Exercise as a Treatment for the Risk of Cardiovascular Disease
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- Aijaz, B., Brown, T.M., Sanderson, B.K. et al. Curr Treat Options Cardio Med (2010) 12: 329. doi:10.1007/s11936-010-0078-5
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Regular physical activity decreases the risk of cardiovascular disease and modifies multiple cardiovascular risk factors. The optimum amount of exercise continues to generate debate; however, the general recommendation is that all adults should engage in 30 min of moderate-intensity physical activity on five, and preferably all, days of the week. Despite extensive data and recommendations, a significant proportion of the US adult population remains sedentary. Promoting physical activity at a public level remains a major challenge because of the presence of multiple behavioral, physical, and environmental barriers. Health care providers have an opportunity and a responsibility to include exercise counseling in routine office visits.
References have long been made to the beneficial effects of exercise on health; Hippocrates noted “Walking is man’s best medicine.” During the past century, scientific evidence emerged regarding the multitude of cardiovascular health benefits to adults conferred by physical activity and its resultant cardiorespiratory fitness (CRF) . Robust data from several lines of investigation exist to support this conclusion [2–5]. Detailed guidelines by various professional societies outline the benefits of exercise [6, 7••, 8••]. Yet, more than half of US adults do not exercise regularly [8••], and one quarter report no leisure-time physical activity . National data demonstrate that 73% of US women and 66% of men fail to meet the minimum 30-minute daily activity guideline, and 41% of women and 35% of men do not engage in any leisure-time physical activity at all . A recent update from the American Heart Association states that only 34% of US adults reported regular leisure-time physical activity; this number was considerably lower in minorities . The health consequences of a largely sedentary US population pose a significant challenge. The reasons, both perceived and real, for not adopting a physically active lifestyle are numerous. Additionally, the ongoing debate regarding the “correct dose” of exercise among various organizations has made it difficult to follow recommendations for optimal physical activity [7••, 8••, 12, 13].
In this article, we review the long-term cardiovascular benefits of exercise, with specific emphasis on the optimal level of exercise recommended for primary prevention of cardiovascular disease (CVD) that is supported by current data.
Physical activity, exercise, and CRF
Physical activity is a behavior generally measured by self-reported level of activity and occasionally by activity monitors. The 1996 National Institutes of Health Consensus Conference Statement on physical activity and cardiovascular health defined physical activity as “bodily movement produced by skeletal muscle that requires energy expenditure and promotes health benefits” . CRF is a physiologic characteristic measured objectively by exercise testing [7••]. However, it is directly influenced by, and correlates with, regular physical activity . Exercise is physical activity structured and planned with the goal of improving one’s health or fitness. Therefore, not all physical activity is exercise. Physical activity and exercise are important health promotion topics at the population level, but it also is necessary for providers to integrate exercise counseling into routine office visits and be familiar with assessing CRF to help guide appropriate exercise recommendations.
Effect of exercise on CVD risk factors
Physical inactivity is a major risk factor for CVD. Even after adjustment for traditional risk factors, physical inactivity is responsible for 12.2% of the global burden of myocardial infarction . Regular physical activity has a favorable effect on multiple CVD risk factors . Although an inverse association exists between various CVD risk factors and exercise, the benefits of exercise have been shown to exist independent of improvements in these risk factors. It also is important to note that many benefits of regular exercise go beyond the cardiovascular system, with effects on the musculoskeletal system, cognition, psychological health, and some cancers.
Moderate-intensity exercise over the long term decreases both systolic and diastolic blood pressure as the result of a combination of effects on the autonomic nervous system, conditioning the heart and vascular system . These effects are seen in both normotensive and hypertensive individuals and are independent of weight loss associated with regular physical activity .
Exercise has favorable effects on blood lipids, with a moderate decrease in triglycerides (20–24%) and low-density lipoprotein (LDL) cholesterol (8–20%) and a rise in high-density lipoprotein cholesterol (3–12%). This impact is most notable when regular physical activity is combined with dietary modifications . Physical activity also has been shown to reduce the concentration of small, highly atherogenic LDL particles, resulting in a relative increase in the concentration of large, less atherogenic LDL particles .
Insulin resistance and diabetes
Exercise results in a decrease in insulin secretion, lower fasting insulin levels, decreased insulin resistance, and increased insulin sensitivity. In observational studies and interventional trials, physical activity has been shown to be associated with a reduced incidence of diabetes [22, 23]. The American Diabetes Association supports other national recommendations for 30 min of physical activity daily for the prevention of diabetes .
