Mediators of a 12-month change in physical activity in ethnically diverse sample of postpartum women.

Purpose: Understanding theoretically derived social and behavioral mediators of long-term increases in physical activity (PA) in a vulnerable population at risk for being underactive is needed to inform future research, clinical applications, and public health efforts. This is an analysis of potential mediators of an intervention that increased long-term (12-month) moderate-to-vigorous physical activity (MVPA) in postpartum (2-12months) women in a randomized trial, using a longitudinal analysis.

Methods: Healthy, underactive (i.e., not meeting national guidelines for MVPA) women (n = 311; mean age = 32 ± 5.6 years, 85% minorities) with infants (mean age: 5.7 ± 2.8 months) were randomly assigned to either a tailored eHealth condition consisting of personalized telephone counseling plus access to a website tailored to new mothers' MVPA issues or to a standard MVPA materials-only website. MVPA was assessed via surveys completed at baseline, then 6 and 12 months later. Theoretically derived mediators included social support for MVPA, self-efficacy to increase MVPA, barriers to increasing MVPA, and benefits of increasing MVPA.

Results: All mediators, except benefits, improved over the 12 months in the tailored eHealth condition. The tailored condition's effect on increasing MVPA from 6 months to 12 months was mediated by an increase in social support from baseline to six months. No other hypothesized mediators were significant.

Conclusion: Our results demonstrated that learning strategies to increase social support for MVPA was instrumental in new mothers' increase in MVPA over a 12 month intervention. During this brief but impactful life-stage, where the focus can understandably be on her baby, being able to elicit support from friends and family may facilitate women's efforts to focus on their own needs with respect to MVPA.

Trial Registration: ClinicalTrials.gov number.