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Exercise science, public health, and medical experts recommend that everyone engage in regular physical activity throughout their lifespans (86–88). Engaging in regular physical activity is a behavior that serves as a modifiable risk factor for preventing premature mortality as well as preventing or managing chronic diseases. Considering that physical inactivity is the fourth leading cause of death worldwide (99), that half of the adults in the United States have a chronic disease such as heart disease, cancer, or diabetes (94), and that these diseases contribute to disability and premature death (56,101), it is imperative that physical activity, along with eating a healthy diet (85) and avoiding tobacco use (90), be promoted as part of a healthy lifestyle so that people can decrease their risk of chronic disease and/or manage their conditions. The purposes of this chapter are to describe physical activity and the recommended amounts as well as provide several examples of the benefits of physical activity.
The terms physical activity, exercise, and physical fitness are often used in research studies and are worthy of clearly defining. Physical activity is defined as “any bodily movement produced by skeletal muscles that results in energy expenditure. The energy expenditure can be measured in kilocalories” (19). The total amount of caloric expenditure associated with physical activity is determined by the amount of muscle mass producing bodily movements and the intensity, duration, and frequency of muscular contractions (83). Examples of physical activity include walking, gardening, or riding a bicycle.
Physical activity should not be confused with exercise, which is a subset of physical activity performed for the purpose of improving or maintaining physical fitness (19). Physical fitness is an attained set of attributes (e.g., muscular strength, muscular endurance, cardiorespiratory endurance, flexibility, and body composition) that relates to the ability to perform physical activity (3). Typically, exercise is planned, structured, and repetitive as in jogging or swimming. Although physical activity and physical fitness both show a strong dose-response relationship with healthy outcomes, the relationship is more pronounced for physical fitness and healthy outcomes (3,13,96). In fact, the terms physical activity and exercise are sometimes used interchangeably. As some experts noted, “The intent is to recognize that many types of physical movement may have a positive effect on physical fitness, morbidity, and mortality” (22).
Given that the majority of Americans and many others throughout the world are not engaging in adequate health-maintaining and disease-preventing physical activity, promoting physical activity may be more conducive to engaging sedentary populations prior to recommending exercise or physical fitness. Although exercise or physical fitness may have more health benefits, engaging in physical activity as opposed to exercise may be a healthy first step for most physically inactive people.
Physical activity and exercise are behaviors, whereas physical fitness is an outcome of behaviors. It can often be confusing to determine which term to use. Each term represents a variable that can be measured. For example, cardiorespiratory endurance (a component of physical fitness and an outcome of exercise behavior) can be measured by conducting the exercise and testing protocol as outlined in the ACSM’s Guidelines for Exercise Testing and Prescription, 9th edition (67). Although cardiorespiratory fitness testing is reliable and valid and can be conducted accurately by exercise professionals, it can also be time-consuming and labor-intensive. Physical activity can be assessed through large-scale surveys or by using objective monitoring devices (e.g., pedometers, accelerometers); however, the accuracy or precision of the physical activity assessment may not compare favorably with the accuracy or precision of physical fitness. For large-scale, population-based studies, such as epidemiological or public health studies, physical activity may be the most feasible, cost-effective, and practical behavior to measure. For purposes of this chapter, literature review searches using the terms physical activity, exercise, and physical fitness were used when determining relationships to chronic diseases.
There has been substantial research regarding decreasing sedentary behavior in addition to engaging in adequate physical activity (11). Sedentary behavior can be defined as sitting or reclined while engaging in minimal energy expenditure (≤1.5 metabolic equivalents [METs]) (75,81). Physical inactivity can be defined as not meeting the recommended 30 minutes of moderate-intensity physical activity on at least 5 days every week, 20 minutes of vigorous-intensity physical activity on at least 3 days every week, or an equivalent combination achieving 600 MET-minutes per week (30). One MET represents 3.5 mL ∙ kg−1 ∙ min−1 of oxygen consumption and is a method for estimating energy expenditure during physical activity (1,2). Light-intensity physical activity (e.g., walking) can be defined as requiring <3.0 METs, moderate-intensity physical activity (e.g., jogging) as 3.0–5.9 METs, and vigorous-intensity physical activity (e.g., running) as ≥6 METs (31,78). A variety of physical activity and their ancillary METs can be found at sites.google.com/site/compendiumofphysicalactivities/. It is recommended that individuals who are less fit begin with lesser intense physical activity prior to engaging in more intense activity (31). Regarding obesity and weight loss, further guidelines recommend from 45 to 90 minutes of moderate- to vigorous-intensity physical activity (74,84).