Regular physical activity, particularly aerobic exercise, modifies obesity through multiple mechanisms. Exercise results in favorable changes in body fat distribution and decreases in overall fat mass. It is important to note that the current obesity epidemic is driven by both excess calorie intake and a sedentary lifestyle. Understandably, in studies in which exercise was the sole intervention for weight loss, only modest results were seen . However, when calorie reduction was combined with regular aerobic exercise, weight loss was not only greater but also more sustainable. Pursuing intensive exercise for weight loss may not be practical or safe in most patients. For individuals seeking weight loss through exercise, the independent benefits of regular physical activity also should be outlined. Moreover, with aerobic exercise, favorable fat redistribution may occur without apparent changes in body mass index or weight, which often is the sole focus for many individuals. A high level of physical activity modifies obesity-related mortality risk [25, 26].
Physical activity guidelines supported by professional societies
For overall health
US Department of Health and Human Services
150 min/wk of moderate-intensity or 75 min/wk of vigorous-intensity aerobic physical activity, or an equivalent combination, in episodes of at least 10 min
Centers for Disease Control and Prevention
The President’s Council on Physical Fitness and Sports
Muscle-strengthening activities involving all major muscle groups on ≥2 d/wk
NIH and NHLBI
American College of Sports Medicine
Moderate-intensity aerobic physical activity for a minimum of 30 min 5 d/wk or vigorous-intensity aerobic physical activity for a minimum of 20 min 3 d/wk in bouts of ≥10 min
American Heart Association
Additional benefit of exceeding the minimum recommended amounts of physical activity
For weight maintenance
American College of Sports Medicine
Moderate-intensity physical activity 150–250 min/wk to prevent weight gain; greater amounts of physical activity (>250 min/wk) to achieve significant weight loss
American Dietetic Association
US Department of Health and Human Services
60 min of moderate- to vigorous-intensity activity on most days of the week to help prevent gradual weight gain; at least 60–90 min of daily physical activity to sustain weight loss
Department of Agriculture (Dietary Guidelines for Americans)
Institute of Medicine
Average of 60 min/d of moderate-intensity physical activity or shorter periods of more vigorous exertion to maintain a normal body mass index; no recommendations for weight loss
International Association for the Study of Obesity Consensus Statement
Moderate-intensity activity of 45–60 min/d to maintain weight and 60–90 min of moderate-intensity activity (or lesser amounts of vigorous-intensity activity) for weight loss and prevention of weight regain in previously obese individuals
Inflammation plays a central role in the development of CVD. The levels of various inflammatory markers have consistently been reported to be elevated in patients with atherosclerosis and CVD. An inverse dose–response relationship has been observed between physical activity and inflammatory markers including C-reactive protein, interleukin-6, and white blood cell count .
Hemostasis and thrombotic function
Exercise improves endothelial function and increases vessel reactivity. It increases nitrous oxide and prostacyclin availability, thereby improving endothelial-dependant vasodilation . Brachial artery reactivity was notably improved in patients engaged in 15–30 min of walking on a treadmill three times weekly .
Mechanisms for the protective effects of exercise on the cardiovascular system
Physical activity improves cardiovascular health through multiple and complex interactions, all of which are not completely understood. Regular physical activity increases myocardial oxygen supply and improves myocardial contraction and electrical stability . Exercise also increases coronary collateral circulation and myocardial capillary density. The central role of insulin resistance as a mediator for CVD has been investigated extensively. Increased insulin sensitivity occurs with physical activity , which may be one of the important mechanisms by which exercise reduces the risk of CVD. Exercise also has favorable hemostatic mechanisms by which it decreases platelet aggregation and increases fibrinolytic activity . It has been associated with lower concentrations of inflammatory markers, stabilization of atheromatous plaques, and improvements in endothelial function. Exercise increases vagal tone and decreases sympathetic nervous system activity and heart rate, which all have been associated with decreased mortality .
