National Association for Sport and Physical Education, American College of Sports Medicine) are known to influence youth’s school-related physical activity. Understood as well is that the strength of that influence is, in turn, affected by incentives and enforcements associated with those guidelines, recommendations, and policies (see Figure 1-3 in Chapter 1). What remains unclear is which guidelines, recommendations, policies, incentives, and enforcements are most influential in today’s social milieu.
What should also be apparent is that, despite some excellent research and a few good public health surveillance systems, current monitoring of overall and school-related physical activity behaviors and school-related policies and practices that enable or impede those behaviors is inadequate. These deficiencies have arisen for several reasons. First, physical activity has only recently been acknowledged as a vital public health issue, so monitoring of the volume of physical activity at the population level is a recent objective with still insufficient priority. The Physical Activity and Health Branch of the Centers for Disease Control and Prevention (CDC) was not established until 1996, and the first formal federal-level physical activity guidelines were not published until 2008 (HHS, 2008). Second, physical activity is a notoriously difficult behavior to measure. Third, understanding of the types and amounts of physical activity relevant to health and health outcomes is still growing. The types and amounts of physical activity recommended for children and adolescents have changed several times in the past 20 years, frustrating efforts to monitor trends. Fourth, information is scarce on prevalence and trends for policies that may enable (or inhibit) physical activity. Examples include school- and district-level policies on recess and training for physical education teachers, as well as community or neighborhood policies on active transport to and from school. Monitoring of policies and practices is improving but needs expansion and maturation. Finally, schools and school districts vary greatly in size, resources, environmental setting, urbanization, population characteristics, traditions, and policies. Summary assessments and measures may capture the national gestalt but omit important differences among subgroups.
Physical Activity Versus Exercise
Physical activity is defined as all human movement; it is done at some rate of energy expenditure in all settings and for many different purposes. Exercise is a subcomponent of physical activity that is done for the purpose of increasing physical fitness. Intensity (i.e., rate of energy expenditure) is an important descriptor of physical activity because different intensities have different physiologic effects. Both physical activity and exercise encompass the full range of energy expenditure.