Physical activity is a behavior that represents the interaction of the person and his or her social and physical environments and can be categorized in numerous ways (19,71). Typically, four physical activity domains include recreation, transport, occupation, and household. Active living incorporates exercise, recreational activities, household and occupational activities, and active transportation (72). Likewise, physical inactivity, or the lack of meeting the recommended amount of physical activity, may include categorizations such as sedentary behavior, walking, and sitting (see Chapter 2 for a more detailed discussion of physical inactivity and sedentary behavior).
Addressing physical activity behavior in an ecological model framework helps exercise scientists, public health, and medical experts plan, develop, implement, and evaluate physical activity interventions and policies (71,73,78). Physical activity behavior is influenced by intrapersonal (biological, psychological), interpersonal/cultural, organizational, physical environment (built, natural), and policy (laws, rules, regulations, codes) (54). Physical activity interventions and policies are most effective when they operate on multiple levels (40).
The current guidelines for physical activity are published in the 2008 Physical Activity Guidelines for Americans, also known as the current federal physical activity guidelines (86). The guidelines are the following:
All adults should avoid inactivity. Some physical activity is better than none, and adults who participate in any amount of physical activity gain some health benefits.
For substantial health benefits, adults should do at least 150 minutes (2 hours and 30 minutes) a week of moderate-intensity, or 75 minutes (1 hour and 15 minutes) a week of vigorous-intensity aerobic physical activity, or an equivalent combination of moderate- and vigorous-intensity aerobic activity. Aerobic activity should be performed in episodes of at least 10 minutes, and preferably, it should be spread throughout the week.
For additional and more extensive health benefits, adults should increase their aerobic physical activity to 300 minutes (5 hours) a week of moderate-intensity, or 150 minutes a week of vigorous-intensity aerobic physical activity, or an equivalent combination of moderate- and vigorous-intensity activity. Additional health benefits are gained by engaging in physical activity beyond this amount.
Adults should also do muscle-strengthening activities that are moderate or high intensity and involve all major muscle groups on 2 or more days a week, as these activities provide additional health benefits.
Furthermore, Healthy People 2020 (32), the nation’s health agenda, set a goal to improve health, fitness, and quality of life through daily physical activity and delineated 36 objectives related to the promotion of physical activity across the lifespan (Box 1.1).
Healthy People 2020 Physical Activity Objectives
HealthyPeople.gov. Physical Activity [Internet]. Washington (DC): Office of Disease Prevention and Health Promotion ; [cited 2017 Oct 2]. Available from: www.healthypeople.gov/2020/topics-objectives/topic/physical-activity/objectives
Healthy People 2020’s objectives were derived from seminal research and meta-analyses in exercise physiology, public health, and medicine to reach all Americans in achieving optimal quality and quantity of life. For example, Objective PA-2, “Increase the proportion of adults who meet current Federal physical activity guidelines for aerobic physical activity and for muscle-strengthening activity,” is derived from the Centers for Disease Control and Prevention (CDC) and American College of Sports Medicine’s (ACSM) issuance of a public health recommendation on the types and amounts of physical activity for health promotion and disease prevention across the lifespan. The special communication article, published in the Journal of the American Medical Association, concluded that “every US adult should accumulate 30 minutes or more of moderate-intensity physical activity on most, preferably all, days of the week” (66).
Later, the American Heart Association (AHA) and ACSM’s expert panel of scientists, physicians, epidemiologists, exercise scientists, and public health specialists convened to update and clarify the recommendations. These updates published in Medicine & Science in Sports & Exercise® (31), as well as in Circulation (2007), included the following:
To promote and maintain health, all healthy adults aged 18 to 65 yr need moderate-intensity aerobic (endurance) physical activity for a minimum of 30 min on five days each week or vigorous-intensity aerobic physical activity for a minimum of 20 min on three days each week.
I (A). Combinations of moderate- and vigorous-intensity activity can be performed to meet this recommendation.
IIa (B). For example, a person can meet the recommendation by walking briskly for 30 min twice during the week and then jogging for 20 min on two other days. Moderate-intensity aerobic activity, which is generally equivalent to a brisk walk and noticeably accelerates the heart rate, can be accumulated toward the 30-min minimum by performing bouts each lasting 10 or more minutes.
I (B). Vigorous-intensity activity is exemplified by jogging, and causes rapid breathing and a substantial increase in heart rate. In addition, every adult should perform activities that maintain or increase muscular strength and endurance a minimum of two days each week.
