Background:
Although physical activity is associated with reduced risks of chronic disease, only about a third of U.S adults achieve recommended levels of physical activity. Policy strategies aimed at modifying aspects of the social, physical, economic, and information environments have been proposed as a potential solution to the growing problem of physical inactivity. Whereas individual- and community -level interventions affect only those people involved in the program itself, policy approaches can have an impact on a larger population, can better influence people who are difficult to reach, and are more cost-effective. In fact, the Task Force on Community Preventive Services recently recommended the use of policies to create places for physical activity and improved access to these places. Various policy approaches have been proposed to increase physical activity such as zoning regulations, building codes, and modifications to transportation infrastructure. In order to develop effective physical activity policies in these and other areas, greater understanding of the intervening variables linking public policy strategies to physical activity is needed. Theories of health behavior change offer a variety of psychosocial factors that are thought to predict health-related actions. Yet, there has been little attempt to describe the influence of physical activity policies on these mediating mechanisms.

Objectives:
The goal of the current paper is propose a conceptual model that describes linkages between policy strategies and intervening theoretical variables that may lead to physical activity change.

Methods:
The current paper describes how physical activity policies fall into in four strategies based on the primary approach taken to influence behavior: 1) providing information (e.g., point-of-decision prompts), 2) increasing or decreasing opportunities (e.g., building community trails), 3) requiring or prohibiting the behavior (e.g., pedestrian-only streets), and 4) providing incentives and disincentives (e.g., insurance credits). It then discusses each policy strategy in terms of the intervening theoretical variables involved in the causal pathway leading from that policy to behavior change. Six relevant health behavior theories are considered: Self-Determination Theory (SDT), the Transtheoretical Model (TTM), the Health Belief Model (HBM), the Theory of Reasoned Action (TRA)/Theory of Planned Behavior (TPB), and Social Cognitive Theory (SCT). Relevant research studies are reviewed to support the proposed conceptual linkages. The paper concludes by describing how this framework can be used to make predictions about the potential effectiveness of each policy strategy.

Results:
Table 1 describes potential relationships between policy strategies and theoretical mediators of physical activity change. Policies that provide information could influence physical activity by impacting perceived susceptibility (HBM), perceived severity (HBM), perceived benefits (HBM), outcome expectancies (TRA), attitudes toward the behavior (TPB), integrated motivation (SDT), and by moving individuals from precontemplation to contemplation (TTM). Policies that increase or decrease opportunities can impact physical activity by changing perceptions of barriers (HBM), action cues (HBM), self-efficacy (SCT), social norms and perceived behavioral control (TRA/TPB), intrinsic motivation (SDT), and by moving individuals from preparation into action (TTM). Policies that require or prohibit certain actions might affect behavior by providing cues to action (HBM), improving behavioral skills (SCT), increasing self-efficacy (SCT), changing social norms (TPB), and triggering external or introjected motivation (SDT). Lastly, policies that offer incentives or disincentives may influence physical activity by providing cues to action (HBM), changing attitudes towards the behavior and expected outcomes (TRA/TPB), utilizing external motivation (SDT), and by moving individuals move from preparation into action stages of change (TTM).

Conclusions:
The extent to which physical activity policy strategies impact theoretical mediators of health behavior change may provide an important indicator their potential effectiveness. Policies that successfully influence psychosocial factors know to predict physical activity may have the greatest impact on behavior.

Support:
This paper was written while the first author was at the University of Southern California.