Ross E. Andersen
Kerry J. Stewart
This chapter describes the health benefits of regular exercise and the major types of exercise, and provides practical information for helping individuals to engage in exercise. The role of exercise in the management of a number of chronic diseases is described in other chapters.
The health benefits of regular exercise are well documented (1). Increased levels of physical activity and exercise are associated with increased longevity and with a decreased incidence of coronary artery disease, serum lipid abnormalities, hypertension, metabolic syndrome, and non–insulin-dependent diabetes. Unfortunately, the scientific knowledge about the benefits of exercise among the public and health professionals has not translated into a more active population. Presently, only approximately 23% of adults in the United States engage in levels of activity sufficient to produce health benefits, and 40% do not participate in any regular physical activity (1). Activity levels remained essentially unchanged throughout the 1990s despite large-scale public health education campaigns. Furthermore, people with chronic disease are more likely to report a sedentary lifestyle (2), as are minorities and individuals in lower socioeconomic classes (3). It is estimated that less than 30% of individuals at high risk for cardiovascular disease receive physical activity counseling during ambulatory care visits (4). By adding a sedentary lifestyle to its list of controllable risk factors for coronary artery disease, the American Heart Association has made regular exercise a major focus for preventive medicine (5).
The physical activity goal in Healthy People 2010 report by the Centers for Disease Control and Prevention (CDC) is to increase the proportion of adults who engage in regular exercise, preferably daily moderate activity for at least 30 minutes each day (6). This goal matches the Surgeon General's 1996 recommendation that all Americans should accumulate at least 30 minutes of activity throughout the day on most days of the week (1). It should be noted that those meeting these standards might derive additional health and fitness benefits by further increases in frequency or intensity of exercise.
Overall Health Benefits of Exercise
Several recent studies reaffirm a dose–response relationship between the amount of physical activity performed and health risk (7). Thus, the most fit and active individuals generally have the best risk profiles and reduced levels of early mortality and morbidity from a variety of diseases. For example, men and women who were healthy but less fit by treadmill testing had a higher risk of death from any cause over an 8-year followup compared with those who were moderately or highly fit (8). Data from the Nurse's Health Study found that physical inactivity of less than 3.5 hours per week and excess body weight (defined as a body mass index of 25 or higher) accounted for 31% of all premature deaths, 59% of deaths from cardiovascular disease, and 21% of deaths from cancer (9). We recently reported that exercise-induced reductions in total and abdominal obesity after 6 months of training were associated with favorable changes in risk factors for cardiovascular disease and diabetes, including those that constitute metabolic syndrome (7). Crespo et al. found that Puerto Rican men in the middle of the physical activity distribution had a 32% to 37% reduction in risk for all-cause mortality (10). Moreover, compared with the most sedentary fourth of participants, the next most active quartile had an accumulated survival that was approximately 3 years longer.
Most epidemiologic studies confirm significant risk reduction from achieving at least moderate intensity physical activity on most days of the week compared with those who are sedentary (8,11,12). Further increases in fitness produce relatively modest additional benefits. Thus, individuals do not need to attain high levels of fitness to accrue substantial health benefits from exercise (13).
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Effect of Changing Fitness Levels on Risk Profiles
Several studies have examined the effects of changing activity levels and its impact on all-cause mortality. Paffenbarger (12) reported that men who were initially sedentary but who started to participate in moderately vigorous sports had a 23% lower risk of death than those who remained inactive. Interestingly, improving any of four risk indicators (smoking, obesity, hypertension, physical inactivity) appeared to have the same relative impact on risk reduction. Gregg et al. (13) confirmed that older women who became active or who maintained activity levels, had an approximately 60% the risk of death compared to those who remained inactive. Each of these studies provides a strong rationale for encouraging sedentary patients to become more active.
Muscular and Cardiovascular Effects of Exercise
The body responds and adapts to the kind and amount of physical demands placed on it. The response is specific, meaning that the greatest changes are observed only in the areas on which demands are placed. For exercise to bring about an improvement in physical fitness, it must overload the muscles or organ system involved in the exercise. To overload is to exercise at a greater intensity than the intensity to which one is accustomed. The overload must be applied gradually, in stages, for maximal effectiveness and safety. Threshold of training is the amount of exercise that must be done to produce fitness improvements.