IIa (A). Because of the dose-response relation between physical activity and health, persons who wish to further improve their personal fitness, reduce their risk for chronic diseases and disabilities or prevent unhealthy weight gain may benefit by exceeding the minimum recommended amounts of physical activity.
The aforementioned physical activity recommendations describe minimal frequency, intensity, and time amounts in order to achieve or maintain health. The recommendations also suggest that accumulating more than the recommended amounts is better. Furthermore, other health behaviors, such as healthy eating, may be considered when trying to achieve energy balance or weight loss (31,35).
Considering that 1 in 4 adults (20% of men and 27% of women) worldwide are insufficiently physically active, physical inactivity has been listed as a global pandemic (42,100). In the United States, approximately one-half of the proportion of adults and about one quarter of high school students meet the guidelines for aerobic physical activity (12,37,38). Typically, reports refer to the aerobic recommendations, although there are muscle-strengthening and flexibility recommendations as well. The latest self-report data indicate that 47% of adults in the United States meet neither the aerobic nor muscle-strengthening guideline, 3% meet the muscle-strengthening guideline only, 29% meet the aerobic guideline only, and 21% meet the full guidelines for both aerobic and muscle-strengthening activity based on their participation in leisure-time physical activity (12).
The prevalence of those meeting physical activity recommendations is not equitable among demographic sectors. Health equity is achieved when every individual has the opportunity to “attain his or her full health potential,” and no one is “disadvantaged from achieving this potential because of social position or other socially determined circumstances” (20). Differences in sex, race/ethnicity, age, educational attainment, family income, family type, country of birth, disability status, geographic location, health insurance status, sexual orientation, and marital status in national physical activity data reveal that disparities exist.
An example of a health disparity is the difference in physical activity behaviors between men and women. In 2008, self-report survey results indicated that 47.4% of men met the recommendation, and the number steadily increased to 54.1% in 2013. For women, the gains were not as noteworthy. In 2008, 43.6% of women met the physical activity recommendation, and the proportion increased to 46.1% in 2013. Furthermore, men were more likely than women to have met the aerobic and muscle-strengthening physical activity recommendations (12).
Recent data indicate that non-Hispanic White adults (23%) are more likely to meet the full guidelines for both aerobic and muscle-strengthening activity based on their participation in leisure-time physical activity than Hispanic adults (16%) or non-Hispanic African American adults (17%) (12). Also, younger adults are more active than older adults, and as age increases, physical activity decreases.
Social and environmental circumstances, or social determinants of health, can have an impact on a person’s ability to be physically active. For example, not having access to safe recreational facilities or sidewalks for families to walk to school or work may negatively affect engagement in physical activity. Research results indicate that as poverty levels decrease, the percentage of adults who are physically active increases (12). See Box 1.2 for other examples of disparities in physical activity among certain demographic characteristics.
Prevalence of Disparities for Meeting Physical Activity Recommendations
More men (54.1%) met the recommendations than women (46.1%).
More Native Hawaiian or other Pacific Islander (64.5%) met the recommendation than White, non-Hispanic (53.4%), two or more races (50.7%), Asian (49.8%), American Indian or Alaska Native (46.6%), Hispanic or Latino (42.7%), and non-Hispanic African American adults (41.3%).
More younger adults, aged 18–24 years (61.5%), met the recommendations than adults aged 25–44 years (55.1%), 45–54 years (48.4%), 55–64 years (44.1%), 65–74 years (41.8%), 75–84 years (31.2%), and 85 years and older (18.3%).
For adults aged 25 years and older, those with higher educational attainment reported a higher rate of meeting the recommendation than those with lower educational attainment (e.g., advanced degree, 64.7%; 4-yr college degree, 59.4%; associate degree, 50.3%; some college education, 49.1%; high school graduate, 39.7%; and less than high school education, 30.5%).
Those who lived in a family with a higher income met the recommendations more than those who live with families with lower income (e.g., >600% over the poverty threshold, 65.8%; 400%–599%, 57.2%; 200%–399%; 48.3%; 100%–199%, 38.6%; and <100%, 35.6%).
Adults who had a spouse or partner were more active (55.3%) than single (52.6%), two-parent family with child or children (52.8%), single parent with child or children (41.5%), or other (43.0%).
Adults who were born in the United States (51.6%) met the recommendations more than adults who were not born in the United States (43.6%).
Those individuals without activity limitations (53.9%) met the guidelines for physical activity more than individuals with activity limitations (30.5%).