and burns in a day, but the environments in which people live can have a profound impact on the amount of physical activity in which they engage. Public policy plays a role: declines in the rates at which children walk to school and adults use public transportation, for example, have coincided with the obesity epidemic, and such trends in part reflect changes in zoning and land use, funding for public transportation, and other policies. James Sallis, professor of psychology at San Diego State University, and Christine Hoehner, assistant professor in the Division of Public Health Sciences at Washington University in St. Louis, discussed the environmental and policy factors that likely affect physical activity levels, especially in young people; the pros and cons of existing ways of measuring the effects of the environment; and possible ways to improve measurement in this area.


Presenter: James F. Sallis

An ecological model of health behavior, Sallis explained, is a way of taking into account the impacts of society and culture, the physical environment, and public policy on the behavior of individuals, who are also influenced by biological and psychological factors and their own skills and knowledge. Figure 2-1 illustrates the complexity of the ways in which the environment affects levels of physical activity. The shaded circle represents the four domains in which people can be active: at home, at work or school, during recreation, and in moving from place to place. The other circles depict the many factors that influence how active people are in each domain. Thus, for example, the upper right quadrant shows how people’s level of activity while commuting, doing errands, and making other trips depends on their own characteristics; their perceptions of how convenient and accessible different modes of transport might be; the characteristics of the immediate environment (e.g., paths for biking and walking, traffic); and policies such as zoning codes, traffic management, and investments in public transportation.

Settings where it is possible to walk and bike to everyday destinations and to engage in outdoor recreation (such as in parks and playground) support physical activity. What these settings have in common, Sallis noted, is that none of them are under the control of the public health sector. He explained that policies, whether formal or informal, issued by government or the private sector, can affect physical activity in four ways. First, zoning and building codes and the design of transportation and recreation facilities all affect the built environment. Second, policies affect programs, such as physical education requirements in schools and sports programs and

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