Exercise for Prevention of Chronic Diseases

Question: Intuitively, being physically active is good for health. What are the benefits of physical activity and exercise on decreasing the risk of developing chronic diseases such as heart disease? What level of activity is needed for there to be benefits?

A Evidence continues to accumulate on the wide-ranging health and fitness benefits of physical activity and exercise. The second edition of the Physical Activity Guidelines for Americans (PAGA) begins with the following statement that underscores the power of choosing to be active: “Being physically active is one of the most important actions that people of all ages can take to improve their health” (¹). Health promotion and disease prevention are two sides of the coin when it comes to physical activity and exercise; the dual benefits are an inspiration for everyone to seek ways to make movement part of daily routines.

Over the years, researchers have explored the potential effect of physical activity and exercise. The list of health benefits continues to grow as evidenced by Box 1 taken from the 2018 PAGA (¹). Benefits are available for all ages and both males and females. For health and fitness professionals, review this as more than just a list; consider the influence that fully realizing the benefits outlined can have on individuals, families, and communities.

Although the list of benefits continues to grow, translating recommendations into action continues to be a challenge. Adherence to the recommended levels of aerobic activity as outlined in the 2008 PAGA is relatively unchanged for adults, as noted in a study examining activity levels from 2007 to 2016 (²). Even when considering work-related and transportation-related aerobic activity in addition to leisure-time activity, adherence is only around 65% (previous studies looking at just leisure-time activity are under 50%) (²). Unfortunately, during this same time period, sedentary behavior time increased to nearly 6.5 hours per day (²). In a recent report by the U.S. Centers for Disease Control and Prevention (CDC), the prevalence of U.S. adults who met both aerobic and muscle-strengthening activity guidelines has improved (2008 to 2017), but prevalence is still very low (increase from 18.2% to 24.3%) (³). See Figure 1 for an infographic from the CDC displaying this data.

Figure 1: Physical activity adherence in U.S. adults infographic (³).

Given that too few Americans are meeting the recommended levels of aerobic and strengthening exercise, the opportunity for improvement is tremendous (see the Wouldn’t You Like to Know article “Physical Activity Guidelines for Americans: The Relationship between Physical Activity and Health” for specifics on targeted levels of activity and background on the PAGA [⁴]). Getting people to start moving is key, as shown in Figure 2. This figure displays the relationship between physical activity and mortality (¹). All-cause mortality refers to death from any cause, including heart disease, cancers, and other causes. Shifting from no activity to even around 3 MET-hours per week lowers the hazard ratio, as shown in the figure (for more on hazard ratios, see Box 2; for information on MET-hours per week, see Box 3). Although 150 to 300 minutes of moderate physical activity is a meaningful target in PAGA, the figure shows “a large benefit occurs when a person moves from being inactive to being insufficiently active” (¹). The value of going from being sedentary to even some movement is clear, with additional benefits as a physical activity program is progressed. Also of note for individuals who engage in more than the minimum recommended levels of exercise, the hazard ratio does not increase with higher levels of activity (i.e., there is not an increase in risk) (¹).

Figure 2: Relationship of moderate-to-vigorous physical activity to all-cause mortality (¹).

Researchers have examined the effect of activity in a number of studies. For a recent example, in a population-based cohort study in the United Kingdom (i.e., in a cohort study a group is defined and followed over time), those who were active at the start and had maintained activity levels had lower all-cause mortality risks (28% for medium level baseline activity and 33% for high baseline physical activity) (⁵). Of note, there were benefits for increasing physical activity, no matter the baseline level—even for those in the lowest activity level group. Lower mortality was found from all causes, cardiovascular disease, and cancer even when other lifestyle factors such as diet, body mass index, blood pressure, triglycerides, cholesterol, and medical history were considered (⁵). The researchers concluded “meeting and maintaining at least the minimum physical activity recommendations would potentially prevent 46% of deaths associated with physical inactivity” (⁵).

