Mediators of physical activity maintenance during a 12-month randomized controlled trial among breast Cancer survivors.

Purpose: To explore the theoretical constructs that functioned as mediators of interventions for moderate-to-vigorous physical activity (MVPA) maintenance among breast cancer survivors.

Method: 161 survivors were randomized into 3 groups: Reach Plus, Reach Plus Message or Reach Plus Phone. All participants received a 3-month theory-based intervention delivered by volunteer coaches. During months 4-9, all participants monitored their MVPA and received feedback reports. Additionally, Reach Plus Message received weekly text/email messages and Reach Plus Phone received monthly calls from their coaches. Assessments of weekly MVPA minutes and theoretical constructs (self-efficacy, social support, physical activity [PA] enjoyment and PA barriers) were obtained at baseline, 3, 6, 9 and 12-months.

Analyses: Using a multiple mediator analysis with a product of coefficients approach, we examined mechanisms associated with between-group differences over time in weekly MVPA minutes.

Results: Self-efficacy mediated effects of Reach Plus Message vs. Reach Plus at 6 (ab = 16.99) and 9 M (ab = 27.45); social support mediated effects at 6 (ab = 4.86), 9 (ab = 14.30) and 12 M (ab = 6.18). Self-efficacy mediated effects of Reach Plus Phone vs. Reach Plus at 6 (ab = 18.76), 9 (ab = 28.93) and 12 M (ab = 18.18). Social support mediated effects of Reach Plus Phone vs. Reach Plus Message at 6 (ab=-5.50) and 9 M (ab=-13.20); PA enjoyment mediated effects at 12 M (ab=-3.63).

Conclusions: PA maintenance efforts should focus on strengthening breast cancer survivors' self-efficacy and obtaining social support.The trial was registered at ClinicalTrials.Gov: NCT02694640 (Feb. 26, 2016).