Dose of exercise
The beneficial role of exercise in preventing CVD is indisputable; however, the correct “dose” of exercise, which is a function of type, duration, and intensity of exercise, continues to generate debate. General agreement exists that there is a linear dose–response relationship between physical activity and reductions in CVD risk, at least up to a certain level of activity [8••, 36, 37]. The upper limit of exercise above which no additional health benefits are seen is not clear at present and may well vary by gender, age, and other characteristics. A challenge to recommending an optimum dose of exercise has been that much of the physical activity data are collected through self-reported methods that are highly subjective , despite attempts to standardize energy expenditure from different exercises . The optimum exercise dose also depends on the desired outcome; for instance, the recommendations to achieve weight loss are different from those meant to decrease cardiovascular risk (Table 1). Exercise recommendations may need to be tailored to an individual’s current level of physical activity and CRF, clinical and risk factor status, and psychological readiness to make behavior changes.
Type of exercise
Questions regarding which type of exercise (aerobic, endurance, resistance training, and leisure-time activity) confers maximal benefit frequently come up in clinical practice. Recommendations support a variety of exercises to improve the components of physical fitness, including aerobic, muscular strength, endurance, flexibility, and body composition exercises . Additionally, specific exercises to improve balance and agility are needed for older or extremely deconditioned adults . The intensity of exercise is related mostly to aerobic exercise, and in general, guidelines support moderate-intensity “aerobic” physical activity [8••]. In an elegant analysis by Tanasescu et al. , increased total activity was associated with a decreased risk of CVD in a dose-dependent manner after adjustment for traditional CVD risk factors. However, high-intensity exercises such as rowing, running, and weight training were associated with greater CVD risk reduction. Data support that resistance training should be part of a regular exercise program . Muscle-strengthening activities lead to increased bone strength, muscular fitness, and mass. Examples of muscle-strengthening exercise include resistance training, resistance bands, and using body weight for resistance, as in pull-ups, sit-ups, and push-ups. Resistance training is recommended for older individuals and patients with CVD. However, given its effect on body composition and resting metabolic rate, the recommendations may be extended to all adults [32, 43]. Current guidelines recommend resistance training to improve muscle strength and endurance for a minimum of two nonconsecutive days each week in addition to aerobic activity [8••]. This training may include eight to 12 repetitions of eight to ten exercises of large muscle groups including the chest, back, abdomen, shoulders, legs, and hips. Flexibility also is an important part of physical fitness, and stretching exercises should be part of an exercise regimen, although at present their impact on overall health is unclear. It is important to note that the time spent on stretching and muscle-strengthening activities does not count toward the overall minimum aerobic exercise goal.
Duration of exercise
A common question that comes up in clinical practice is whether splitting the recommended duration of exercise into multiple, shorter sessions leads to benefits similar to those of a single, longer session (≥30 min). In a study of middle-aged men, Lee et al.  showed that the accumulation of shorter sessions of physical activity compared with a longer, continuous session of exercise did not show any significant difference in terms of CVD risk reduction when total energy expenditure was taken into account. DeBusk et al.  reported that 30 min of exercise per day for 8 weeks led to improvement in physical fitness regardless of the duration of activity (in this study, bouts of at least 10 min were compared with longer ones).
For persons who currently are sedentary, a reasonable recommendation is to allow accumulation of short sessions of physical activity. The current guidelines endorse breaking the daily goal of 30 min of activity into bouts no shorter than 10 min. What about the situation in which patients mention that their “adequate walking” at work constitutes daily exercise and consider themselves physically active? First, the clinician should acknowledge that some physical activity is better than none but stress that “intentional” or purposeful structured exercise in addition to routine physical activity is important. Second, whether activities of daily living lasting less than 10 min, such as walking around at work and home or walking while shopping, confer any health benefit is unknown, and importantly, they currently are not recommended as a substitute for more organized and sustained exercise sessions [8••]. Physical activity above the minimum recommended amount likely provides greater health benefits, but the emphasis should be to encourage a regular exercise program that can be maintained over time to achieve longer-term benefits. The point of maximum benefit, which likely varies among individuals, also is unclear. Establishing the maximum amount of exercise known to decrease cardiovascular risk is not too relevant when encouraging sedentary persons to initiate exercise.
Frequency of exercise
Whether the frequency of exercise, the total time spent exercising, and the energy expended equally predict CVD risk is debatable. Mensink et al.  showed that frequency of exercise was more strongly associated with coronary risk factors, including serum lipids, blood pressure, and body mass index, than exercise intensity or total time spent exercising; however, the results of other studies were conflicting. Current guidelines recommend aerobic activity at least 5 and preferably all days of the week. Vigorous exercise for a minimum of 3 days per week also provides health benefits and may be substituted for or combined with moderate-intensity exercise. Whether the benefits of exercise exist for more infrequent exercise is not known. A minimum of 3 days per week of exercise is in addition to any light-intensity routine activity of daily living.
