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 stre