There has been a good deal of attention given to the importance of physical activity in achieving good health in the media. This is largely due to the recent rise in overweight and obesity in population and the vast body of evidence on the benefits of physical activity in weight management and other health effects. Physical activity confers numerous benefits to health through a number of physiological mechanisms. Commissioned as a response to the rising levels of obesity in the U.S., in 1996 the U.S. Department of Health and Human Services Surgeon General’s report on physical activity and obesity was the first to bring to the forefront the health consequences of physical activity (U.S. Department of Health and Human Services, 1996). Based on this and a number of other comprehensive reviews of the literature, physical activity affects a variety of health outcomes:
- All cause mortality
- Cardiovascular disease
- Diabetes mellitus
- Cancer (colon and breast)
- Bone and joint diseases (osteoporosis and osteoarthritis)
- Mental health
Reviews of physical activity interventions suggest that people may be more willing and able to adopt moderate physical activities, once such activities are set in motion they are more inclined to maintain them over time, as compared with other types of vigorous physical activity (Frank and Engelke, 2001). Physical activities that are incorporated into daily life or have an inherent meaning, or lifestyle activities, rather than structured exercise regimens, are good strategy for increasing physical activity (Frank et al, 2003). Even relatively small changes in physical activity can translate into potentially large changes in weight trends at the population level (Morabia & Costanza, 2004). It is estimated that 60 minutes of slow walking and 30 minutes of moderate or brisk walking expends 100 calories for average adults (Morabia & Costanza, 2004). The general consensus is that a total of 30 minutes of moderate to vigorous physical activity, which can be achieved via brisk walking or cycling, on most days of the week, reduces the risk of cardiovascular diseases, diabetes and hypertension, and helps to control blood lipids and body weight (Pate, Pratt, Blair, et al, 1995). These benefits are conferred even if the activities are done in short ten- to fifteen-minute episodes. Thus, physical activity recommendations for adults call for at least 30 minutes of moderate to vigorous activity per day for health benefits. While the benefits of physical activity increase with the intensity and frequency of physical activity, the greatest come when people who have been sedentary engage in some form of physical activity.
According to the Centers for Disease Control, levels of physical activity can be determined in a number of ways. These include:
- Talk Test- One who is engaged in light activity should be able to sing at this intensity; at moderate activity levels, one should be able to carry on a conversation comfortably; if the person becomes winded or no longer able to carry on the conversation comfortably, the activity can be considered vigorous.
- Target Heart Rate and Estimated Maximum Heart Rate- These two values provide a target zone for a person’s heart rate during physical activity and are based on age (220- age). For example, a person’s target heart rate at moderate activity levels should be 50%-70% of his or her maximum heart rate. During vigorous activity levels a person’s target heart rate should be 70% – 85%.
- Perceived Exertion- The Borg Rating of Perceived Exertion is a subjective measure that helps to evaluate how hard an individual feels like his/her body is working. It can provide fairly good estimates of actual heart rates during physical activity.
- Metabolic Equivalent (MET) Level- A unit used to estimate the amount of oxygen used by the body during physical activity.
Downstream Health Effects
Inadequate levels of physical activity have been linked with a number of health outcomes that extend beyond obesity and overweight. These include: hypertension, cancer, diabetes, cardiovascular disease, impaired mental health, and bone and joint disease. As such, physical activity is a critical determinant of health that has the potential to positively or negatively influence a host of health outcomes.
Policies and Other Determinants
Policies can affect physical activity through changes in the built environment, including modifications in transportation, land use, and workplace environment, or through economic incentives for engaging in activity. Physical activity is associated with numerous physiologic and mental health benefits in both the short- and long-term.
- Walkable communities, not parks or fitness facilities, are where most people get most of their daily physical activity. Elements conducive to walkability include: wide, well-maintained sidewalks, signalized street crossings, slower traffic and narrower streets at crossings, street trees, destinations (shops, restaurants, etc.), and security. For more information see Active Living by Design and Project for Public Spaces
- Sprawl is associated with poorer mental health (Sturm and Cohen, 2004). Sprawl has a negative effect on physical activity as it increases travel time and forces people to travel out of their neighborhood for many everyday tasks, such as shopping, eating, working and going to school. To be effective, efforts to control sprawl need to be combined with efforts to promote mixed use development and mass transit
- School policies (and the adherence to such policies) have the ability to increase physical activity in general, and specifically moderate to vigorous activity levels among students. An increase in trained physical activity professionals, smaller class sizes and the elimination of physical education exemptions are just a few examples of how physical activity levels can be positively influenced