The effect of fitness is another area of research interest. Estimated cardiorespiratory fitness (eCRF) has been found to be associated with a lower risk of having a first myocardial infarction (⁶). In this study, eCRF was determined based on sex-specific models incorporating age, waist circumference, resting heart rate (HR), and leisure-time physical activity. The use of an estimation, rather than direct measure, of cardiorespiratory fitness was suggested to be of practical value in clinical settings where routine measurement of fitness is not common (⁶). In a study using submaximal treadmill exercise tests for apparently healthy adults, predicted peak oxygen consumption and postexercise HR recovery were predictors of both short-term and long-term cardiovascular disease risk (⁸). Measured peak oxygen consumption was examined at two time points in another study (⁹). The change in cardiorespiratory fitness over time was determined to be a strong predictor of mortality (all-cause, cardiovascular disease, and cancer) (⁹). Risk for all-cause mortality was 37.8% lower for each MET increase in fitness (⁹). Measured oxygen consumption was noted as a strength of the study as estimation errors are avoided by using direct measurement of cardiorespiratory fitness (⁹). Considering the value in predicting mortality and in classifying risk, cardiorespiratory fitness is proposed as an important clinical vital sign (¹⁰).

Researchers also continue to explore mechanisms behind the benefits of exercise on cardiovascular disease. Changes in lipoproteins with exercise training (e.g., increase in the size of LDL and HDL particles and a decrease in VLDL particle size) may be involved in providing lower risk for cardiovascular disease (¹¹). Exercise may affect the arterial walls to interfere with the development of atherosclerosis and improves insulin sensitivity (¹¹). Oxygen delivery is improved with exercise thanks to the dilation of vessels; oxygen uptake and use at the cellular level increases as the function of mitochondria in cells is enhanced (¹²). Blood pressure increases during exercise, but the long-term beneficial decrease in blood pressure is likely due to a reduction in resistance to blood flow promoted by vasodilation of vessels brought on by the release of nitric oxide and prostacyclin (helping to relax the smooth muscle of vessel) (¹¹). Other mechanisms of interest include how exercise changes inflammation (i.e., effects on immune cells), affects the gut, and interacts with nutrition (¹¹). Exercise provides a bodywide challenge to cells, tissues, organs, and systems; further research into the interactions and adaptations resulting from exercise will help to improve risk reduction (¹²).

Even as aspects on how exercise promotes positive changes continue to be explored, recommendations on the amount and type of activity are widely supported. The PAGA recommendations are reflected in the first column of Figure 1, focusing on aerobic and muscle-strengthening activities. The 2019 American College of Cardiology and American Heart Association’s (ACC/AHA) Guideline on the Primary Prevention of Cardiovascular Disease recommends adults be counseled during health care visits to “optimize a physically active lifestyle” (¹³). Recommendations noted to reduce atherosclerotic cardiovascular disease risk mirror the aerobic activity recommendations of the PAGA (¹) and the American College of Sports Medicine (ACSM) (¹⁴), including that adults “engage in at least 150 minutes per week of accumulated moderate-intensity or 75 minutes per week of vigorous-intensity aerobic activity (or an equivalent combination of moderate and vigorous activity)”; that adults unable to meet this level of activity engage in “some moderate- or vigorous-intensity physical activity, even if less than this recommended amount”; and that adults decrease daily sedentary time. Note that this recommendation to decrease sedentary time is presented as having potential but reflects a “weak” level of evidence. This simply means that although there is an association between sedentary behavior and cardiometabolic risk, limited research is currently available related to the limits and best methods to reduce/modify sedentary behavior. (For more information on decreasing sedentary behavior, see the Wouldn’t You Like to Know article, “Sitting Less, Moving More” [¹⁵]).

The ACC/AHA recommendations focus on aerobic activity (¹²). In addition to aerobic activity, muscle-strengthening activities are recommended within the PAGA and by ACSM; stretching exercises to increase flexibility also are encouraged, although time in flexibility-related activities does not count toward either the aerobic or the muscle-strengthening guidelines (^1,14). The health benefits of flexibility exercises are not known, although such activities allow for increased ease of movement in activities requiring more flexibility (¹). Balance training (¹) and neuromotor exercise training (¹⁴) are additional aspects to consider within an exercise program. For examples of how the various components could be combined in an exercise program, see the beginner program shown in Table 1 and an intermediate program in Table 2.

TABLE 1: Sample Beginner Exercise Program for Adults

TABLE 2: Sample Intermediate-Level Exercise Program for Adults

Although the scientific support for the value of an active lifestyle continues to grow, adherence is lacking. Is this due to lack of motivation, environmental factors, or simply not enjoying activity? As individuals seek to increase activity, these and many other factors may interact to determine their ability to succeed. Listed below are some techniques that might be helpful in developing the habit of activity (¹⁶):

• Focus on small quantities of physical activity

Because targets may be seen as unattainable (e.g., 150 minutes of aerobic activity weekly for someone currently inactive), appreciating the value of any activity may help to remove barriers to getting started and then increasing activity over time.