The frequency of exercise represents the adoption of a healthy lifestyle in general and therefore remains the most challenging aspect of adopting “regular” physical activity. Persons exercising daily have made physical activity part of their everyday lives.
Intensity of exercise
- Discussion continues as to whether low-, moderate-, or high-intensity exercise is beneficial for preventing CVD [32, 36]. Challenges in determining the intensity of exercise are imprecise measurement and inherent errors in self-reporting of physical activity. “Moderate-intensity” aerobic activity (at least brisk walking) noticeably accelerates the heart rate (Table 2) [8••]. Moderate levels of exercise can be achieved by brisk walking, cycling, swimming, yard work, and mowing the lawn . Vigorous-intensity activity results in rapid breathing and a substantial increase in heart rate [8••]. The intensity of exercise also can be determined by the amount of energy expended per minute of activity relative to rest or metabolic equivalents (METs). One MET equals the resting metabolic rate of approximately 3.5 mL/kg/min of O2. Moderate-intensity activities expend 3.0 to 5.9 times, and intense exercise expends 6 or more times, the energy expended at rest [7••]. The relative energy intensity also depends on the fitness level of the person, with more fit persons perceiving less energy intensity for any given level of activity [7••]. Numerous studies favoring vigorous exercise to reduce CVD risk exist [48–50]. Other studies have suggested that vigorous exercise does not provide additional risk reduction beyond moderate ranges of total physical activity [51, 52]. Sesso et al. , using the Harvard alumni health study, reported that engaging in a moderate amount of physical activity (>4,200 kJ/wk) led to approximately a 20% reduction in CVD risk. Tanasescu et al  showed that exercise intensity provided additional risk reduction beyond the total amount of physical activity. Leisurely walking (<2 mph) has not been consistently reported to reduce CVD risk significantly, whereas brisk or pace walking can increase CRF and decrease CVD risk. Similarly, light-intensity daily activities such as cooking, self-care, casual walking, and shopping should not count toward recommended daily exercise [8••]. A recent meta-analysis of 22 prospective studies including 510,000 healthy individuals showed that persons in both the high and moderate category of leisure-time physical activity had a significantly reduced risk of CVD compared with those in the sedentary category (RR, 0.73; 95% CI, 0.66–0.80; P < 0.001 and RR, 0.88; 95% CI, 0.83–0.93; P < 0.001) .Table 2
Examples of activities based on intensity (metabolic equivalent level)
Moderate intensity (3.0–6.0 METs)
Brisk walking (3–4 mph but <4.5 mph)
Heavy household activities such as sweeping floors, washing windows, washing car, carrying wood, mowing lawn with push mower
Bicycling (<10 mph)
Tennis (doubles), badminton (doubles), basketball (shooting), golf (walking, pulling clubs), table tennis, leisurely swimming, sailing boat, windsurfing
Vigorous intensity (>6.0 METs)
Walking at a very brisk pace (>4.5 mph), jogging, or running
Hiking uphill at moderate pace with a light backpack
Shoveling snow or coal, digging
Carrying heavy loads of wood, bricks, etc.
Heavy farming, such as bailing hay
Swimming, tennis (singles), soccer, hockey, basketball (game), volleyball, cross-country skiing, jumping rope
Bicycling (>10 mph)
A balanced and practical approach is to combine moderate and vigorous activity to attain health benefits, as suggested in recent guidelines from the American College of Sports Medicine [8••]. For individuals just initiating exercise, it is wiser to choose low- to moderate-intensity exercise and gradually build up to include more moderate- to vigorous-intensity exercises.
Initiating physical activity
Low-risk and asymptomatic men and women who plan to undertake moderate-intensity physical activity at the minimum recommended levels do not need to consult a physician or undergo exercise stress testing, as the rate of cardiovascular complications is extremely low [40, 54]. For sedentary individuals, using common sense with gradual initiation of activity, with bouts of 5–10 min at low intensity and building up over several weeks to months, will prevent injuries and avoid any increased cardiovascular risk. For individuals who are completely sedentary, incorporating any amount of exercise in their daily lives is better than not exercising at all. Initiation of some physical activity is likely to gradually result in regular exercise. Symptomatic persons or those with active chronic diseases should consult a physician before initiation of moderate or intense physical activity .
