Abstract
BACKGROUND: Researchers theorize that interventions increase physical activity by influencing key theory-based mediators (e.g., behavioral processes). However, few studies have been adequately powered to examine the importance of mediators. PURPOSE: This study examined both physical activity behavior and psychosocial mediators in a randomized trial specifically powered to detect mediation. METHODS: Healthy, sedentary adults (n = 448; 70 % Caucasian, 87 % women, mean age was 43) were randomly assigned to either a 6-month print-based theory tailored physical activity intervention (n = 224) or a 6-month health/wellness contact control arm (n = 224). RESULTS: The print intervention arm exhibited greater increases in physical activity than the control arm at 6 and 12 months (p < .05). Additionally, behavioral processes were found to be an important mediator of physical activity behavior. CONCLUSIONS: It is important for researchers and practitioners to focus on increasing behavioral strategies for physical activity adoption. Future studies should examine other potential mediators of physical activity.