Analyzing Theoretical Mechanisms of Physical Activity Behavior Change in Breast Cancer Survivors: Results from the Activity Promotion (ACTION) Trial

Abstract

We previously reported that a physical activity (PA) behavior change intervention based on the theory of planned behavior (TPB) increased PA and quality of life in breast cancer survivors. To examine the effects of our interventions on TPB variables and to determine if PA at 12 weeks follow-up was mediated by TPB variables at 4 weeks. Breast cancer survivors (N = 377) were randomly assigned to receive either a standard public health recommendation for PA (SR group), a step pedometer alone, or one of two TPB-based behavior change interventions consisting of print materials (alone or combined with a step pedometer). For the purpose of this study, we compared the two TPB-based intervention groups (INT group) to the SR group. Compared to the SR group, the INT group reported more favorable changes in instrumental attitude (mean difference = 0.13; 95% CI = -0.01 to 0.23; d = 0.19; p = 0.077), intention (mean difference = 0.33; 95% CI = 0.10 to 0.56; d = 0.33; p = 0.006), and planning (mean difference = 0.39; 95% CI = 0.04 to 0.73; d = 0.26; p = 0.027). Mediation analyses indicated that both planning and intention partially mediated the effects of the intervention on PA at 12 weeks. Our TPB-based behavior change intervention resulted in small improvements in the TPB constructs that partially mediated the effects of our intervention on PA behavior. Additional research with the TPB is warranted.