A consequence of the above principles is that the type of exercise engaged in must match the body function one wants to improve. Thus, if the objective is to improve cardiovascular endurance, exercise that increases heart rate and peripheral oxygen consumption is required. If the objective is to improve strength, exercise with increasing amounts of resistance is required. There is little carryover of the effects of an exercise from one component of fitness to another.
The factors that must be considered when establishing a comprehensive plan for physical conditioning differ for each of three types of exercise described below: cardiovascular conditioning, moderate-intensity exercise, and resistance exercise.
Vigorous Exercise Leading to Cardiovascular Conditioning
Vigorous exercise, with the goal of attaining the physiologic adaptation known as the conditioning effect, is beneficial for healthy people and selected patients with most chronic diseases. Moderate-intensity exercise that does not produce a full conditioning effect is also associated with health benefits (see below). Cardiovascular principles related to vigorous exercise are described here. The importance of stretching exercises and of not increasing the stress on the musculoskeletal system too rapidly is described in Chapter 68.
Aerobic Activities
Activities for cardiovascular fitness entail rhythmic repetitive movements of large muscle groups against small resistance. Such activities can be performed for a relatively long time. They include walking, jogging, swimming, cycling, rowing, jumping rope, skating, running, and cross-country skiing. These activities increase the demand for oxygen, and the muscles adapt by enhanced extraction of oxygen, which is the reason they are called aerobic activities. They are also called dynamic activities.
The principal hemodynamic adaptation to aerobic exercise takes place in the peripheral vascular and muscular systems. There is a better distribution of the cardiac output to exercised muscle groups, and those trained muscles can extract more oxygen from a given amount of blood flow. In the conditioned individual, heart rate and blood pressure are lower at rest and at a given submaximal workload. As a result, the conditional patient can do more work with less cardiac effort (i.e., less myocardial oxygen demand). In healthy people who practice aerobic exercise there are also changes in the heart itself, including increase in diastolic volume, increase in ejection fraction at rest and to a greater extent during exercise, and enhanced contractility.
Metabolic equivalents (METs) are used to rate the energy requirement of different physical activities, as indicated by the amount of oxygen extracted during those activities. One MET is 3.5 mL O2per kg body weight per minute and is equivalent to oxygen requirement at rest; 2 METs are twice the resting requirements, and so on. Table 16.1 shows the METs required for a broad range of activities. The higher the MET level attained during exercise, the more fit the patient is considered to be.
Intensity
Exercise intensity is set at a level that requires more effort than normal activity. This level is usually set at 70% of predicted maximal oxygen uptake, a level that is attained when the heart rate reaches approximately 80% of the age-predicted maximal rate. Maximum heart rate is estimated by subtracting age from 220. Optimal conditioning occurs when a person sustains this rate during an aerobic activity.
Duration
Exercise must be performed for a sufficient amount of time to be effective. To attain conditioning using vigorous
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exercise, duration should be at least 20 minutes at the target heart rate. Duration can be varied by increasing the distance covered at the same rate, such as in walking or jogging, or by reducing the rest time during a rest period. Studies in exercise physiology suggest that the total work done during an exercise session (i.e., duration × intensity) may be more important in eliciting improvements than intensity or duration alone. Consequently, a long, moderate-intensity workout in which heart rate reaches 40% to 60% of the age-predicted maximum may be equivalent to a shorter high-intensity workout if the total work is the same. A long, moderate-intensity workout (e.g., a long period of sustained walking) may be more suitable for beginners and for middle-aged or older patients because it reduces the risk of injury.
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TABLE 16.1 Energy Requirements of Certain Activities |
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Frequency
This factor refers to the number of times per week exercise is to be done. Exercise must be performed regularly, and for most types of exercise three to five times per week is desirable. However, two to three times per week is probably more sensible for the beginner because musculoskeletal injuries can occur at the start of a program from overuse. Exercise can then be increased to three to five times per week as adaptation takes place.