Risk of physical activity
A question that comes up during patient counseling is whether there is any harm from physical activity or an increased risk of death in physically active individuals. Before intense exercise is undertaken, proper training and conditioning are essential to prevent injury. The incidence of overall injuries associated with leisure-time physical activity was similar in active and inactive persons in a survey involving 1,000 participants . Similarly, sedentary individuals should gradually build up the amount and intensity of exercise to a target of at least 30 min of aerobic exercise. The risk of sudden cardiac death is not increased with moderate-intensity exercise. During intense exercise, a slightly increased risk of sudden cardiac death has been reported, but the data are conflicting . This risk is minimal compared with the 25% to 50% increased risk of developing CVD and its associated morbidity and mortality in sedentary individuals [7••, 8••].
How long does it take before beneficial effects of exercise are seen?
How long does it take before beneficial effects of exercise are seen? The answer to this question depends on the individual’s health status, his or her current activity level, and the specific benefits desired. The benefits of exercise are both acute and long term. Improved cardiovascular fitness, muscle strength, and effects on blood pressure and mood may be seen only after a few weeks, whereas it may require months to years of being regularly physically active to reduce the risk of chronic diseases. Therefore, current recommendations support being physically active for life [7••]. It is possible that the beneficial effects of exercise may decrease and eventually be nullified if one stops exercising.
Counseling on physical activity
To deal with the current physical inactivity epidemic, a broad approach is needed within clinical practice. All physicians should encourage their patients to engage in regular physical activity . For exercise counseling of physically inactive individuals, physicians should first assess their readiness to change. This assessment may be based on the five stages suggested by the transtheoretical model of behavior change: precontemplation, contemplation, preparation, action, and maintenance. Importantly, exercise prescription at the first encounter with a patient in the precontemplation stage likely will not produce the desired results. This model has been applied successfully to smoking cessation. For each stage, physicians can assess the individual’s current level of physical activity, barriers to being physically active, and current level of education, then appropriately intervene by providing assistance, information, and skills to help the patient change his or her behavior [57, 58•]. Additional resources, such as an exercise physiologist, an exercise rehabilitation program, or a health educator should be used whenever available. Instructions regarding physical activity should be clear, preferably via a formal exercise prescription. Prescription of exercise should include the mode of exercise (eg, walking, elliptical, rowing, cycling, swimming, recumbent machines) and the intensity, duration, and frequency of exercise. Although target heart rate has been used in exercise programs for secondary prevention, moderate-intensity exercise may be recommended when the results of exercise testing are not available. Moderate-level exercise generally is achieved when an individual can speak during exercise but prefers not to or rates his or her level of exertion between 5 and 7 on a perceived exertion scale of 0 to 10 [59••]. See Table 2 for examples of moderate- and vigorous-intensity activities. Follow-up visits are essential to review and reinforce change. For additional information, readers are advised to review the detailed recommendations by the US Department of Health and Human Services (http://www.health.gov/paguidelines/), the Surgeon General’s report on physical activity (http://www.cdc.gov/nccdphp/sgr/index.htm), and “Exercise Is Medicine,” which is endorsed by the American College of Sports Medicine and has several physician tools to facilitate counseling (http://exerciseismedicine.org/physicians.htm).
Exercise is essentially a polypill with potent therapeutic effects on an individual’s cardiovascular health. It is a low-cost, highly efficacious intervention to decrease the global risk of CVD. To quote Dr. William Roberts , exercise is “an agent with lipid-lowering, antihypertensive, positive inotropic, negative chronotropic, vasodilating, diuretic, anorexigenic, weight-reducing, cathartic, hypoglycemic, tranquilizing, hypnotic and antidepressive qualities.” Although the optimum amount and type of exercise may not be determined in the near future, the old adage “everything in moderation” holds true for exercise as well. A moderate level of physical activity is a target well within the reach of most of the US adult population. However, multiple social, personal, environmental, and psychological challenges exist in adopting regular physical activity. As researchers work to completely understand the key physiologic role exercise has in CVD risk factors, it is critically important to identify strategies to increase levels of sustained physical activity among the population.
No potential conflicts of interest relevant to this article were reported.