience increased plasma volume that produces hemodilution or pseudoanemia. True anemia is less common but may result from shortened red cell life span caused by vascular trauma or iron deficiency. Exercise can produce proteinuria or hematuria; both are benign but are indications for studies to rule out renal disease. In warm, humid weather, exercise can produce heat cramps, hy-perthermia, or heatstroke, all of which are preventable.

Exercise does not appear to cause or accelerate osteoarthri-tis.102 Acute muscle injury, manifested by transient elevation of creatine phosphokinase levels, is common, but exertional rhab-domyolysis is rare. Musculoskeletal problems, however, are the most frequent side effects of exercise.145 Overstress, overuse, or trauma is usually responsible. Poor technique, faulty equipment, or fatigue often contributes to injury. Soft tissue injuries such as sprains, strains, and tendinitis usually respond well to simple treatment regimens. The same is true of stress fractures. Primary care physicians can manage many of these problems, but more serious injuries may merit referral to a sports medicine facility.

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