Hormonal and Metabolic Effects
In addition to the effect of training on the cardiovascular and muscular systems, aerobic exercise is associated with
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beneficial changes in a number of other systems. There is increased vagal tone, lowering of catecholamines, decrease in serum triglycerides, increase in the ratio of high- to low-density lipoprotein, a reduction in insulin resistance, reduction in total and abdominal adipose tissue, slowing of loss of bone mass, augmentation in plasma fibrinolytic activity, and enhanced endogenous opiate activity (may add to sense of well-being). A comprehensive review (see Peterson, http://www.hopkinsbayview.org/PAMreferences) distinguishes exercise (planned, structural, repetitive physical activity that leads to physical conditioning) from all other physical activity and summarizes benefits and risks that accompany both and the specific instructions that can be given to patients.
Initiating a Vigorous Exercise Program
Healthy people can develop their own physical conditioning program, using a self-instruction program (see references in Table 16.2). The objective of conditioning programs is to reach an exercise level at which the body achieves 70% of maximal predicted oxygen uptake, a level that is attained when the heart rate reaches approximately 80% of the maximal predicted rate (see Intensity). As stated previously, optimal conditioning in healthy people occurs with aerobic activity at the target heart rate for 20 minutes at least three times per week. Lower levels of aerobic exercise also produce a partial conditioning effect in healthy people.
Selected people should consult their health care practitioners before beginning a vigorous exercise program. For those at moderate risk or higher, such as men age 45 years and older, women age 55 years and older, and those with major risk factors for atherosclerosis, the American College of Sports Medicine recommends a medical history and physical examination, including an exercise stress test, prior to initiating a vigorous exercise program (14). Although not strongly evidenced based (15), Table 16.3 provides a summary of candidates for whom exercise stress tests should be considered. Nondiagnostic fitness tests for apparently healthy people are usually available at health clubs, YMCAs, wellness centers, and community colleges.
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When supervised and interpreted by qualified allied health professionals, these tests can provide the basis for the exercise prescription. Fees are usually nominal and are included in the overall package for exercise sessions.
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TABLE 16.2 Suggested Patient Readings |
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TABLE 16.3 People for Whom Stress Testing Should Be Considered when Beginning Vigorous Exercise Programs |
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Long-Term Maintenance of Cardiovascular Conditioning
Long-term compliance with formal exercise programs is often poor. It is necessary to exercise regularly at the proper intensity, frequency, and duration if physical fitness is to be maintained. Measurable deterioration in the conditioning effect occurs after missing only a few weeks. The time required to retrieve lost ground seems to be directly related to the length of time without exercise and the degree of physical fitness achieved before cessation of exercise.
Moderate-Intensity Exercise
For years, exercise scientists recommended that for exercise to “count,” it had to be performed at an intensity, duration, and frequency described above as “vigorous, continuous exercise leading to cardiovascular conditioning.” Although most people recognize that regular exercise plays an important role in promoting a healthy lifestyle, the sedentary majority do not participate in activity as suggested. Many do not enjoy it, or do not prioritize it highly enough to allocate time for it, or are limited by orthopedic or musculoskeletal problems. However, a number of studies show that many of the health benefits of physical activity can be obtained from less-intense exercise (e.g., activities such as those that require 3 to 5 METS, as listed in Table 16.1). Both the accumulation of bouts of activity throughout the day and a single extended exercise session can benefit health. For example, a recent study found that women in weight-loss programs who accumulated a series of short bouts of exercise throughout the day had slightly greater weight loss than those who exercised for the same total amount of time daily in one continuous session (16). Persons with sedentary occupations may find it easier to fit these shorter bouts of lifestyle activities into their busy schedules. For example, 30 minutes of activity could be accumulated throughout the day by taking the stairs in lieu of elevators or escalators, walking instead of driving short distances, using fewer labor-saving devices, and doing house or yard work (17,18, 19).
A physical activity log can be used to help individuals identify times they spend in sedentary activities for the purpose of working more physical activity into their daily routine. This offers people who dislike vigorous activity another approach to increasing their activity levels. Moreover, for people who are unable to set aside 30 minutes for physical activity, shorter episodes are clearly better than none.
Inexpensive pedometers can offer a simple way for patients to monitor their changes in activity levels. These small devices are available in most sports stores or on the Internet. Many of them can estimate distance walked or even energy expended by entering the stride length and body weight. Pedometers work best when placed firmly on the belt or waistband of a skirt. Many individuals enjoy logging the number of steps taken each day and use the device to ensure that they are indeed accumulating more activity. A value of 10,000 steps per day is gaining popularity with the media and can be traced to Japanese walking clubs (20). This may be a reasonable way for many adults to meet current physical activity guidelines, although it may not be enough for children.
