Mediators of a randomized controlled physical activity intervention for breast cancer survivors

Physical activity (PA) interventions diminish some of the physical and psychosocial sequelae of breast cancer diagnosis and treatment. To increase intervention efficacy and portability, it is necessary to determine the factors mediating intervention effects on physical and psychosocial outcomes. This study presents mediator analyses from a randomized controlled trial of a home-based PA intervention (focused primarily on brisk walking) for breast cancer survivors. Eighty-six survivors were randomized to PA or contact control groups (mean age = 53.42 years, SD = 9.08 and 52.86 years, SD = 10.38 respectively; mean time since diagnosis < 2 years). The PA intervention was based on the transtheoretical model (TTM). Kraemer's approach was used to test hypothesized mediators. TTM variables did not mediate intervention effects on PA. Data indicate that increases in moderate-intensity PA and improved fitness may mediate intervention effects on vigor (beta=.21; beta=.01) and fatigue (beta=.24; beta=.05) and suggest the value of future research on these potential mediators.