UC San Diego

PURPOSE: Cancer survivors are highly sedentary and have low physical activity. How physical activity interventions impact sedentary behavior remains unclear. This secondary analysis examined changes in sedentary behavior among breast cancer survivors participating in a physical activity intervention that significantly increased moderate-to-vigorous physical activity (MVPA). METHODS: Insufficiently active breast cancer survivors were randomized to a 12-week physical activity intervention (exercise arm) or control arm. The intervention focused solely on increasing MVPA with no content targeting sedentary behavior. Total sedentary behavior, light physical activity (LPA), and MVPA were measured at baseline and 12 weeks (ActiGraph GT3X+ accelerometer). Separate linear mixed-effects models tested intervention effects on sedentary behavior, intervention effects on LPA, the relationship between change in MVPA and change in sedentary behavior, and potential moderators of intervention effects on sedentary behavior. RESULTS: The exercise arm had significantly greater reductions in sedentary behavior than the control arm (mean - 24.9 min/day (SD = 5.9) vs. - 4.8 min/day (SD = 5.9), b = - 20.1 (SE = 8.4), p = 0.02). Larger increases in MVPA were associated with larger decreases in sedentary behavior (b = - 1.9 (SE = 0.21), p < 0.001). Women farther out from surgery had significantly greater reductions in sedentary behavior than women closer to surgery (b = - 0.91 (SE = 0.5), p = 0.07). There was no significant group difference in change in LPA from baseline to 12 weeks (b = 5.64 (SE = 7.69), p = 0.48). CONCLUSIONS: Breast cancer survivors in a physical activity intervention reduced total sedentary time in addition to increasing MVPA. IMPLICATIONS FOR CANCER SURVIVORS: Both increasing physical activity and reducing sedentary behavior are needed to promote optimal health in cancer survivors. These results show that MVPA and sedentary behavior could be successfully targeted together, particularly among longer-term cancer survivors. CLINICAL TRIAL REGISTRATION: This study is registered at www.ClinicalTrials.gov (NCT02332876).