The beneficial effects of moderate-intensity and/or accumulated exercise are the basis for the Surgeon General's guidelines for people who get little or no physical activity: “All children and adults should accumulate at least 30 minutes per day of moderate intensity physical activity on most, preferably all, days of the week” (1). The document Physical Activity and Public Health: A Recommendation from the Centers for Disease Control and Prevention and the American College of Sports Medicine (seehttp://www.hopkinsbayview.org/PAMreferences) promotes this approach and stresses that two other components of fitness—flexibility and muscular strength—should not be overlooked. The report advises that people who maintain or improve their strength and flexibility may be better able to perform daily activities, less likely to develop back pain, and better able to avoid disability, especially as they advance into older age.
Physical Activity and Weight Management
The prevalence of obesity has increased at an alarming rate in the United States and around the world. These increases
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are posing significant challenges to health care practitioners who take care of overweight patients. Recently, efforts have been made to quantify the role that physical inactivity may be contributing to the obesity epidemic. Although portion size and energy intake have increased over the past two decades, it appears that energy expenditure has remain unchanged or decreased slightly.
Current public health guidelines for physical activity are for 30 minutes of moderate-intensity activity each day, which offers important benefits across a broad array of health outcomes for inactive adults. These recommendations may be helpful in preventing hypertension, diabetes, and heart disease (11). It should be noted that this dose of exercise may be inadequate to thwart harmful weight gain for some persons who may need a combination of additional exercise combined with healthy eating to minimize the likelihood of further weight gain. The International Association for the Study of Obesity (IASO) reported “for the prevention of weight regain in formerly obese individuals, at least 60–90 minutes of moderate intensity physical activity or lesser amounts of vigorous activity are required.” This volume of exercise is more than the recommended amount to prevent the transition from healthy weight to overweight or obesity in the general population of 45 to 60 minutes per day (21). The IASO also suggests that obtaining the recommended levels of activity for weight control can more easily be met by helping people reduce the time spent doing sedentary behaviors by incorporating more incidental or leisure time activities into the daily routine.
Several investigators have also examined the complex relationships between physical activity levels, adiposity, and mortality (9,11,22). Blair has long argued that higher levels of fitness can counteract the elevated health risks associated with being obese (23). Several reports confirm that overweight and obese individuals who are physically active experience significant reduction in health risks compared to their sedentary counterparts (10,22,24). Although exercise by itself may not produce substantial weight loss, it is likely to result in shifts in body composition and fat distribution. In particular, several studies demonstrate that patients who participate in vigorous aerobic exercise may lose small amounts of weight on the scale but still reduce visceral fat stores. For example, we recently found that 6 months of exercise training in older men and women (55 to 75 years), which resulted in an average weight loss of only 2.2 kg, reduced total body fat by 3.5% and increased lean body mass by 3.5% (25). Importantly, exercise reduced total abdominal fat by 12%, abdominal visceral fat by 18%, and abdominal subcutaneous fat by 9%. These changes in body composition were the strongest determinants of reductions in blood pressure and improvements in risk factors associated with metabolic syndrome (7), suggesting an important pathway by which exercise improves cardiovascular health.
Resistance Exercise
Resistance exercise has long been used to enhance muscle size and strength, and its beneficial relationship to health has a strong scientific basis. In 1990, the American College of Sports Medicine added resistance training to their guidelines for exercise training in healthy adults (26). Regular resistance training can result in increased bone mineral density, lean body mass, and muscle strength (27). Moreover, it may lead to improved quality of life and promote independence in the frail elderly patient (28).
Sustained slow-movement activity, often involving small muscle groups against high resistance, is known as static activity or resistive exercise. Examples are weight lifting, pushups, sit-ups, carrying heavy packages, and handgrips. Most activities requiring lifting and straining, such as shoveling, have a large static component. In such activities there is increased peripheral vascular resistance, with subsequent increase in blood pressure but little increase in heart rate or cardiac output. Such exercises do not bring about enhancement in oxygen extraction, so they are generally not aerobic. Some aerobic-type conditioning is attained when one uses repetitive resistive exercise equipment and sequentially completes 10 to 15 repetitions on a variety of exercise machines, each designed to exercise a different group of muscles (29).
