Examining Psychosocial Mediators of Exercise Behavior

BACKGROUND:

Physical inactivity is related to many health problems, including increased risk of
cardiovascular disease, hypertension, and cancer. Despite the health consequences of a
sedentary lifestyle, only 25 percent of Americans meet the recommended levels of physical
activity. Researchers postulate that theory-based interventions effectively influence
physical activity behavior by changing theoretical constructs believed to be important for
behavior change (i.e., potential mediators), such as self-efficacy (i.e., confidence in
one's ability to be physically active). Unfortunately, previous studies have generally
failed to adequately test the mediating effect of theoretical constructs using appropriate
statistical mediator analyses as recommended by leading behavioral scientists and
statisticians.

DESIGN NARRATIVE:

The study will examine the mediating effect of theoretical constructs based on the
Transtheoretical Model (TTM) and Social Cognitive Theory (SCT). The study will address the
methodological, measurement, and statistical limitations of previous studies. The
investigators will randomly assign 420 healthy sedentary individuals to either a
theory-based physical activity intervention or a contact control group. Physical activity
behavior and the potential mediators will be assessed monthly over 12 months. They
hypothesize that constructs based on the TTM and SCT (i.e., behavioral processes, cognitive
processes, self-efficacy, and decisional balance) will mediate the relationship between
group assignment (intervention vs. contact control) and physical activity behavior, such
that the effect of the intervention on physical activity behavior relative to the contact
control group will be attenuated when controlling for the mediators. They will also examine
the importance of particular mediators for different population groups (e.g., age, gender),
which will help to create more effective interventions for these groups. Finally, they will
conduct a cost analysis to not only inform policy makers of the cost of delivering the
intervention within our study but also to estimate the cost of delivering each component of
the intervention (i.e., mediator). The analysis will estimate the cost of future refined
interventions that incorporate those active components that affect the mediators and
physical activity in this study. In summary, the study will identify which mediators (i.e.,
theoretical constructs) are most effective for increasing physical activity, which will have
an important public health impact given that this will likely lead to more efficacious and
less costly interventions.

Inclusion Criteria:

- In good health

- Living a sedentary lifestyle