• Increase self-regulation

Self-management helps to promote behavior change, including self-monitoring (e.g., activity trackers), goal setting, and feedback (e.g., comparing activity over time).

• Develop habits

A habit is an “automatic sequence of actions in response to particular cues.” Formation of habits can be helpful in increasing activity (e.g., parking farther from the destination in order to incorporate more walking time). A duration of around 6 weeks has been found to allow establishment of physical activity habits.

• Increase access

Environmental factors can help people engage in activity. For example, access to fitness facilities and proximity to parks or walking paths.

In addition, being part of a group, whether led by health and fitness professionals or within a peer-group, can be useful as individuals navigate personal decisions (¹). Support from others can help when getting started, as well as when maintaining one’s exercise program or when seeking to resume after a lapse. For more resources on encouraging activity, see chapter 8 in the PAGA: “Taking Action: Increasing Physical Activity Levels of Americans” (¹).

CONCLUSION

Lifespan simply reflects the number of years of life, whereas healthspan is a term used to describe “the number of years an individual is healthy and free from debilitating disease” (¹⁷). Physical activity is one of many aspects that contribute to prolonging one’s healthspan, as well as the lifespan. Health and fitness professionals are key in promoting the message that “…some activity is better than none…” (¹⁴). Lowering risk for chronic disease while realizing improvements in fitness starts with the first steps—moving from sedentary behavior to some activity, and then from some activity toward recommended levels. Translating knowledge into action is not simple, but the rewards are well worth the effort.

Box 1. Health benefits associated with regular physical activity (¹)

Children and Adolescents

• Improved bone health (ages 3 through 17 years)
• Improved weight status (ages 3 through 17 years)
• Improved cardiorespiratory and muscular fitness (ages 6 through 17 years)
• Improved cardiometabolic health (ages 6 through 17 years)
• Improved cognition (ages 6 to 13 years)
• Reduced risk of depression (ages 6 to 13 years)

Adults and Older Adults

• Lower risk of all-cause mortality
• Lower risk of cardiovascular disease mortality
• Lower risk of cardiovascular disease (including heart disease and stroke)
• Lower risk of hypertension
• Lower risk of type 2 diabetes
• Lower risk of adverse blood lipid profile
• Lower risk of cancers of the bladder, breast, colon, endometrium, esophagus, kidney, lung, and stomach
• Improved cognition
• Reduced risk of dementia (including Alzheimer’s disease)
• Improved quality of life
• Reduced anxiety
• Reduced risk of depression
• Improved sleep
• Slowed or reduced weight gain
• Weight loss, particularly when combined with reduced calorie intake
• Prevention of weight regain following initial weight loss
• Improved bone health
• Improved physical function
• Lower risk of falls (older adults)
• Lower risk of fall-related injuries (older adults)

Note: The Advisory Committee rated the evidence of health benefits of physical activity as strong, moderate, limited, or grade not assignable. Only outcomes with strong or moderate evidence of effect are included in this table.

Box 2. What is a hazard ratio?

A hazard ratio is defined in the PAGA as follows (¹): “A measure of how often a particular event happens in one group compared to how often it happens in another group, over time. A hazard ratio of 1.0 means that there is no difference in survival or time to event between the two groups. A hazard ratio of greater than 1.0 or less than 1.0 means that survival or time to event was better in one of the groups. For example, a hazard ratio of 0.5 for mortality in people who participate in physical activity, compared with people who are inactive, indicates that active persons are 0.5 times (50%) less likely to have died at any particular point in time, compared with those who are inactive.” As shown in Figure 2, the hazard ratio shows greatest improvement (decreasing values) when shifting from sedentary to some activity, with continued improvement as activity levels increase.

Box 3. How are MET-hours per week determined?

MET stands for metabolic equivalent and reflects “the ratio of the work metabolic rate to the resting metabolic rate” or more simply stated “is roughly equivalent to the energy cost of sitting quietly” (⁷). To determine MET-hours per week, check out the MET value for the activity (see this web site for MET values for a wide variety of activities: https://sites.google.com/site/compendiumofphysicalactivities/home) and then multiply by the number of hours that the activity was done over the course of a week. For example, briskly walking at 3.5 mph on a firm level surface has a MET value of 4.3. If the weekly total for an exercise program at that pace was 180 minutes (3 hours), then the MET-hours per week would be 12.9. This amount of activity falls within the portion of Figure 2 with a lower hazard ratio.