In the healthy person, gradual involvement in activities such as weight lifting may be beneficial and desirable, especially in those whose jobs require static efforts. Brief episodes of moderate resistive exercise occasionally aggravate or cause musculoskeletal symptoms but do not increase the risk of adverse cardiovascular effects. In 2000, the American Heart Association issued a scientific advisory on resistance exercise in individuals with and without cardiovascular disease (see http://www.hopkinsbayview.org/PAMreferences). These guidelines note that after careful screening and risk stratification, and when appropriately prescribed, resistance training is an effective method for improving muscular strength and endurance, preventing and managing a variety of chronic medical conditions, modifying cardiac risk factors, and enhancing psychosocial well-being. It is suggested, however, that a resistance training program should complement, rather than replace, an individual's aerobic exercise regime.
Resistance training may be especially beneficial in preserving health and quality of life as people age. Muscle dysfunction and atrophy, common among the elderly, increase the risk of falls (a major cause of mortality), bone fractures, and functional dependency. For example, low dynamic quadriceps strength is associated with difficulties in standing from a seated position and decreased distance covered during a 6-minute walk test (30). A number of studies have confirmed the benefits of resistance training in older subjects. An 8-week high-intensity resistance training program increased muscle strength and mass and
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functional mobility among frail nursing homes residents who were on average 90 years of age (28). Other studies have shown that strength gains in the elderly are associated with significant increases in gait speed, improved ability to rise from chairs, better balance, and less reliance on canes to assist in walking (28,31,32). All of these beneficial changes lead to a reduced risk of falls (33).
Getting Patients Moving
Clinician's Role
Helping patients to change modifiable risk factors is a difficult but important challenge for health care professionals (see Chapter 4). It is noteworthy that despite a barrage of media-delivered health messages, fully 80% of Americans cite their physician as the primary source of health information (34). With the average adult patient making more than two medical visits per year to their primary care practitioner, there are multiple opportunities to intervene (35). Although clinicians generally believe that most patients should exercise, many who do counsel their patients about health-habit modifications tend to address smoking and weight problems more frequently than they address a sedentary lifestyle (4,34). Patients may interpret a lack of advice to become more active as a message that physical activity is not important. Tailoring messages to meet patients’ needs in primary care settings has been found to improve dietary behaviors (36), smoking cessation outcomes (37,38), and activity levels in sedentary patients (39). Many health care practitioners, however, do not feel adequately prepared in the detail of tailoring an exercise prescription for their patients (40).
Prescribing Exercise
A systematic approach to prescribing exercise is essential if one's effort is to be successful.
Exercise/Activity History
To help a patient adopt a more active lifestyle, it is critical to listen carefully to the patient's description of what barriers exist to increasing their physical activity level and then to build on the patient's preferences. To illustrate how these principles can be applied, consider the following case.
Joe is a 51-year-old male who is basically healthy. He works at an office job and was successful in quitting smoking (30 pack-years) but has gained 10 kg since. He comes for a checkup. Aside from the usual evaluation, the following series of questions and recommendations should be considered:
Specifics of an Exercise Prescription
Setting small goals for a patient to achieve between office visits is the best way to start. For example, after establishing baseline levels of physical activity, a first step for a sedentary person could be to prescribe increased lifestyle activities. The prescription should be very specific, achievable, and realistic. Writing the recommendation on a prescription pad may increase the likelihood of the activity being followed (Fig. 16.1). Table 16.4 lists information useful for planning and writing down exercise prescriptions according to a person's baseline activity profile.
A sequential approach to assessing and recommending physical activity is presented in the flow diagram in Fig. 16.2. Each patient will fit one of three profiles: adequately active, inadequately active, or sedentary. The first step involves assessing current activity levels. For sedentary patients, an exercise history should explore potential strategies to initiate activity as well as the willingness to augment levels of activity. During followup visits, exercise
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participation should routinely be readdressed, commended, and/or encouraged anew.
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FIGURE 16.1. Simple written exercise prescription with specific achievable lifestyle activity goals. |
Exercise Adherence
Despite the best intentions, half of all adults who begin or renew an exercise program will fail to maintain it at the level they intended (42). In a typical supervised setting, approximately 50% of the clients will drop out within 6 months to a year (43). Thus, the focus of an exercise or activity program should be to decrease sedentary living and to focus on long-term adherence to the program.
Table 16.5 lists barriers and predictors of regular exercise adherence. A sincere recommendation from one's primary care practitioner to begin an activity program may be one of the strongest predictors of long-term exercise (44). During subsequent office visits, showing interest in and encouraging the patient's physical activity can be very helpful in increasing adherence. Even small steps in the right direction are helpful and worthy of approval.
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TABLE 16.4 Exercise Prescription Principles for the Apparently Healthy Adult Based on Current Levels of Physical Activity |
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FIGURE 16.2. A framework for physicians to initiate discussion about exercise and physical activity. (From Christmas C, Andersen RE. Exercise and older patients: guidelines for the clinician. J Am Geriatr Soc 2000;48:318 , with permission.) |
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TABLE 16.5 Barriers to and Predictors of Exercise Adherence |
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It is also important to capitalize on the fact that persons who are aware of the health benefits of exercise are more likely to become regular exercisers (45). Printed materials and lists of suggested reading can help the patient to self-educate and may also enhance adherence (Table 16.2).
A lack of time is one of the most common reasons cited by adults for not exercising. Let patients know that three programmed workouts per week for a minimum of 20 minutes is optimal but that doing something is much better than no activity at all because the greatest gains to health, as described earlier, are derived by moving from being totally sedentary to a moderate level of fitness. In many cases, patients are able to find more time for exercising once they become active and notice results from the program.
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Periodic feedback on health improvements related to lifestyle improvement can lead to renewed enthusiasm. Recording prescribed physical activity in patient charts can help with followup office visits and exercise-related discussions. Office-based measurements that can be used as measures of success are reductions in resting heart rate, blood pressure, and body mass index and an improved lipid profile. At home, the individual should be encouraged to monitor their exercise performance (i.e., time to walk a mile, number of steps per day) body weight, and perhaps more important, their waist circumference.
Choosing the intensity level is important. Sedentary persons who begin exercising at moderate intensities are more likely to adhere to their programs than those who begin vigorously. Excessive frequencies (e.g., more than 5 days per week) or intensities that the patient perceives as being “hard” may also lead to higher dropout rates (43,45). The Borg Rating of Perceived Exertion scale can be used to help patients understand and select the appropriate exercise intensities (46).
To reduce the risk of injury, progression should be moderate as well, because sedentary patients who are unaccustomed to regular activity are at greater risk of an overuse injury from starting out too vigorously. Exercise-related injuries predictably increase the risk of dropping out of exercise programs. A 5% per week increase in the duration or intensity of training sessions will help to reduce the risk of injury. Individuals who use exercise equipment should also be encouraged to learn how to adjust the equipment to minimize injury risk. For example, a bicycle seat that is set too low may result in knee pain. Patients should consider a trial membership at a health club before joining or as a way of trying equipment before making a purchase for home use.
Appropriate footwear is important for all individuals who exercise, but even more so for those who are overweight or who suffer from joint or bone problems. High-quality shoes can dramatically reduce the risk of overuse injuries. Selecting appropriate footwear can be somewhat daunting for many beginning exercisers because there are hundreds of shoes to pick from. Encouraging patients to purchase their shoes from a vendor that specializes in athletic footwear will ensure that they receive a “sport-specific” shoe that is properly fitted. Those patients with known foot problems should seek advice from a podiatrist. Popular running magazines and fitness magazines publish annual ranking of the top footwear for each type of shoe on the market. For persons whose main activity will be walking, the features of appropriate shoes are illustrated in Chapter 73.
Patients who choose walking or jogging as a mode of activity should be encouraged to exercise on appropriate terrain. Hard surfaces should be avoided whenever possible. For example, walking or running on concrete walks can cause ankle, knee, and hip injuries. Uneven or canted surfaces (e.g., beaches or crowned roads) may result in knee problems. Cross-training or performing different types of activity may help to reduce risk of injury and boredom.
Long-term exercise adherence is enhanced by support from spouses, friends, exercise leaders, and family (42,43,47). Health care practitioners can become a vital link in their patient's social support network, even if contact is infrequent.
Specific References*
For annotated General References and resources related to this chapter, visit http://www.hopkinsbayview.org/PAMreferences.
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